ith advancing technology, diagnostic im- aging techniques available for avian pa- tients now include ultrasound, fluoros- copy, computed tomography (CT) and nu- clear scintigraphy; however, routine radiography re- mains the most frequently performed imaging mo- dality in birds and frequently is diagnostic without the need for more sophisticated procedures. Informa- tion obtained from radiographs will frequently com- plement results from other testing methods, provid- ing for a more thorough evaluation of a disease process. Both risk and benefit to the patient should be consid- ered when radiography is used as a screening proce- dure in an apparently normal companion bird. In general, radiography should be performed only when indicated by historical information, physical exami- nation findings and laboratory data. Indiscriminate radiographic studies create an unnecessary risk to the patient and technical staff. Radiographic findings should always be correlated with surgical, endoscopic or necropsy findings. These comparisons will refine a clinician’s ability to detect subtle radiographic changes, and improve diagnostic capabilities and therapeutic results. W CHAPTER 12 IMAGING TECHNIQUES Marjorie C. McMillan
Transcript
ith advancing technology, diagnostic im-aging techniques available for avian pa-tients now include ultrasound, fluoros-copy, computed tomography (CT) and nu-
clear scintigraphy; however, routine radiography re-mains the most frequently performed imaging mo-dality in birds and frequently is diagnostic withoutthe need for more sophisticated procedures. Informa-tion obtained from radiographs will frequently com-plement results from other testing methods, provid-ing for a more thorough evaluation of a diseaseprocess.
Both risk and benefit to the patient should be consid-ered when radiography is used as a screening proce-dure in an apparently normal companion bird. Ingeneral, radiography should be performed only whenindicated by historical information, physical exami-nation findings and laboratory data. Indiscriminateradiographic studies create an unnecessary risk tothe patient and technical staff.
Radiographic findings should always be correlatedwith surgical, endoscopic or necropsy findings. Thesecomparisons will refine a clinician’s ability to detectsubtle radiographic changes, and improve diagnosticcapabilities and therapeutic results.
WC H A P T E R
12IMAGING
TECHNIQUES
Marjorie C. McMillan
Technical Considerations
The size (mainly thickness), composition (air, softtissue and bone) and ability to arrest motion are theprimary factors that influence radiographic tech-nique. Although the skeleton is easy to visualize,specific soft tissue structures within the coelomiccavity may be difficult to differentiate, especially insmaller birds. Interpretation of the radiographs maybe complicated by the blending of soft tissue struc-tures caused by the compact viscera, rudimentarymesenteric attachments and minimal fat. Even inobese birds, contrast of the coelomic cavity is mini-mally improved, suggesting that, radiographically,the opacity of avian fat is similar to that of soft tissue.In the absence of pathology, the air sacs providenegative contrast throughout the thorax and abdo-men that can help in differentiating structures.
Multiple factors influence the quality of a radio-graphic image. In radiographing the avian patient,the goal is to produce a properly positioned, detailedstudy with a long scale of contrast, minimal motionand the least exposure of the patient and technicalpersonnel to radiation. In general, the image qualityis controlled by:
the production of the image—influenced by radio-graphic equipment, technical settings (kVp, mAand time), focal-film distance, part-film distance,focal spot size and collimation;the recording of the image—influenced by the typeof film, cassette and screen combination; andthe development of the image—influenced by thedarkroom environment and type of processingequipment.
Attention to quality in all aspects of obtaining aradiograph will result in consistent, high qualityradiographs with reduced repeat rates, increased ef-ficiency, less patient stress, reduced radiation expo-sure and economic savings. A quality control programthat encompasses all the factors contributing to theradiographic image is beyond the scope of this chap-ter and appropriate references should be reviewed.3,5,25
Radiographic detail depends on sharpness of the im-age and radiographic contrast. Sharpness, the abilityto define an edge, is compromised by motion, unevenfilm-screen contact and a large focal spot. Radio-
graphic contrast is controlled by subject contrast,scatter, and film contrast and fog. Detail is improvedby using a small focal spot, the shortest possibleexposure time (usually 0.015 seconds), adequate fo-cus-film distance (40 inches), a collimated beam, sin-gle emulsion film and a rare earth, high-detailscreen. The contact between the radiographic cas-sette and the patient should be even, and the area ofinterest should be as close as possible to the film.
There is increasing discussion of the use of mammog-raphy machines for imaging avian patients. Whilethese machines do produce excellent quality imageswith extremely refined detail, the clinician should beaware that imaging requires exposure to high levelsof radiation in comparison to standard radiographs.In general, mammography machines can be consid-ered to deliver low-dose radiation therapy (levels ofradiation that cause tissue destruction), and thelong-term effect of exposing the body of a bird to thislevel of radiation is undetermined.
Radiographic Technique
The specific technical factors needed to obtain a highquality radiograph will vary with the type of radio-graphic equipment, film-screen combinations andvarious settings used for specific purposes. A tech-nique chart for the various species can be devel-oped.28 As a general rule, the clinician should choosethe lowest kV, a high mA and a short exposure time.7Usually, non-bucky techniques applicable for radio-graphy of cats provide reasonable radiographic set-tings for medium to large psittacine birds.5
In circumstances where single emulsion, rare earth,high-detail systems are used, kVp ranging from 60 to75 at five mAs (300mA, 1/60th of a second) usuallyprovides an appropriate scale of contrast and elimi-nates motion. In small Passeriformes, such as canar-ies and finches, reducing the focal-film distance byone-fourth (to 30 inches) and decreasing the mAs byone-half may improve the radiographic image. De-creasing the focal-film distance can result in loss ofdetail due to magnification; however, with small pa-tients, a shorter focal-film distance does not seem tocompromise the radiographic image.
Although the single-emulsion film and single screen,rare earth systems result in greater detail, they dorequire increased exposure when compared to doubleemulsion film-cassette combinations. Low-absorp-tion cassette fronts may provide comparable detailedstudies with less radiation exposure.29
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It is important to radiation safety tomaintain an adequate distance fromthe source of radiation by using tech-niques that do not require personnelto restrain the patient during a ra-diographic study. If hospital person-nel must be present during an expo-sure, they should wear a lead apron,lead gloves, thyroid shield, protectiveglasses and a film badge. No portionof a person’s body should be in theprimary beam, even if covered bylead. With practice, restrainingmethods can be developed so only thepatient is exposed to radiation.
Restraint and Positioning
Poor positioning is the most frequently encounteredfactor that compromises a radiographic study andhampers interpretation of subtle lesions. Some birdscan be adequately restrained for routine views withmechanical plexiglass devices and positioning aidssuch as sandbags, foam blocks, lead gloves, velcro,pipe cleaners and plastic and paper tape.10,18 Otherpatients will require isoflurane anesthesia to obtainthe most diagnostic radiographs; however, it shouldbe noted that anesthesia or chemical restraint forradiographic examination will decrease normal gas-trointestinal motility and as such is generally contra-indicated in studies to evaluate the function of thisorgan system. Anesthesia should be considered man-datory when radiographing strong, powerful birds orpatients that are fractious, highly stressed, experi-encing significant respiratory distress or those thathave an injury that may be exacerbated by strug-gling. If anesthesia is required, appropriate evalu-ation of the patient prior to anesthesia is indicated(see Chapter 39). With experience, a complete set ofdiagnostic, high quality radiographs can be obtainedin an anesthetized bird in less than five minutes.
If heavy metal intoxication is suspected in a criticallyill bird, a quick radiographic screening for metaldensities can be obtained by placing the bird in a bagand taking a DV radiograph. A horizontal beam ra-diograph can also be taken through the bag to pro-vide a lateral view. This technique is useful only todemonstrate radiographically detectable metal par-ticles (Harrison GJ, unpublished).
The most frequently performed radiographic studiesin companion birds are ventrodorsal (VD) and left-to-right lateral (LeRtL) whole body projections. To usea plexiglass restraint board, the neck of the bird justbelow the angle of the mandible is secured in thestock-like, contoured portion of a restrainer while thebody is still wrapped in a towel. For the VD view, thehead is restrained and the wings are extended 90degrees from the body and secured with sandbags,velcro straps or tape. The wings should be restrainedclose to the body to prevent iatrogenic fractures. Thelegs are pulled caudally and parallel to the body andsecured at the tarsometatarsus with tape or velcrostraps (Figure 12.0).
For the LeRtL view, the wing and leg restraints areloosened while the head and body are rotated intoright lateral recumbency. The dependent wing is ex-tended 90 degrees to the body and secured. A foamblock or other soft material is placed between thewings, and the left wing is extended and restrainedslightly caudally to the right. Placing a block of foambetween the wings helps to prevent overextensionand potential injury. Both legs are extended caudallywith slight tension and secured individually at thetarsometatarsus. The dependent leg is positionedslightly cranially. Securing the legs individuallyhelps to reduce rotation of the body, which is commonif the legs are fastened together. The beam should becollimated to the patient size to reduce scatter, andradiopaque right or left markers should be appropri-ately positioned.
In a symmetrically positioned VD view, the spine andsternum will be superimposed, and the scapulae,acetabula and femurs will be parallel (Figure 12.1).
FIG 12.0 A plexiglass restraint board can be used for positioning anesthetized or unanes-thetized birds for radiographs. An anesthetized bird is shown in the proper position for aVD radiograph.
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In LeRtL projection, the ribs, coracoid, acetabula andkidneys will be superimposed, if the positioning isaccurate (Figure 12.3).
While in the VD position, collimation may be used toobtain radiographs of the pelvis, craniocaudal projec-tion of the legs and mediolateral view of the wings(Figure 12.9, 12.10). The orthogonal view of the wingin the caudocranial projection requires horizontalbeam radiography. In the lateral position, views ofthe pelvis, spine and legs can be achieved (Figure12.11, 12.12).
Radiography of the skull requires general anesthesiato ensure accurate positioning and to minimize mo-tion. Complete evaluation of the skull requiresLeRtL, RtLeL, VD, dorsoventral (DV) and rostro-caudal (RCd, frontal sinus) views (Figure 12.5 to12.8). In evaluating skull trauma, left and right 75°ventrodorsal oblique views are recommended.7
Radiographic Interpretation
If radiographic films are manually processed, an in-itial assessment of positioning and technique can bemade during a “wet” reading; however, final interpre-tation should be reserved until the film is completelydry. The environment in which interpretation occursis important. A dimly lighted area with minimaldisturbance and an evenly illuminated viewing boxat eye level improves viewing conditions. Personalpreference determines whether an organ-by-organapproach or concentric circle system is used to evalu-ate the radiograph. Whichever method is chosen, it isimportant that the entire radiograph is studied, andthat the observer does not just focus on the lesion.Minifying and magnifying lenses may improve inter-pretation by enhancing detail or magnifying struc-tures, especially in smaller avian patients. It is ad-vantageous to use a standardized form whenrecording radiographic findings.
Neonatal Radiography
Stress should be minimized when radiographing neo-natal birds. The surface of the cassette should bewarmed with a towel to avoid placing a young bird ona cold surface. Paper tape should be used for re-straint to avoid damage to the numerous blood feath-
ers. In some circumstances, proper positioning maybe sacrificed in the best interest of the patient. Pres-sure must not be placed on a full crop to preventregurgitation and subsequent aspiration.
The abdomen of neonates appears pendulous be-cause the gastrointestinal tract is dilated, fluid-filledand blends with the other soft tissue organs (seeFigure 30.7). This results in a homogenous appear-ance to the coelomic cavity. The air sacs are relativelyindistinguishable. The skeleton is incompletely min-eralized and will have a reduced density, and frac-tures may be difficult to detect (Figure 12.76).
Musculoskeletal System
Radiographic AnatomyThe cranium of birds contains numerous connectionsto the sinuses, which are reflected radiographically.The osseous scleral ring is clearly visible radiog-raphically, while the interorbital septum that liesbetween the eyes is barely visible (Figures 12.5,12.6).
The articulation between the clavicle and sternum inbirds is membranous rather than bony. The distalends of the clavicle are fused, forming the furcula(wishbone) (Figures 12.1 to 12.4). The coracoid ar-ticulates with the cranial portion of the sternum andthe shoulder joint. Only the radial and ulnar carpalbones are present. The distal carpal bones are fusedwith each other and with the proximal ends of themetacarpal bones. This area is referred to as thecarpometacarpus. The digits are traditionally num-bered I (alular), II (major) and III (minor). Developedfeathers are hollow, and the rachis will have an airdensity center. Developing feathers contain blood tothe level of the pulp cavity and will appear as softtissue densities (Figure 12.9).
The spine is separated into cervical, thoracic, synsac-ral (fused thoracic, lumbar, sacral and caudal), free-caudal and fused caudal (pygostyle) sections. Thenumber of cervical vertebrae varies with the species(budgerigars = 11, Amazon parrots = 12). In Gallifor-mes, the last cervical vertebra is fused to the firstthree thoracic vertebrae. The number of thoracicvertebrae varies from three to ten depending on thespecies.
Ribs are present on the cervical and thoracic verte-brae. The cervical ribs have short, ventrally orientedspines that are fused to the cervical vertebrae. Thethoracic ribs are complete (number varies with thespecies) and are divided into two portions; the dorsal
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portion articulates with the vertebra and the ventralportion articulates with the sternum (Figure 12.1). Itshould be noted that not all ribs have a sternalportion. The sternal rib is equivalent to the mammal-ian costal cartilage. Uncinate processes that anchorthe caudal edge of several vertebral ribs to the cra-nial edge of the subsequent rib may be present onsome ribs (see Anatomy Overlay).
There are 10 to 23 synsacral vertebrae and 5 to 8 freecaudal vertebrae. The ilium and ischium are fusedand are also fused to the synsacrum. The pubic bonesare long, thin and unfused (except in ratites), pre-sumably as an adaptation for egg laying (Figure 12.1).
No separate tarsal bones occur. The proximal tarsalbones are fused with the tibia; this structure is termedthe tibiotarsus. The digital tarsal bones are fusedwith the metatarsal bones resulting in a tarsometa-tarsus. In parrots, each digit has one more phalangethan the number of the digit. For example, digit IIIis composed of four phalanges (Figures 12.11, 12.12).
Various portions of the skeletal system may be per-fused by air sacs in some avian species. The cervicalvertebrae may be perfused by the cervical air sac; thethoracic vertebrae, ribs and humerus may be per-fused by the interclavicular air sac; and the syn-sacrum and femur may be perfused by the abdominalair sacs (see Anatomy Overlay).
Avian long bones are characterized by thin cortices.The ossification of long bones is different in birdsthan in mammals, which should not be misinter-preted as pathology (see Chapter 42).
Radiographic Evidence of Skeletal DisordersCategorizing abnormalities aids in reducing the dif-ferential diagnoses and allows some judgement as tothe aggressiveness and chronicity of a lesion.15,24
The species and age of a bird influence the type ofmusculoskeletal pathology that will be encountered.In companion birds, bone changes associated withmetabolic bone disease and pathologic fractures aremore common than traumatic injury or infection.Congenital bone abnormalities are uncommon; how-ever, developmental changes associated with poorhusbandry and improper nutrition occur frequently.Hypovitaminosis D3 and calcium and phosphorus im-balances result in changes in the size, shape andlength of bones that are characterized by generalizedosteopenia and folding fractures secondary to osteo-malacia (see Figure 31.10).
Valgus deformity of the tibiotarsi (bow leg), kyphosis,scoliosis, lordosis and sternal compression may occursecondary to osteomalacia (see Figure 33.8). If thespinal or sternal abnormalities are severe, compro-mise of the thoracic cavity may occur that causesdisplacement of the heart and respiratory distress.“Splay leg” may be complicated by osteomalacia aswell as contracture of tendons and muscles, causingclenching of the feet and rotation at the stifle joint.Hypervitaminosis D3 can cause diffuse metastaticmineralization within soft tissues, particularly thekidneys (see Figure 21.3).7
Skeletal trauma may result in fractures, sprain inju-ries and concussions (see Chapter 16). Luxations areinfrequent and usually involve the digits, stifle orcoxofemoral joint, and often occur due to danglingfrom leg bands, inappropriate toys and unsafe enclo-sures (Figure 12.78). The important considerationsin the radiographic evaluation of fractures includelocation, articular involvement, bone density, peri-osteal reaction, soft tissue involvement and whetherthe fracture is simple or comminuted and open orclosed (see Chapter 42).
In companion birds, head trauma most often resultsin concussion and soft tissue injury. In birds, frac-tures of the cranium are infrequently discussed, pos-sibly because of the necessity of taking multiple ra-diographic views to delineate between normallysuperimposed structures of the head and fracturelines. Detection of non-displaced fractures generallyrequires a CT scan. Fractures of the jugal arch,pterygoid bone and displacement of the quadratebone have been reported (Figure 12.37).18 Penetrat-ing skull injuries occur in big bird-little bird encoun-ters and cat attacks.
Fractures of the cervical spine are infrequent, butmay be incorrectly diagnosed due to the normal sig-moid curve in this region. Accurate radiographs ofthe cervical spine require extension of the head and
CL INICAL APPL ICAT IONSA general approach to interpretation of skeletal disorders includesthe evaluation of:
Change in bone density (osteopenia or osteosclerosis)
Distribution of lesions (diffuse, monostotic or polyostotic)
Architecture of the bone (cortical changes, disruption in con-tinuity, size and shape, trabecular pattern)
Periosteal change (smooth or coarse, lamellar or irregular)
Margination (sharp, well-defined or poorly defined)
Soft tissue changes
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neck without rotation of the skull or body. Whenvertebral fractures occur, they are often located inthe caudal thoracic region or the synsacrum.7
Diaphyseal fractures of the extremities are the mostcommon traumatic injury. Acute fractures are char-acterized by sharp, well-defined margins, absence ofperiosteal response and concurrent soft tissue swel-ling (see Figure 16.16). Chronic fractures are charac-terized by rounding, flaring and indistinct fractureends, periosteal change and minimal soft tissue in-volvement or atrophy. Fracture repair depends onthe bone involved, location, type of fracture andchronicity. Avian fractures heal in a manner similarto that described for mammals, except the endostealcomponent is more pronounced.2 Healing is usuallycomplete within three to eight weeks. Lack of visuali-zation of the fracture lines and smooth, well-definedcallus bridging all cortices indicate complete healing(see Figure 42.2).
Osteolysis is the predominant radiographic changewith infectious or neoplastic processes, and differen-tiation between these etiologies will require biopsy(see Figure 25.8). Osteomyelitis and septic arthritismay occur secondary to open fractures, penetratingwounds, iatrogenic contamination, hematogenoussources, extension from air sac disease or pododer-matitis. Acute infection may show bone destructionwith minimal periosteal reaction. Periosteal changeis usually present with chronic infections (see Figure33.7).
Fungal osteomyelitis may cause pronounced pe-riosteal reaction or increased medullary opacity dueto granuloma formation. Mycobacterium spp. mayalso cause medullary granulomas as well as septicarthritis and bone lysis. Infection is most common inthe extremities, and vertebral osteomyelitis is rare.Osteomyelitis in the calvarium is usually due toextension from chronic rhinitis, sinusitis or periorbi-tal lesions, and aspergillosis and mycobacteriosismay be involved. When infection occurs in associa-tion with fractures, there is often delayed union, andchronicity is characterized by regions of sclerosis andlysis. Fragments of increased density suggest com-promised vascular supply and potential sequestraformation.
With acute septic arthritis, joint effusion due to syno-vitis may be the only radiographic change, and arth-rocentesis is necessary for diagnosis (Figure 12.77).Bacteria, mycoplasma, mycobacteria and parasitesmay be causative agents. As an infection progresses,
destruction of articular cartilage results in loss ofjoint space, and osteolysis and periosteal changesmay occur in the epiphysis and metaphysis. Distaljoints are most commonly affected, especially whenthe infection is secondary to septic pododermatitis.Occasionally, luxation of the affected joint may occur.Effusion and diminished joint space may occur alsowith degenerative joint disease, but they are usuallyaccompanied by chronic changes such as periarticu-lar lipping, sclerosis of subchondral bone and osteo-phytes (see Figure 42.11).
Primary bone neoplasia such as osteosarcoma is un-common but has been reported in the proximalhumerus, maxilla and wing tips. Bone neoplasia isfrequently characterized by osteolysis with minimalperiosteal change; however, osteoblastic tumors withmarked periosteal reaction do occur. Most tumorsinvolving bone occur secondary to soft tissue neo-plasia (see Figure 25.2). These tumors are frequentlyassociated with soft tissue swelling, bone destructionand pathologic fractures, and biopsies are necessaryto differentiate between tumors and osteomyelitis.Metastatic bone lesions are rare.
Normal pre-ovulatory hens will have an increasedmedullary bone density (polyostotic hyperostosis).Prolonged, abnormally elevated estrogen levelscause a diffuse, increased medullary bone density.14
The bones have a “marble” or mottled appearance,depending on whether bone deposition is uniform orpatchy (Figure 12.65). Discrete, nodular regions ofbone resembling osteomas occasionally occur on theribs, vertebrae or pubic bones. Polyostotic hyperos-tosis has also been reported in hens with oviductaltumors and in cocks with sertoli cell tumors.21,23
Hypertrophic osteopathy is rare, but has been re-ported in association with pericardial effusion.4 Ra-diographic lesions were characterized by extensive,fine, brush-like periosteal reaction involving most ofthe long bones. In other species, hypertrophic oste-opathy is associated with pulmonary disease andneoplasia involving the lungs, bladder or liver.
Cardiovascular System
Radiographic AnatomyIn general, the base of the heart is angled craniodor-sally and lies at the second rib. The apex is directedin a caudoventral direction and lies between the fifthand sixth ribs (varies with species) (Figure 12.1 to12.4, 12.15, 12.16). The size and shape of the cardiac
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silhouette will vary with the phase of respiration,cardiac cycle and species.
In mammals, various formulas for measuring thecardiac size from radiographs have proved inaccu-rate, and currently echocardiography is the mostreliable method for assessing cardiac size and func-tion. In the VD view of a normal Amazon parrot, thecardiac silhouette as measured across the heart baseat the level of the atria is about 50% of the width ofthe coelomic cavity measured at the fifth thoracicvertebra (Figure 12.1). The lateral margins of a nor-mal heart and liver in psittacine birds create anhourglass shape (Figure 12.1). In macaws, there isnormally a ventrally directed kink between the heartand liver in the lateral view (Figure 12.35).
Radiographic Evidence of Cardiac DiseasePrimary cardiac disease is rare, although congenitaldefects are occasionally detected on postmortem ex-amination. Congenital and viral diseases should beconsidered in juvenile birds with cardiac murmurs,exercise intolerance and cardiomegaly. The latter isusually accompanied by other systemic changes. Sec-ondary cardiac disease is more common. Pericardialeffusion is recognized radiographically as a symmet-rical, globoid enlargement of the cardiac silhouetteand may occur in birds with chlamydiosis, polyoma-virus, tuberculosis and neoplasia (Figure 12.63).
With cardiomegaly, heart enlargement is usuallyasymmetrical. Cardiomegaly may be caused by car-diomyopathy secondary to poxvirus (reported in ma-caws12), myxomatous valvular degeneration, endo-carditis (particularly secondary to pododermatitis),hemochromatosis, chronic anemia and compressionfrom extrinsic masses (see Chapter 27). Elongation ofthe heart shadow, loss of the caudal and cranialwaists, loss of indentation at the junction betweenthe heart and liver lobes and an increase in transa-trial dimensions indicate an increase in cardiac size.
Microcardia is associated with hypovolemia due toacute volume loss or endotoxic shock (see Figure21.2). There is retraction of the heart from betweenthe liver lobes, a more angular appearance to thecardiac shape and decreased transatrial size. What-ever the etiology, microcardia suggests a criticalstate, and appropriate volume replacement should beinstituted immediately.
Atherosclerosis with mineralization will result inprominence of the great vessels and may cause anincreased density of the caudal lung field. Althoughseen most often in older birds on high-fat diets, se-
vere vascular changes may occur in young birds.Acute myocardial infarcts, syncope and seizures (per-haps due to hypoxemia) have been described in birdswith atherosclerosis in the absence of radiographiclesions.
Respiratory System
Radiographic AnatomyThe radiographic changes associated with respira-tory disease are often subtle, and high quality radio-graphs are necessary to detect these lesions (Table12.1). The trachea in toucans and mynah birds devi-ates ventrally at the level of the thoracic inlet (seeFigure 47.3). Radiographically, the normal syrinx isdifficult to visualize but lies between the second andthird thoracic vertebrae in most birds (Figure 12.3).The heart covers much of the lung field in the VDview and only the caudal edge of the lungs can bevisualized (Figure 12.35). In normal birds, the bor-ders of the air sacs cannot be distinguished.
Lung parenchyma appears as a honeycombed struc-ture with the majority of the air densities repre-senting an end-on view of parabronchi (Figure12.35). The bronchioles can be visualized as trans-verse, indistinct, linear structures on the ventrodor-sal radiograph. Air bronchograms and atelectasis,which occur in mammals with pulmonary disease, donot occur in birds because of their unique lung anat-omy (a network of inter-connecting tubules with thelungs adhered to the thoracic wall).12 Bacterial orfungal infections are the most common cause ofpathologic abnormalities involving the respiratorytract. Chronic nasal discharge, periorbital swellingand soft tissue masses are indications for radio-graphs of the nasal cavity and infraorbital sinus.
TABLE 12.1 Radiographic Lesions of the Respiratory System
Radiographic Evidence of Respiratory DisordersHypovitaminosis A may cause an accumulation ofcaseous exudate that appears as a soft tissue opacitywithin the sinus without bone destruction. Soft tis-sue swelling with osteolysis of the calvarium is oftenassociated with osteomyelitis due to aspergillosis ormycobacteriosis. Air-filled swellings from distentionof the cervicocephalic air sacs may be caused byinfection, granulomas or idiopathic obstruction andshould be differentiated from subcutaneous emphy-sema, which is more diffuse.27
Changes in tracheal diameter may be caused by in-trinsic or extrinsic masses, stricture or stenosis. In-traluminal soft tissue masses or undulating soft tis-sue plaques may be caused by bacteria, hypo-vitaminosis A, parasites, fungi, foreign body or neo-plasm. A solitary mass in the syrinx may cause se-vere obstructive, open-mouthed dyspnea with no ob-vious radiographic changes. Superimposition of thegreat vessels, ribs and soft tissue over the syrinxcompromises interpretation. A subtle increase in softtissue in this region or fluid accumulation in thedistal trachea suggests obstruction. Although con-trast tracheography may help delineate somemasses, tracheoscopy is less stressful to the patientand more definitive (Figure 12.47).
Soft tissue surrounding the distal trachea is usuallyapparent. Tracheal strictures secondary to traumafrom fight-induced injuries or cuffed endotrachealtubes occasionally occur. Tracheal stenosis and de-formity of the tracheal rings are uncommon. Peritra-cheal masses may occur in the thoracic inlet due tothyroid enlargement secondary to goiter or neoplasm(Figure 12.45). Thyroid masses are usually well de-fined with smooth margins. Aspergillus sp. granu-loma encasement of the syrinx often causes a hoarse-ness in vocalization and slow, progressive respiratorydistress (Figure 12.46).
With pulmonary disease, the normal honeycombedpulmonary parenchyma may be enhanced by para-bronchial infiltration causing prominent ring shad-ows obliterated by filling of the parabronchial lumenwith fluid or caseous exudate or replaced by neoplas-tic or granulomatous infiltrates (see Table 12.1).Pneumonia often causes a prominent parabronchialpattern in the hilum and mid-portion of the lungs(Figure 12.47). As pneumonia progresses, the air-filled parabronchial lumen is replaced with caseousexudate, causing a blotchy mottled appearance to thelungs. This change is common at the caudal aspectsof the lungs and is best detected on VD radiographs.
Pulmonary edema and hemorrhage have a more dif-fuse appearance (Figure 12.50). Discrete, well de-fined masses are usually abscesses, granulomas ortumors (Figure 12.49).
The size of the air sacs will vary between inspiration(increased) and expiration (decreased). Additionally,the lung architecture will be more apparent on inspi-ration. Air sac disease may cause a barrel-shapedappearance to the thorax (Figure 12.51). Consoli-dated or thickened air sacs are not as compliant asnormal air sacs, causing the inspired air to be depos-ited in a relatively fixed cavity.
Radiographic changes indicative of inflamed air sacsinclude diffuse thickening, nodular infiltration orconsolidation. Fine lines across the air sacs with mildincreased opacity indicate thickening and are bestdetected on the lateral radiograph (Figure 12.52).The loss of visualization of abdominal viscera, blend-ing of the air sacs, blending of the interfaces betweenair and soft tissue and a hazy heterogeneous appear-ance to the air sacs are suggestive of consolidation(Figures 12.53, 12.54). Hyperinflation of the air sacsin combination with a radiolucent appearance sug-gest air trapping due to obstructed flow or abnormalcompliance.
Subcutaneous emphysema may result from trau-matic rupture of an air sac or as a complication ofendoscopy (see Chapter 22). Fractures of the coracoidor ribs may penetrate the air sacs, causing emphy-sema.
Coelomic Cavity and Gastrointestinal System
Radiographic AnatomyThe crop is present in the right lateral thoracic inletarea on the VD view. It may extend to varying de-grees across the midline depending on the presenceof ingesta and the species of bird (Figure 12.71,12.74). The thoracic portion of the esophagus canusually be differentiated on the VD and lateral radio-graphs. The cervical portion of the esophagus cannotbe distinguished without contrast media.
The proventriculus lies dorsal to the liver on thelateral view (Figure 12.35). The left lateral border ofthe proventriculus may be difficult to distinguishfrom the left lateral edge of the liver on the VD view.If the liver is of normal size, the proventriculusshadow will lie slightly lateral to the liver on the VDview. If the ventriculus contains radiodense material,it can generally be viewed on both the VD and lateral
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radiographs in its normal location, caudal and ven-tral to the proventriculus.
The position of the intestinal tract is widely variablebut it generally occupies the caudal, dorsal abdomi-nal cavity (Figure 12.72). The cloaca may or may notbe visualized, depending on its contents. The sum-mation between the liver and proventriculus on theVD view should not be misinterpreted as pathology(Figure 12.35). The duodenal loops lie to the right ofthe ventriculus in the VD view (Figure 12.72).
SpleenIf detectable on the VD radiograph, the spleen will benoted as a slightly oblong, rounded structure to theright of midline between the proventriculus and ven-triculus. On the lateral view, the spleen, if visible,overlaps the caudal end of the proventriculus andmay be slightly dorsal to it (Figure 12.35). Suggestednormal spleen sizes include: budgerigar = 1 mm,African Grey Parrot or Amazon parrot = 6 mm, Um-brella Cockatoo = 8 mm. The spleen of a pigeon iselongated or bean-shaped. In many other species it isspherical. Splenomegaly may be caused by infec-tious, neoplastic or metabolic diseases (Figure12.62), (Table 12.2).
LiverThe liver does not normally extend beyond the ster-num on the lateral radiograph (Figure 12.35). Inpsittacine birds, the liver should not extend laterallypast a line drawn from the coracoid to the acetabu-lum. The size of the hepatic silhouette can best bedetermined by making measurements of a VD radio-graph taken on inspiration. The distance is meas-ured in millimeters from the mid-sternum to thelateral-most aspect of the ribs at the base of theheart. This measurement is referred to as the ster-nal/rib distance (SR). This distance is divided byone-half and should be equal to the width of the rightliver as measured at the base of the heart. The sizeof the right liver is determined by measuring fromthe mid-sternum to the edge of the liver at the baseof the heart. If the actual measurement of the liver isgreater than its anticipated size as determined bythe SR value, then the liver is considered enlarged. Ifthe actual measurement of the right liver is less thanits anticipated size as determined by the SR value,then the liver is considered to be reduced in size(Harrison GJ, unpublished).
The liver in macaws and cockatoos frequently ap-pears to be reduced in size (Figure 12.58). The impor-tance of this finding remains undetermined; how-
ever, many birds with microhepatia are being fedseed diets that may or may not be supplemented withfruits and vegetables. Many affected birds have ab-normally low populations of gram-negative bacteria,low bile acids levels and elevated LDH, AST and GGTactivities. The CPK may be normal or elevated (Har-rison GJ, unpublished). The pesticide residues thatare present in most commercially available foodsmay play a role in the high incidence of hepatopa-thies in companion birds and should be addressed inbirds with microhepatia. In obese pigeons, the liverwill appear enlarged, which will resolve when thebirds are fasted.
The liver is frequently involved in systemic disease,and hepatomegaly is a common radiographic finding.Symmetrical enlargement of the liver lobes is mostcommon and is usually associated with infectiousand metabolic processes (Table 12.2). Neoplasms andgranulomatous diseases can cause asymmetrical en-largement of the liver.
Radiographic changes associated with liver enlarge-ment are loss of hourglass waist in the VD view,rounding of liver lobe margins, compression of ab-dominal air sacs, extension of the liver lobes beyondthe scapula/coracoid line, cranial displacement of the
TABLE 12.2 Differential Diagnosis for Hepatomegaly, Splenomegaly and Nephromegaly
Neoplastic Primary (biliary adenocarcinoma, hepatocellularcarcinoma, fibrosarcoma, hemangiosarcoma,hepatoma and lymphoma) and Metastatic(adenocarcinoma, fibrosarcoma and melanoma)
Parasitic Toxoplasmosis (mynahs), Sarcocystis sp., flukes(cockatoos) and Plasmodium sp.
Metabolic Lipidosis, fatty degeneration, hemochromatosis(mynahs and toucans) and gout
Splenomegaly Etiologies
Infectious Chlamydial, viral, bacterial and mycobacterial
heart, dorsal elevation of the proventriculus andcaudodorsal displacement of the ventriculus (Figure12.1, 12.60).13 A dilated, fluid-filled proventriculusmay appear radiographically similar to hepa-tomegaly, and a careful assessment of the VD viewcan be used to differentiate between these lesions.
PancreasRadiographic changes involving the pancreas arerare, although diminished contrast in the right cra-nial abdomen due to sanguineous exudate from acutenecrotizing pancreatitis has been reported. Pancre-atic masses are uncommon; however, space-occupy-ing lesions in the right cranioventral abdomen mayinvolve the pancreas, and large pancreatic cysts dooccur.
Gastrointestinal TractThe specific areas of the gastrointestinal tract arebest visualized through barium contrast examina-tion. The presence of gas, change in position andabnormal distention suggest a disease process. Al-tered gastrointestinal motility causing uniform orsegmental dilatation can be due to functional or me-chanical ileus.
Birds do not normally have gas in the intestinaltract, and any gas should be considered abnormal.Aerophagia can occur secondary to severe respira-tory disease or is frequently seen as an artifact of gasanesthesia (Figure 12.69). Distended, fluid-filledbowel loops should be considered abnormal except inmynah birds and toucans.
Inflammation, infection, foreign bodies, parasites,intussusception, stricture, granuloma and neoplasiamay cause intraluminal obstruction and segmentalincreases in the diameter of the gastrointestinaltract lumen secondary to excess gas and fluid accu-mulation. Extraluminal masses such as neoplasm,abscesses, eggs and cysts may compress the gastro-intestinal tract and cause changes similar to intralu-minal obstruction.
Uniform distention of the gastrointestinal tract ismost commonly associated with functional ileus dueto viral or bacterial infections, toxicity (eg, heavymetals), septicemia, hypoxemia, peritonitis or anes-thesia. Distention of the ingluvies, proventriculus orventriculus may be due to a localized process orobstruction within the intestines. A barium contraststudy is indicated for complete evaluation of theintestinal tract.
The cloaca may be distended from a retained soft-shelled egg, papilloma, cloacalith, neoplasm or idi-opathic atonic dilatation (Figure 12.70). Atonic dis-tension of the cloaca may occur with spinal traumaand infiltrative neoplasms involving the sacralnerves.
Abdominal masses usually cause a change in thelocation of the gastrointestinal tract. Hepatomegalyusually causes dorsal displacement of the proven-triculus and caudodorsal displacement of the ven-triculus. Splenic, testicular, ovarian and renalmasses compress the gastrointestinal tract ventrallyand either cranially or caudally. Adhesions due toinflammatory or septic peritonitis from rupturedeggs or perforation can also result in displacement ofthe gastrointestinal tract (Figure 12.67).
Abdominal effusion is associated with liver disease,neoplasia, metabolic disorders, sepsis, inflammationand cardiac failure. Fluid results in a homogeneousappearance to the intestinal peritoneal cavity (IPC)and obscures visualization of specific organs (Figure12.67). Consolidating air sacculitis can appear ra-diographically similar to fluid in the IPC in the lat-eral view, but differentiation is possible in the VDradiograph. If a pathologic process is occurringwithin the air sacs, specific organs within the intes-tinal peritoneal cavity will be definable in the VDview. If the fluid is within the IPC, there will still bea homogeneous appearance to the region of the vis-cera, and the air sacs will be compressed (Figure12.67). Fluid accumulation in the IPC may compressthe liver ventrally and displace the proventriculusand ventriculus cranially.
Urogenital System
The anatomy and physiology of the avian kidneysprevent the radiopacity that is characteristic ofmammalian kidneys. The kidneys are attached to thesynsacrum, are flattened dorsoventrally and havesmoothly rounded cranial and caudal divisions (Fig-ure 12.35).
The kidneys are best visualized in the lateral view.Because the renal silhouettes are superimposed, lat-eral oblique views may be necessary to distinguisheach kidney. The cranial division of the kidney pro-trudes from the pelvic brim, and the caudal divisionmay also be visualized on the lateral view. The kid-neys are generally not visible on the VD view, al-though the rostral edge of the cranial division canoccasionally be seen. If the kidneys are enlarged or
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increased in opacity, they may be more readily visu-alized in the VD position. The length of a normalAfrican Grey Parrot kidney is about 3 cm on thelateral view. In the Umbrella Cockatoo, the sug-gested normal kidney size is 3 cm x 0.7 cm. Thekidneys are normally surrounded by air, and loss ofthe air shadow indicates renal enlargement, dorsaldisplacement of abdominal organs or the presence ofabdominal fat or fluid (Figure 12.56).
Bilateral symmetrical nephromegaly results in a di-minished abdominal air sac space surrounding thekidneys and occurs with infection, metabolic disease,dehydration, post-renal obstruction and lympho-reticular neoplasia. Dehydration may also be associ-ated with increased renal density (see Figure 21.2). Alocalized enlargement with irregular borders is mostcommonly associated with a neoplasm, although ab-scesses may appear radiographically similar (Figure12.57).
Most renal tumors are locally invasive and usually donot metastasize. A solitary mass with smooth, welldefined margins is suggestive of a cyst; however,biopsy is the only definitive way to differentiate cysts,neoplasms and abscesses. Intravenous excretory uro-graphy is necessary to confirm renal disease whensevere nephromegaly obliterates the air space andcreates a positive silhouette sign with other viscera.
Masses involving the spleen, oviduct, testicles, ovaryand intestines may occupy space in the caudodorsalabdomen and mimic renal lesions (Figure 12.62). Thetestes of a reproductively active male are easily dis-tinguishable and should not be misinterpreted asrenal enlargement.
Testicular abnormalities causing radiographic signsare uncommon. Occasionally tumors cause testicularenlargement, and functional sertoli cell tumors maycause polyostotic hyperostosis. Orchitis is most easilydiagnosed through laparoscopy, and radiographicallycannot be distinguished from physiologic hypertrophy.
In a hen, an active ovary resembling a bunch ofgrapes may be apparent cranial to the kidneys, andan increased soft tissue opacity in the caudodorsalabdomen just ventral to the kidneys represents theoviduct (Figure 12.64). The most common radiog-raphically detectable abnormalities involving the fe-male genital tract are retained eggs, cystic oviductand egg-related peritonitis.
Mineralized eggs are easily visualized and often lo-cated in the terminal oviduct. Multiple eggs may be
present, and eggs may be free in the coelomic cavitydue to reverse peristalsis or oviductal rupture. Soft-shelled eggs are difficult to differentiate from otherabdominal masses, and ultrasound may aid in thediagnosis (Figure 12.66).
Hyperestrogen syndrome is common in budgerigarsand is characterized by an enlarged, distended ovi-duct, medullary hyperostosis, diminished abdominaldetail, visceral displacement, abnormal attempts ategg formation and abdominal hernia (Figure 12.65).14
Egg-related peritonitis can be difficult to discernfrom other causes of abdominal effusion. Cessation ofegg laying, weight loss and abdominal distention ina hen with a history of chronic egg laying are sugges-tive of egg-related peritonitis. Abdominocentesis andultrasound can be used to differentiate betweencauses of abdominal fluid (Figure 12.67).
Contrast Procedures
Administration of contrast agents can be used toenhance visualization of intraluminal abnormalitiesinvolving the gastrointestinal tract, respiratory sys-tem, cardiovascular system and subarachnoid space,and provides a qualitative assessment of function.Contrast agents used in mammals are consideredsafe in birds, although limited studies have beenperformed to assess specific contrast media reac-tions.6,14
The presence of concurrent disease and a patient’sage, size and state of hydration should all be consid-ered prior to initiating a contrast study. Severelydebilitated and seriously ill birds should be stabilizedand any fluid and electrolyte imbalances correctedprior to the study. Contrast studies are often stress-ful because of the number of radiographs required,and sedation is contraindicated in studies involvingthe gastrointestinal tract because of its effect ongastrointestinal motility. If anesthesia is used, it willslow the passage of contrast media, which should notbe misinterpreted as a pathologically induced de-crease in transit time.
Gastrointestinal studies are the most frequently per-formed contrast procedures in birds. They are usefulin delineating the position, structure and function ofthe gastrointestinal tract and associated organs.
Indications for barium follow-through examinationare acute or chronic vomiting or diarrhea that isnonresponsive to treatment, abnormal survey radio-graphic findings suggestive of an obstructive pat-tern, unexplained organ displacement, loss of ab-dominal detail suggesting perforation, hemorrhagicdiarrhea, history of ingestion of foreign material andchronic unexplained weight loss.11 Dehydrated birdsshould be rehydrated before administration of con-trast media to prevent the material from formingconcretions within the gastrointestinal tract.
Gastrointestinal motility may be altered by patho-logic conditions, stress and medications. Any drugsthat may alter motility such as tranquilizers, anes-thetics and anticholinergics should be discontinuedfor twenty-four hours prior to the gastrointestinalcontrast study. The age, size, diet and condition of thepatient will all affect gastrointestinal transit time.Faster transit times occur in small birds on soft diets.Passage is slowed in large seed-eating birds, obesebirds, in neonates on soft diets and in anesthetizedbirds.
Obtaining survey radiographs prior to beginning aprocedure will ensure proper technique as well asprovide a method of re-evaluating any changes in theradiographic pattern that may influence the study.The best contrast study can be performed when thegastrointestinal tract is empty. Excess fluid in theingluvies should be removed with a gavage tube priorto the administration of contrast media. The pres-ence of ingesta or fluid interferes with the quality ofthe study and may obscure lesions. Usually, a four-hour fast is adequate for emptying of the gastrointes-tinal tract without placing undue stress on smalleravian species. The gastrointestinal tract may beempty at the time of presentation in birds that areregurgitating.
Commercial barium sulfate suspensions provide thebest studies. Chemical grade barium is difficult tomix properly and may flocculate. If perforation of thegastrointestinal tract is suspected, an organic iodineis recommended; however, these preparations arehypertonic and can cause dehydration, especially insmall patients. Additionally, organic iodines are hy-
droscopic and are rapidly absorbed from the gastro-intestinal tract. Dilution of the contrast mediumwith intraluminal fluid may compromise the studyand interfere with defining the region of perforation.These agents do not coat the mucosa like barium doesand are not recommended for routine gastrointesti-nal examinations.
In juvenile birds, barium should be warmed prior toadministration. This is not necessary with adultbirds. To administer barium, the head and neck areextended and a soft, flexible feeding tube is passedinto the crop (see Figure 15.6). Small species do notrequire a speculum for passage of the tube; however,larger species need the beak held open either with aspeculum or gauze. Measuring the distance from thebeak to the crop and marking the tube helps ensurethat the tube is within the crop and not accidentallypassed into the tracheal lumen. The tube should bepalpated within the crop prior to the administrationof contrast material.
The dose of barium sulfate varies depending on thespecies and presence or absence of a crop, and rangesfrom 0.025-0.05 ml/g body weight, with the lowerdose range used in larger species. Lesions in themucosa are best identified by using a higher dose,and a lower dose can be used if the intention is tosimply identify borders of the gastrointestinal tract.
The contrast media should be administered slowlyuntil the crop is comfortably distended. Placing afinger over the distal portion of the cervical esopha-gus may help prevent reflux of barium sulfate whileit is being administered. Placing excessive pressureon the full crop may induce regurgitation. Slow re-moval of the tube may also help reduce reflux. If anyregurgitation occurs, the administration of contrastmedia should cease in order to reduce the risk of
CL INICAL APPL ICAT IONSRadiographic abnormalities that may be defined by gastrointes-tinal contrast studies include:
Change in location, size or shape of abdominal organs
Differentiation between the gastrointestinal tract and otherorgans
Altered motility (increased or decreased)
Increased or decreased luminal diameter
Mucosal irregularities
Filling defects
Changes in wall thickness
Extravasation of contrast media
Dilution of contrast with mucus or fluid
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pulmonary aspiration (see Chapter 22). Barium hasbeen used for bronchography in non-avian speciesbecause it is less irritating than other contrastagents.25 It is the volume of barium inhaled into therespiratory tract and not the agent itself that maycause problems.
Radiographic sequence may vary depending on thespecies and condition under investigation; however,in general, radiographs should be taken immediatelyafter administration of contrast media and at 0.5-, 1-,2-, 4-, 8- and 24-hour intervals (Table 12.3). Thetemporal sequence may vary if a lesion is identifiedduring the study.
If the crop is the only area of concern, a doublecontrast ingluviography may be performed in asso-ciation with a barium follow-through study or as aseparate procedure. Double contrast studies allowenhanced visualization of the crop wall for irregulari-ties such as thickening, mucosal defects, masses andthe detection of foreign bodies that may be obscuredby a single-phase contrast study. The total volume ofcontrast to be administrated (0.025 ml/g) is deter-mined. Half of the total volume is given as air and therest as barium. The air should be administered firstto prevent air bubbles from forming within the con-trast media. Although double contrast cloacographycan also be performed, direct visualization with en-doscopic equipment or an otoscope is preferable (Fig-ure 12.70).
Contrast Study FindingsDelayed transit time may be caused by functional ormechanical ileus. Mechanical ileus, depending on thelevel of obstruction and degree of luminal compro-mise, usually causes segmental dilation of the gas-trointestinal tract. Functional ileus usually causes auniform distention of the gastrointestinal tract (see
Figure 32.22). Mechanical obstruction occurs withintraluminal or extraluminal masses, foreign bodyingestion, helminthiasis and stricture. Intraluminalmasses such as neoplasm, abscess, granuloma, intus-susception and papilloma will cause filling defectswithin the contrast column (see Figure 25.15). Mu-cosal irregularity and ulceration may aid in differen-tiating neoplasia from more benign processes, butfungal disease and neoplasia can be difficult to dis-tinguish radiographically, and biopsy is the only de-finitive method to differentiate these diseases. Ex-traluminal masses involving the thyroid gland,spleen, gonads, oviduct or kidney may compress thelumen of the gastrointestinal tract and cause alteredmotility or obstruction.
Functional ileus occurs most frequently withneuropathic gastric dilatation and most often in-volves the proventriculus and ventriculus, althoughportions of the intestines may also be involved (seeFigure 32.24).11 Neurotoxins such as lead, inflamma-tory processes involving the coelomic cavity, severeenteritis and anesthetics may cause functional ileus.
Displacement of the gastrointestinal tract may occurwith organomegaly, accumulations of fluid in theintestinal peritoneal cavity, adhesions or hernia.Hepatomegaly causes dorsal elevation of the proven-triculus and caudal movement of the ventriculus.Splenic, gonadal and renal lesions may displace theintestines ventrally. Masses originating from the cra-nial division of the left kidney may push the ventricu-lus cranially. Adhesions associated with egg-relatedperitonitis may result in abnormal positioning ofportions of the gastrointestinal tract, with a fixedappearance and changes in luminal diameter. Her-nias, usually in hens, cause caudoventral displace-ment of the gastrointestinal tract.
A change in luminal diameter and wall thicknessmost often occurs with obstruction or functionalileus. Fungal diseases and neoplasia can cause nar-rowing of the lumen due to mural infiltration. In-flammatory changes can also increase wall thicknessand influence motility (see Figure 36.31). Mucosaldefects are most pronounced with aggressive dis-eases such as neoplasia or fungal infections. Spicula-tion of the contrast column due to a hyperemic mu-cosa, stringing out of barium from mixing withmucus, diminished bowel distensibility and in-creased transit times occur with inflammation (seeFigure 19.12).
TABLE 12.3 Barium Sulfate Transit Times*
Stomach SmallIntestines
LargeIntestines Cloaca
African Grey Parrot 10-30 30-60 60-120 120-130
Budgerigar 5-30 30-60 60-120 120-240
Racing pigeon 5-10 10-30 30-120 120-240
Indian Hill mynah 5 10-15 15-30 30-90
Hawk 5-15 15-30 30-90 90-360
Amazon parrot 10-60 60-120 120-150 150-240
Canary 5 10-15 15-30 30-90
Pheasant 10-45 45-120 120-150 150-240
*Time in minutes for barium sulfate administered by crop gavage to reach andfill various portions of the GI tract.
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Extravasation of contrast media occurs most oftenwith foreign body perforation, although metal feed-ing tubes or inflexible catheters can result in iatro-genic perforation of the gastrointestinal tract if im-properly used. Mural erosion in association withneoplasm, abscess or granuloma are less frequentcauses of perforation (see Figure 25.14). If a perfora-tion is suspected, an organic iodine contrast agent isrecommended to prevent contamination of thecoelomic cavity with barium.
Repeatability of a lesion on multiple views is impor-tant when attempting to identify intraluminalmasses. Gas bubbles and ingesta can create artifactsthat mimic mucosal defects and can lead to an incor-rect diagnosis. Tailoring the study to the individualpatient and obtaining additional views during thestudy will aid in accurate interpretation.
Intravenous Excretory Urography
In birds, the absence of a urethra, bladder, renalpelvis or division between the medulla and cortex, aswell as the glomerular filtration rate, tubular resorp-tion and the renal portal system make contrast uro-graphy of limited value. The primary indication forintravenous excretory urography is in defining masslesions associated with the urinary tract or delineat-ing the size and shape of the kidneys if they cannotbe adequately visualized on routine radiographs(Figure 12.55).14 Excretory urography may also havesome application for diagnosing functional disorders.Excretory urography should not be attempted in pa-tients with dehydration or debilitation or if renalfunction is severely compromised.
Sodium diatrizoate (680 mg of iodine/kg), iothalamatesodium (800 mg of iodine/kg) or meglumine diatrizo-ate (800 mg of iodine/kg) have been used for urogra-phy in birds with no observable adverse effects.6,14
These organic iodines should be warmed prior toadministration through the ulnar, jugular or medialmetatarsal veins. Radiographs are taken immedi-ately after contrast administration and at one-, two-,five-, ten- and twenty-minute intervals using thesame technique developed for the survey radiograph.
Most diagnostic information is obtained within thefirst five minutes of the study (Figure 12.55). Theaorta, heart and pulmonary artery will be visualizedwithin ten seconds; kidneys and ureters in 30 to 60seconds; and cloaca in three to five minutes afteradministering the contrast media (Figure 12.55).7 Inthe nephrographic phases of the study, there is an
immediate, uniform opacification of the kidneyshighlighting their size, shape and contour. In thenormal kidney, the three divisions are readily dis-cernible. There is no pyelographic phase.
Mass lesions such as renal tumors and cysts causechanges in the size, shape and contour of the kidneysand are distinguishable from gonadal lesions be-cause of the contrast enhancement. Tumors are usu-ally solitary mass lesions with irregular margins andare best visualized in the lateral view. Cysts tend tohave smooth, well defined borders. Biopsy is neces-sary to definitively differentiate between tumors andcysts. Abnormalities of the ureters are rare, but theymay be compressed in birds with egg binding andcloacal or abdominal masses.1 Occasionally, cloacallesions may be outlined during urography.
Radiographic changes in the excretory urogram aremost striking when the renal disease is unilateralbecause the unaffected kidney is usually hypertro-phied. In contrast, obstruction of a ureter may in-crease the radiodensity of the ipsilateral kidney bydelaying the washout from the kidney. If urine con-taining contrast medium is discharged into a pool ofurine containing no contrast media, the opacificationwill be delayed and reduced. Because a large pool ofurine may be retained in a hydroureter and withhydronephrosis, late films should be taken when nocontrast media is noted on early radiographs.
If one kidney appears to be non-functioning, it isimportant to consider the urinary protein concentra-tion, cytologic features of sediment and the size of thecontralateral kidney. In acute renal failure, the ex-cretory function is rapidly and severely, but oftenreversibly, compromised. If the contralateral kidneyis hypertrophied, the absence of function on the op-posite side is probably chronic in nature (urolithiasis)and may even indicate agenesis of that kidney (seeFigure 21.4).
Positive Contrast Rhinosinography
Contrast studies of the nasal cavity and sinuses mayaid in evaluation of the upper respiratory tract; how-ever, CT has replaced these procedures in other spe-cies (Figure 12.38 to 12.40). A 15 to 20% organiciodine agent can be injected into the sinus, and thesame views recommended under skull radiographyare taken for evaluation. Reactions to the contrastagent include edema and periorbital swelling. At theend of the procedure, the media can be flushed out ofthe sinuses with sterile saline to decrease the amount
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of local irritation. Space-occupying masses such asneoplasms, abscesses or granulomas may cause anobstruction to the flow of contrast media (Figures12.42, 12.43). In normal psittacine birds, thereshould be communication between the infraorbitalsinus, nasal cavity, opposite sinus, periorbital regionand tympanic region (Figures 12.39, 12.40).12 In somePasseriformes, the sinuses do not communicate (Fig-ure 12.41).
Positive ContrastTracheography and Bronchography
Contrast studies of the lower respiratory tract shouldbe considered high risk because patients requiringthese procedures are usually experiencing seriousrespiratory compromise. Tracheoscopy is preferablein patients of sufficient size (300 g). Focal lesions inthe terminal trachea or at the tracheobronchial bifur-cation that are difficult to visualize on survey radio-graphs may be defined by contrast tracheography(Figure 12.47).12
Patients should be stabilized with oxygen therapyand a tube placed in an abdominal sac to provideoxygen and anesthesia. Birds should be anesthetizedfor these studies. Contrast media is administered viaa tube placed in the trachea. Small aliquots (approxi-mately 0.1 ml) of a non-ionic agent or propyliodoneshould be given at a time, and radiographs taken todetermine tracheal filling. A minimal amount of con-trast media will be needed if fluoroscopy can be usedto identify a foreign body.
Non-selective Angiography
Cardiac disease requiring definition by contraststudies is rare. Diseases such as cardiomyopathy,some congenital shunts and valvular disease may bedefined by angiography in some larger birds; how-ever, ultrasonography is being utilized with greaterfrequency in other species. Non-selective angiogra-phy has been used for defining the normal cardiacsilhouette and major vessels. The same agents usedfor urography can be injected as a single, rapid,intravenous bolus in the jugular or ulnar veins toenhance visualization of the heart and great vessels.A rapid film changer, cinefluoroscopy or videotapingis necessary to record the image.
Myelography
Assessment of back trauma or congenital defects mayrequire myelography. Patients must be anesthetized
for this procedure. The bird is placed in lateral re-cumbency and a 25 ga needle or smaller is carefullyinserted into the subarachnoid space. Cerebral spi-nal fluid will flow into the needle, and several dropscan be collected for cytology. A non-ionic contrastmedia (0.25 ml/kg) is slowly injected into the cerebel-lar medullary cistern. Routine radiographs of thespine are taken.
Alternative Imaging
Fluoroscopy
A fluoroscope can be connected via an image intensi-fier to a video camera that can be used to makereal-time recordings of organ movement. In birds,fluoroscopy is the best way to monitor the motility ofthe gastrointestinal tract. Patients can be placed in adarkened box to perform fluoroscopy. This techniquemay be particularly useful for detecting hernias, neo-plasms, proventricular dilatation, hypermotility,ileus and gastric ulceration. In a normal parrot givena bolus of barium sulfate by crop tube, the bariumwill fill the proventriculus and ventriculus in five toten minutes. The barium will reach the intestines in15 minutes. These findings suggest that unre-strained (reduced stress) birds have a faster gastro-intestinal motility time than is routinely reportedusing standard radiographic techniques.22
Ultrasound
Ultrasonography is an imaging technique thatmakes use of high frequency sound waves transmit-ted by a transducer that is in contact with the skin.The waves are transmitted through the tissues in theabdomen and the echoes are recorded by the receiv-ing transducer unit. The resistance to sound wavesdepends on the molecular structure of the tissue thatis being penetrated. If the sound waves encounterbone, most of the waves are absorbed and not re-flected. If the sound waves are transmitted throughair, most are reflected and not absorbed. In both ofthese cases, organs that lie behind these structureswill not be detected.
Ultrasound studies in birds are somewhat limited bypatient size and conformation and the presence of airsacs; however, in larger avian patients with abdomi-
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Radiographic Anatomyand Abnormalities
adiography is an extremely valuable diag-nostic tool in avian patients. Every avianclinician should be comfortable with ra-diographic techniques and interpretation
of radiographic findings. One of the challenges ofidentifying subtle changes in radiographs of birdsis the wide species variability in normal anatomicstructures. Radiographs and xeroradiographs ofthe Orange-winged Amazon Parrot, cockatiel, Bob-white Quail and Mallard Duck are provided to as-sist the clinician in developing a more complete un-derstanding of the unique anatomic structuresencountered in varying genera of birds. These radio-graphs were provided by Bonnie J. Smith andStephen A. Smith and are reprinted with permis-sion from Veterinary Radiology 31:114-124, 1990;32:87-95, 1991; 31:226-234, 1990; 32:127-134, 1991.
Following the initial radiographs that address nor-mal radiographic anatomy are case presentationsdemonstrating characteristic radiographic changesassociated with pathology in various organ sys-tems. The reader is encouraged to compare the ra-diographic findings in these cases with the normalradiographs and xeroradiographs presented in thefirst section. Additionally, radiographs detailingchanges associated with specific organ systems canbe found in respective sections throughout the book.
R
FIG 12.1 Ventrodorsal xeroradiograph of a normal Orange-winged Amazon Parrot (courtesy of Bonnie J. Smith andStephen A. Smith).
1) trachea2) clavicular air sac3) pectoral muscle4) lung5) great vessels6) heart
7) normal hourglass constriction (“waist”) of heart-liver shadow 8) area of overlap of caudal thoracic and abdominal air sacs 9) area of spleen10) liver11) ventriculus with grit
12) intestines13) abdominal air sacs14) pygostyle15) pubis16) free caudal vertebra17) synsacrum18) periacetabular portion of ilium19) sternal rib
20) vertebral rib21) notarium22) sternum, ventral extremity of carina23) caudal extremity of scapula24) medial border of coracoid
25) ventral tubercle of humerus26) dorsal tubercle of humerus27) head of humerus28) should extremity of coracoid29) head of scapula30) clavicle
262
FIG 12.2 Ventrodorsal radiograph of a normal Orange-winged Amazon Parrot (courtesy of Bonnie J. Smith andStephen A. Smith).
263
FIG 12.3 Lateral xeroradiograph of a normal Orange-winged Amazon Parrot (courtesy of Bonnie J. Smith and Stephen A. Smith).
1) cervical vertebra2) coracoid3) scapula4) area of notarium5) vertebral rib
FIG 12.4 Lateral radiograph of a normal Orange-winged Amazon Parrot. 1) mesobronchus en route to abdominal air sac 2) crop containingingesta 3) spleen (courtesy of Bonnie J. Smith and Stephen A. Smith).
1) rhinotheca (superficial portion of arrow) covering premaxilla (lower portion of arrow) 2) mandibular symphysis 3) entoglossal bone of hypobranchial apparatus (hyoid) within the tongue 4) jugal arch (zygomatic arch) 5) ceratobranchial bone of hyoid 6) trachea 7) cervical rib 8) cervicocephalic air sac 9) retroarticular process of mandible10) cervical vertebra11) quadrate bone12) tympanic area13) cranial cavity14) caudal edge of orbit15) scleral ossicle16) rostral part of infraorbital sinus17) cere18) nasal aperture
FIG 12.5 Lateral xeroradiograph and ra-diograph of the head of a normal Orange-winged Amazon Parrot (courtesy of BonnieJ. Smith and Stephen A. Smith).
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FIG 12.6 Ventrodorsal xeroradiograph and radiograph of the head of a normal Orange-winged Amazon Parrot (courtesy of Bonnie J. Smithand Stephen A. Smith).
4) area of quadratomandibular joint (analogous to temporomandibular joint)5) caudal edge of cranium
6) trachea7) cervical rib8) cervicocephalic air sac
9) cervical vertebra10) ceratobranchial bone (hyoid apparatus)11) medial border of the left orbit
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1) cere 2) scleral ossicle 3) eyelid 4) jugal arch (zygomatic arch) 5) tympanic area 6) mandible 7) ceratobranchial bone of hyoid 8) trachea 9) cervicocephalic air sac10) cervical vertebra11) infraorbital sinus12) edge of cranium13) tongue (note paired entoglossum of hyoid)
FIG 12.7 Rostrocaudal xeroradiograph and radiograph of thehead of a normal Orange-winged Amazon Parrot (courtesy ofBonnie J. Smith and Stephen A. Smith).
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1) cere 2) tongue containing entoglossum of hyoid 3) scleral ossicle 4) ramus of mandible 5) ceratobranchial bone of hyoid 6) jugal arch (zygomatic arch) 7) cervical vertebra 8) cervicocephalic air sac 9) trachea10) edge of cranium
FIG 12.8 Oblique xeroradiograph and radiographof the head of a normal Orange-winged AmazonParrot (courtesy of Bonnie J. Smith and StephenA. Smith).
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FIG 12.9 Ventrodorsal xeroradiograph and radiograph of the wing of a normal Orange-winged Amazon Parrot (courtesy of Bonnie J. Smithand Stephen A. Smith).
1) clavicle 2) sternal extremity of coracoid 3) rib 4) scapula 5) head of humerus 6) ventral tubercle of humerus 7) extensor muscles of elbow 8) humerus 9) ventral condyle of humerus10) olecranon11) cotyles of ulna
12) ulna13) attachment of secondary flight feathers ot periosteum of ulna14) post-patagial membrane15) condyles of ulna16) ulnar carpal bones17) intercarpal joint18) minor metacarpal bone (MC III)19) minor digit (digit III) composed of one phalanx
20) major digit (digit II, composed of two phalanges)21) major metacarpal bone (MC III)22) alular digit (digit I)23) alular metacarpal bone (MC I)24) radial carpal bone25) distal extremity of radius26) radius27) extensor muscles of carpus and digit
28) propatagium (note feather follicles)29) head of radius30) dorsal condyle of humerus31) minor tubercle of humerus32) should extremity of coracoid33) cervical patagium34) mature feather with radiolucent core35) immature feather with vascular core (blood feather)
1) coracoid2) pectoral muscle3) flexor muscles to elbow4) humerus5) elbow joint, superimposition of radial head, olecranon and distal humerus
6) extensor muscles of carpus and digits 7) propatagium 8) radius 9) distal extremity of radius10) radial carpal bone
11) area of carpometacarpus12) alular digit (digit I)13) major and minor metacarpals (superimposed MC III and MC II)
14) major and minor digits (super imposed digit III and II)15) intercarpal joint16) extensor muscles of elbow17) shoulder joint18) head of scapula
FIG 12.10 Craniocaudal xeroradiograph of a wing of a normal Orange-winged Amazon Parrot. The wing has been slightly rotated to separatethe image, of the radius, ulna and alular digit (courtesy of Bonnie J. Smith and Stephen A. Smith). 269
FIG 12.11 Lateral xeroradiograph and radiograph of the pelvic limb of a normal Orange-winged Amazon Parrot (courtesy of Bonnie J. Smithand Stephen A. Smith).
1) ilium2) greater trochanter of femur super- imposed over femoral head3) femur4) patella5) femoral condyles6) proximal extremity of tibiotarsus7) body of tibiotarsus
8) condyles of tibiotarsus 9) cotyles of tarsometatarsus10) tarsometatarsus11) metatarsal I12) digit III (consists of four phalanges)13) digit II (consists of three phalanges)
14) digital pad15) digit IV (consists of five phalanges)16) digit I (consists of two phalanges)17) podotheca (note abrupt change in skin from delicate and feathered to thick and scaled)18) calcaneus
FIG 12.12 Craniocaudal xeroradiograph and radiograph of the pelvic limb in a normal Orange-winged Amazon Parrot (courtesy of BonnieJ. Smith and Stephen A. Smith).
1) neck of femur2) head of femur within acetabulum3) pubis4) femur
5) medial femoral condyle6) intercondylar sulcus7) proximal extremity of ti biotarsus8) fibula
9) tibiotarsus10) condyles of tibiotarsus11) intertarsal joint12) cotyles of tarsometa- tarsus
13) tarsometatarsus14) digit I15) tarsometatarsal trochlea for digit II16) digital pad
17) digit II18) digit III (four phalanges)19) digit IV20) metatarsal I
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1) trachea2) clavicular air sac3) pectoral muscle4) lung5) heart6) normal hour-glass constriction (“waist”) of the heart-liver shadow
7) area of overlap of caudal thoracic and abdominal air sacs 8) spleen 9) liver10) ventriculus11) intestines12) abdominal air sac13) pygostyle
14) pubis15) free caudal vertebra16) synsacrum17) sternum, ventral extremity of carina18) notarium19) caudal extremity of scapula20) medial border of coracoid
21) ventral tubercle of humerus22) head of humerus23) dorsal tubercle of humerus24) head of scapula25) shoulder extremity of coracoid26) clavicle
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FIG 12.13 Ventrodorsal xeroradiograph (facing page) and radiograph of a normal cockatiel (courtesy of BonnieJ. Smith and Stephen A. Smith).
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FIG 12.14 Lateral xeroradiograph and radiograph of a normal cockatiel (courtesy of Bonnie J. Smith and Stephen A. Smith).
1) cervical vertebra2) coracoid3) scapula4) area of notarium5) vertebral rib
FIG 12.15 Lateral xeroradiograph and radiograph of a normal Mallard Duck (courtesy of Bonnie J. Smith and Stephen A. Smith).
1) clavicle2) cranial margin of keel of sternum (note absence of concave curvature)3) feather follicles (note prominence characteristic of Anseriformes)
4) ventriculus containing grit5) pubis6) papilla of uropygial gland7) uropygial gland (note large size)8) intestines
9) abdominal air sac10) lung11) area of syrinx (note absence of bulla in the hen)
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1) clavicle2) shoulder extremity of coracoid base3) head of humerus4) feather follicle
5) heart6) liver7) lateral caudal process of sternum8) intestines
9) ventriculus containing grit10) caudal extremity of scapula11) left brachiocephalic trunk12) cavity of syringeal bulla
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FIG 12.16 Ventrodorsal xeroradiograph (facing page) and radiograph of a normal male Mallard Duck (courtesy of Bonnie J.Smith and Stephen A. Smith).
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FIG 12.17 Ventrodorsal radiograph of a clinically normal Trumpeter Swan. In this species, the tracheais lengthened and is permanently curved within an excavation in the sternum. The 1) trachea enters thethoracic inlet, 2) courses caudally within the sternal excavation and re-curves cranially near the caudalend of the sternum. 3,4) A small loop is formed within the sternal excavation, which is visible as an end-ontubular view, and the trachea then courses 5) cranially to the thoracic inlet, where it re-curves and entersthe syrinx (courtesy of Bonnie J. Smith and Stephen A. Smith).
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FIG 12.18 Lateral xeroradiograph and radiograph of a normal Mallard Duck (courtesy of Bonnie J. Smith and Stephen A. Smith).
1) nail2) mandibular symphysis3) tongue4) lamellae of bill
5) entoglossum of hyoid apparatus (note large size to support well developed tongue)6) rostral basibranchial bone of hyoid apparatus7) ceratobranchial bone of hyoid apparatus
8) trachea 9) epibranchial bone of hyoid apparatus10) atlas
11) scleral ring12) nasal aperture
FIG 12.19 Lateral xeroradiograph of the Chinese Goose demonstrating the 1) frontal knob. Note the bony core of this structure and itswell-developed soft tissue covering (courtesy of Bonnie J. Smith and Stephen A. Smith).
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FIG 12.20 Ventrodorsal xeroradiograph and radiograph of the head of a normal Mallard Duck. 1) upper bill covering premaxilla 2) mandible3) ceratobranchial bone of hyoid apparatus 4) scleral ring 5) epibranchial bone of hyoid apparatus 6) trachea (courtesy of Bonnie J. Smithand Stephen A. Smith).
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FIG 12.21 Rostrocaudal view of xeroradiographand radiograph of a normal Mallard Duck. 1)scleral ring 2) trachea 3) ceratobranchial bone ofhyoid apparatus 4) mandible 5) jugal arch (zygo-matic arch) (courtesy of Bonnie J. Smith andStephen A. Smith).
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FIG 12.22 Craniocaudal xeroradiograph (left) and mediolateralxeroradiograph (right) of the pelvic limb of a normal Mallard Duck(courtesy of Bonnie J. Smith and Stephen A. Smith).
1) patella2) condyles of femur3) fibula4) condyle of tibiotarsus5) cotyle of tarsometatarsus6) tarsometatarsal trochlea for digit IV7) distal phalanx of digit IV
8) lateral interdigital web 9) distal phalanx of digit III10) intermediate interdigital web11) distal phalanx of digit II12) distal phalanx of digit I13) metatarsal bone I14) proximal tibiotarsus
1) greater trochanter of femur2) femur3) patella, superimposed over keel4) cnemial crest of tibiotarsus5) condyles of tibiotarsus6) cotyles of tarsometatarsus7) podotheca (unfeathered skin covering pes)8) trochlea of tarsometatarsus9) distal (fourth phalanx) of digit III (note horny nail covering bony core)
10) interdigital web11) distal (fifth) phalanx of digit IV12) distal (third) phalanx of digit II13) distal (second) phalanx of digit I14) metatarsal bone I15) ossification within digital tendon16) fibula, superimposed with body of tibiotarsus
FIG 12.23 Ventrodorsal xeroradiograph of the wing of a normal Mallard Duck (courtesy of Bonnie J. Smith and Stephen A. Smith).
1) body of scapula2) ventral tubercle of humerus3) condyles of humerus4) olecranon of ulna5) condyles of ulna6) ulnar carpal bones
7) minor metacarpal bone 8) minor digit (consisting of one phalanx) 9) major digit (consisting of two phalanges)10) major metacarpal bone11) alular digit
12) extensor of alular meta- carpal bone13) radial carpal bone14) distal extremity of radius15) head of radius16) pectoral crest of humerus
17) head of humerus18) should extremity of coracoid bone19) clavicle
FIG 12.24 Craniocaudal xeroradiograph of the wing of a normal Mallard Duck (courtesy of Bonnie J. Smith and Stephen A. Smith).
1) clavicle2) coracoid bone3) pectoral crest of humerus4) condyles of humerus5) superimposed proximal radius and ulna6) distal extremity of radius
7) radial carpal bone8) alular digit9) superimposed major and minor metacarpal bones10) superimposed major and minor digits
11) distal extremity of ulna12) ulnar carpal bone superimposed over other carpal structures13) scapula
7) pubis 8) terminal process of ischium 9) postacetabular portion of ilium10) preacetabular portion of ilium11) synsacrum12) ventral extremity of carina (keel)
13) head of scapula14) ventral tubercle of humerus15) shoulder extremity of coracoid16) shoulder extremity of oviduct17) egg within magnum of oviduct
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FIG 12.25 Ventrodorsal xeroradiograph (previous page) and radiograph of a normal female Bobwhite Quail(courtesy of Bonnie J. Smith and Stephen A. Smith).
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FIG 12.26 Lateral xeroradiograph and radiograph of a normal female Bobwhite Quail. Note the short, heavy muscled, rotund body andcompact viscera. Differentiation between the heart and the liver is difficult (courtesy of Bonnie J. Smith and Stephen A. Smith).
1) trachea2) clavicle3) clavicle at point of fusion into furcula (note hooked shape)
4) sternal rib5) carina (keel)6) area of liver7) ventriculus containing grit
8) pubis 9) papilla of uropygial gland10) terminal process of ischium11) intestines
12) vertebral rib13) lung14) heart
15) coracoid16) follicle on ovary
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FIG 12.27 Lateral xeroradiograph and radiograph of the head of a normal Bobwhite Quail. 1) premaxilla 2) rhinotheca covering premaxilla3) jugal arch (zygomatic arch) 4) mandible 5) ceratobranchial bone of hyoid apparatus 6) cervical rib on cervical vertebra 7) caudal edge oforbit 8) scleral ring 9) rostral basibranchial bone of hyoid apparatus (courtesy of Bonnie J. Smith and Stephen A. Smith).
FIG 12.28 Ventrodorsal xeroradiograph and radiograph of the head of a normal Bobwhite Quail. 1) nares 2) ceratobranchial bone of hyoidapparatus 3) trachea 4) scleral ring 5) lacrimal bone 6) epibranchial bone of hyoid apparatus (courtesy of Bonnie J. Smith and Stephen A.Smith).
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FIG 12.29 Rostrocaudal xeroradiograph and radiograph of the head of a normal Bobwhite Quail. 1) lacrimal bone 2) scleral ring 3) jugalarch (zygomatic arch) 4) epibranchial bone of hyoid apparatus 5) trachea 6) ceratobranchial bone of hyoid apparatus 7) mandible (courtesyof Bonnie J. Smith and Stephen A. Smith).
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FIG 12.30 Ventrodorsal xeroradiograph of the wing of a normal Bobwhite Quail (courtesy of Bonnie J. Smith and Stephen A. Smith).
1) head of scapula2) ventral tubercle of humerus3) ulna4) ulnar carpal bone5) minor metacarpal bone
6) minor digit (consisting of one phalanx)7) major digit (consisting of two phalanges)8) major metacarpal bone9) alular digit
10) extensor process of alular meta carpal bone11) radial carpal bone12) sesamoid bone in tendon of tensor propatagialis
13) radius14) pectoral crest of humerus15) shoulder extremity of coracoid bone16) shoulder extremity of clavicle
FIG 12.31 Craniocaudal xeroradiograph of the wing of a normal Bobwhite Quail (courtesy of Bonnie J. Smith and Stephen A. Smith).
1) clavicle2) shoulder extremity of coracoid bone3) pneumatic foramen of humerus (point of entry of clavicular air sac)4) humerus
5) radius6) superimposed radial and ulnar carpal bones7) alular digit8) minor digit
9) distal phalanx of major digit10) superimposed major and minor metacarpal bones11) ulna12) scapula
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FIG 12.32 Craniocaudal xeroradiograph of the pelvic limb of a normal Bobwhite Quail (courtesyof Bonnie J. Smith and Stephen A. Smith).
FIG 12.33 Mediolateral xeroradiograph of the pelvic limb of a normal Bobwhite Quail (courtesyof Bonnie J. Smith and Stephen A. Smith).
1) tibiotarsus 2) metatarsal bone I 3) distal phalanx of digit I 4) podotheca 5) distal phalanx of digit II 6) distal phalanx of digit III 7) distal phalanx of digit IV 8) tarsometatarsal trochlea for digit IV 9) tarsometatarsus10) fibula11) patella12) greater trochanter of femur
1) patella2) cnemial crest of tibio- tarsus3) condyles of tibiotarsus4) tarsometatarsus5) podotheca6) distal (fourth) phalanx of digit III (note horny nail covering bony core)7) digital pads8) distal (fifth) phalanx of digit IV
9) distal (third) phalanx of digit II10) metatarsal pad11) distal (second) phalanx of digit I12) metatarsal bone I13) mineralized tendons of digital flexor muscles14) fibula, superimposed on body of tibiotarsus15) condyles of femur16) head of femur within acetabulum
FIG 12.34 Mediolateral xerora-diograph of the pes of a peacock.1) the calcarial process is theosseous core of the metatarsalspur or calcar. Note the hornysheath covering the process. 2)Note also the mineralization ofthe digital flexor tendons as wellas the 3) well-developed meta-tarsal and 4) digital pads in thisground-dwelling bird (courtesyof Bonnie J. Smith and StephenA. Smith).
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FIG 12.35 Low contrast radiographs of a Hyacinth Macaw demon-strating soft tissue structures: heart (h), spleen (s), liver (l), lung (lu),kidneys (k), proventriculus (p), ventriculus (v), ovary (o), intestines (i),contiguous area of the caudal thoracic and abdominal air sacs (a), bodymusculature (arrow) and right abdominal air sac (open arrow) (cour-tesy of Marjorie McMillan).
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FIG 12.36 A six-year-old Amazonparrot was presented with firm bi-lateral swelling surrounding theauditory meatus (arrows). Themasses were solid and attached. a)Surgical biopsy of the mass indi-cated chronic fibrosing cellulitis. b)The mass is easily visualized on anoblique view of the head (arrows).The tympanic area can also be visu-alized (open arrows). The masses re-solved when the bird was changedfrom an all-seed to a formulated diet.
292
FIG 12.37 Alexandrian Parakeet with lateral deviation of themaxillae. The deformity had been present since hatching. Theparents of this bird produced a defective neonate every four to sixchicks, suggesting that the problem was genetic in origin. Rostro-caudal radiograph showing dorsal displacement of the right pala-tine bone (arrow). Ventrodorsal radiograph showing lysis of theright palatine bone (arrow).
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FIG 12.38 Lateral positive contrast air sacculography demonstrating the extent ofthe cephalic air sac in a mature Blue-fronted Amazon Parrot. The cephalic portion(arrow) of the cervicocephalic air sac connects to the caudal aspect of the infraorbitalsinus (open arrow) (courtesy of Marjorie McMillan).
FIG 12.39 Lateral view of a rhinogramperformed on a normal Bare-eyedCockatoo showing the flow of contrastmedium from the nasal cavity (open ar-rows) through the choanae at the levelof the palate and into the nasopharynxand oral cavity (open arrow). Otherstructures include the mandible (m), zy-gomatic arch (z), ceratobranchial boneof hyoid (c) and tracheal tube (t) (cour-tesy of Elizabeth Watson).
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FIG 12.40 Positive contrast sinography in an adult cockatiel showingdrainage and interconnections of the infraorbital sinuses (courtesy ofMarjorie McMillan).
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FIG 12.41 Positive contrast sinography in a mynah bird showingminimal drainage of contrast medium in comparison to Psittacifor-mes. Additionally, there is not communication between the infraor-bital sinuses, and contrast medium injected into the right infraorbi-tal sinus remains localized (courtesy of Marjorie McMillan).
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FIG 12.42 A four-month-old African Grey Parrot was presented with a life-long history of persistent serous to mucopurulent nasal discharge.Antibiotic therapy would change the discharge from mucopurulent to serous but would not resolve the problem. On physical examination,it was noted that fluid introduced into the nostrils would not exit through the oral cavity. Lateral view of rhinogram indicating that contrastmedium moved ventrally through the nasal cavity (open arrow) and stopped abruptly at the level of the palate (closed arrow). Endoscopyindicated a persistent membrane covering the choana. Rostrocaudal radiograph following infusion of contrast medium into the right nostrilshowing communication between the infraorbital sinuses. Note that the contrast medium does not properly pass into the oral cavity in thisbird. Other structures of interest include the palatine bone (p), zygomatic arch (z), mandible (m), quadrate (q) and the periorbitaldiverticulum of the infraorbital sinus (s) (courtesy of Elizabeth Watson).
FIG 12.43 A four-year-old Umbrella Cockatoo was presented with a long history of bilateral oculonasal discharge. Fluidflushed into the nostrils failed to enter the oropharynx. A lateral rhinogram indicated that contrast medium movedthrough the nasal cavity (open arrows) and stopped abruptly at the level of the palatine (closed arrows) (courtesy ofElizabeth Watson).
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FIG 12.44 An adult male Satyr Tragopan Pheasant was presented with an acute onset of dyspnea and depression. Abnormal clinico-pathologic findings include PCV=23, SGOT=490, LDH=671. Radiographs indicate gaseous distension of the gastrointestinal tract (arrows)causing cranial displacement of other abdominal organs. Increased densities were noted in the syringeal area (open arrows), and the spleen(s) was enlarged. The bird did not respond to supportive care. Necropsy findings included pericarditis and granulomatous pneumonia andtracheitis. Heart (h), liver (l), lung (lu), ventriculus containing grit (v).
FIG 12.45 A two-year-old male cockatiel was presented for evaluation of a voice change and progressive dyspnea. A lateral radiographshowed a large, lobular, soft-tissue mass surrounding the distal trachea (arrows) that extended into the lung (lu) and displaced the trachea(t) ventrally. The liver (l) is also enlarged and is displacing the gas-filled proventriculus (p) dorsally. The histologic diagnosis was thyroidadenocarcinoma (courtesy of Marjorie McMillan).
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FIG 12.46 A Red-lored Amazon Parrot was presented with coughing and a voice change. Initial radiographs showed a large, soft-tissuemass (arrows) ventral to the trachea and syrinx. Radiograph taken 11 months after treatment with antifungal agents demonstratesresolution of the mass (courtesy of Marjorie McMillan).
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FIG 12.47 a) Lateral radiograph of a mature Blue-fronted Amazon with dyspnea. Abnormal findings included increased parabron-chial densities (ring shadows -r), hyperinflation of the air sacs and thickening of the contiguous wall of the cranial and caudal thoracicair sacs (open arrow). The ventral separation of the contiguous wall of these air sacs forms a distinguishable fork (f) with the cranialthoracic air sac coursing cranially and the caudal thoracic air sac coursing caudoventrally. An increased soft tissue density in thetrachea suggests a mass (arrow). b) Positive contrast study of the trachea using an oil-based contrast medium. The medium is passingdorsally across an intratracheal mass (arrows) (courtesy of Marjorie McMillan).
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FIG 12.48 An adult Blue-crowned Amazon Parrot was presented withnasal discharge and dyspnea. The increased parabronchial densities (openarrows) in the mid and caudal portions of the lung are suggestive ofpneumonia. Several thickened air sac walls are visible (arrows). Theintestines (i) are filled with gas secondary to aerophagia caused by severedyspnea. The right abdominal (ra) and left abdominal (la) air sac areas areclearly visible. The cloacal wall (c) is also evident.
301
FIG 12.49 A four-year-old lovebird with a round cell carcinoma of the wing and secondary metastasis to the lung (arrows) (courtesy ofMarjorie McMillan).
FIG 12.50 A five-year-old male budgerigar was presented for lethargy and dyspnea. Lateral radiographs indicate an air-filled crop (c)secondary to aerophagia. There is a uniform increase in the parabronchial pattern (arrows) and obliteration of the abdominal air sacspace due to bulging of the abdominal wall (open arrow). The homogenous appearance of the abdomen is due to a combination of effusionand a mass. The pulmonary pattern is consistent with edema, which responded to diuretic therapy (courtesy of Marjorie McMillan).
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FIG 12.51 A four-month-old Double Yellow-headed Amazon Parrotwas presented with a bilateral, purulent nasal discharge and dyspnea.Radiographs indicated parabronchial ring shadows (arrow) consistentwith pneumonia. Hyperinflation of the thoracic and abdominal airsacs and thickening of the air sac membranes are characteristic of airsacculitis (open arrows). Note the barrel shape of the body in the VDradiograph indicative of dyspnea. Cultures from the trachea werepositive for Klebsiella sp., and the bird responded to antibiotics. Liver(l), intestines (i) and spleen (s).
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FIG 12.52 A ten-year-old Green-winged Macaw was presented with exercise intolerance. Initial radiographs (top) indicated thickening oredema of the air sacs. Radiographs one month after the initiation of antibiotic therapy indicate a decrease in the soft tissue opacity of theair sacs. However, the presence of residual thickening (arrow) would warrant continuation of therapy. Spleen (s), proventriculus (p),ventriculus (v), heart (h), liver (l) (courtesy of Marjorie McMillan).
304
FIG 12.53 An African Grey Parrot with a soft tissue opacity in the left cranial and caudal thoracic air sacs (courtesyof Marjorie McMillan).
305
FIG 12.54 A Blue-fronted Amazon Parrot with a soft tissue plaque in the right abdominal air sac (arrows) (courtesyof Marjorie McMillan).
306
FIG 12.55 Excretory urogram in an African GreyParrot. The radiographs were taken 30 secondsafter the injection of contrast medium. The kidneys(open arrows) and ureters (arrows) are opacified.Note the rim of air that is normally present dorsalto the kidneys (courtesy of ME Krautwald).
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FIG 12.56 A Blue-crowned Amazon Parrot with neph-romegaly (arrows). The diminished serosal detail in thecoelomic cavity was caused by hemorrhage from the dis-eased kidney. The pathologic diagnosis was glomeru-lonephropathy, infarction and arteritis (courtesy of Mar-jorie McMillan).
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FIG 12.57 Sulphur-crested Cockatoo with nephromegaly(open arrows) and a perirenal granuloma (arrow) causedby aspergillosis. The severe air sac distension is causingthe liver (l) to appear reduced in size. Other structures thatare easy to identify include the heart (h), syrinx (s), lung(lu), proventriculus (p), ventriculus (v) and intestines (i)(courtesy of Marjorie McMillan).
309
FIG 12.58 A two-year-old Blue and Gold Macaw was presentedwith anorexia and mild dyspnea. Increased lung sounds werenoted by auscultation. Radiographs indicated microhepatiaand splenomegaly. It is common for the liver to be smaller thanexpected in macaws and some larger cockatoos. The importanceof a small liver in these birds has not been defined. Heart (h),liver (l), spleen (s), syrinx (s), proventriculus (p), ventriculus (v),gonad (g).
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FIG 12.59 An eight-week-old Sulphur-crestedCockatoo with nephromegaly (open arrows) and mas-sive hepatomegaly (arrows) caused by lipidosis. Notethat the normal air sac triangle above the proven-triculus is obliterated and the proventriculus (par-tially gas-filled) is being displaced cranially (courtesyof Marjorie McMillan).
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FIG 12.60 An adult male cockatiel was presented with weakness, a distended abdomen and harsh, moistrespiratory sounds. Radiographs indicated massive hepatomegaly (l) with cranial displacement of theheart (h), dorsal displacement of the proventriculus (p) and caudodorsal displacement of the ventriculus(v). A mild diffuse parabronchial pattern secondary to edema was also present. Histopathology indicatedsevere, chronic active hepatitis and cirrhosis (courtesy of Marjorie McMillan).
FIG 12.61 A ten-week-old Blue-fronted Amazon Parrot with a pal-pable abdominal mass was presented for anorexia and lethargy.Abnormal clinicopathologic findings included WBC=20,000 (4%bands), AST=12,420, LDH=8,000. Radiographs indicated hepa-tomegaly (l) with dorsal displacement of the proventriculus (p).Ultrasound confirmed the liver enlargement. Chlamydia sp. wasdetected in the bird’s excrement using an antigen capture ELISA,and the bird responded to therapy with doxycycline.
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FIG 12.62 A two-year-old Blue and Gold Macaw was presented with lethargy, anorexia and abdominal distension. Radiographs indicateda massive splenomegaly (arrow) and nephromegaly (curved arrow) caused by Chlamydia sp. The enlarged spleen is displacing theproventriculus (p) and ventriculus (v) ventrally and the liver (l) cranially (courtesy of Marjorie McMillan, reprinted with permission of CompCont Ed 8:1986).
FIG 12.63 A Blue-fronted Amazon Parrot was pre-sented with lethargy and exercise intolerance, inter-mittent episodes of panting and syncope. VD radio-graphs indicated a biatrial enlargement and a decreasein the cardiohepatic waist caused by cardiomegaly.Liver (l) (courtesy of Marjorie McMillan).
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FIG 12.64 Lateral radiograph of a Double Yellow-headed Amazon Parrot with an active ovary (arrow). Note the “grape-like” cluster offollicles cranioventral to the kidneys (k) (courtesy of Marjorie McMillan).
FIG 12.65 A female budgerigar was presented for evaluation of a ventral abdominal mass. A barium contrast study indicatedthat the mass was herniated intestines. Note also the increased density of the skeleton (polyostotic hyperostosis). Herniationand polyostotic hyperostosis are characteristic of hyperestrogenism (courtesy of Marjorie McMillan).
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FIG 12.66 Radiographs of an egg-bound cockatiel suggest the pres-ence of one large abnormally shaped egg and one smaller incompletelyformed egg. Ultrasound indicated the presence of four eggs (courtesyof Marjorie McMillan).
FIG 12.67 A mature cockatiel hen was presented for dyspnea and a swollen abdomen. Radiographs indicated a fluid-filledabdomen with cranial displacement of the ventriculus (v) and proventriculus (p), both of which are impacted with grit.Abdominocentesis was consistent with an exudative effusion, and the diagnosis was egg-related peritonitis. The cranialdisplacement of the abdominal viscera indicates that the fluid is present in the intestinal peritoneal cavity (courtesy of MarjorieMcMillan).
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FIG 12.68 A 35-year-old Yellow-headed Amazon Parrotwas presented with a firm ventral midline mass. Radio-graphs indicated rounding of the liver lobes and hepa-tomegaly (arrows). The mass was visible as a soft tissueopacity at the caudal edge of the sternum (open arrow). Anexploratory laparotomy revealed a herniated liver.Proventriculus (p), ventriculus (v) (courtesy of MarjorieMcMillan).
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FIG 12.69 A Blue and Gold Macaw was presented with severe dyspnea including a tail bob. The bird was sneezing and had both ocularand nasal discharges. The only abnormal clinicopathologic finding was WBC=18,000. Radiographic changes included gaseous distensionof the intestines (i), thickening of the contiguous membrane of the caudal thoracic and abdominal air sac (open arrow). The client was aheavy smoker, and the lesions resolved over a three-month period when the client quit smoking and the bird received daily exposure tofresh air and sunlight.
FIG 12.70 Contrast medium was injected into the gaseous distended cloaca of an Amazon parrot with severe dyspnea. Note the cranialdisplacement of the intestines (i) and ventriculus (v).
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FIG 12.71 Radiographs of an adult African Grey Parrot ten minutes after administering barium sulfate. Crop (c), thoracic esophagus(arrow), proventriculus (p), ventriculus (v) (courtesy of ME Krautwald).
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FIG 12.72 An Amazon parrot 20 minutes after bariumsulfate administration. Crop (c), thoracic esophagus (ar-row), proventriculus with filling defects (p), ventriculus(v), duodenum (d), ilium and jejunum (open arrow).
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FIG 12.73 Radiographs of an adult African Grey Par-rot 60 minutes after administering barium sulfate.Crop (c), thoracic esophagus (arrow), proventriculus(p), ventriculus (v), duodenum (d), intestines (i), colon(open arrow) (courtesy of ME Krautwald).
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FIG 12.74 Radiographs of an adult pigeon 20 minutes afteradministration of barium. Note the crop (c) is composed of twolateral compartments. Thoracic esophagus (arrow), proven-triculus (p), duodenum (d), colon (open arrow), cloaca (cl)(courtesy of ME Krautwald).
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FIG 12.75 An adult Amazon parrot was presented with a history of dyspnea and weight loss. A mass (arrow) was identified in thedorsocranial thorax. Barium contrast radiography indicated that the mass was associated with the thoracic esophagus. Radiograph a) wastaken 45 minutes and radiograph b) was taken 2 hours after barium administration. Contrast medium can be seen in the ventriculus (v),ascending and descending colon (d), jejunum and ileum (i), colon (open arrow) and cloaca (c).
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FIG 12.76 Two-week-old pigeon. Thegastrointestinal tract of neonates staysdistended with food, making the deline-ation of abdominal structures difficult.Note the large joint spaces charac-teristic of developing bones in birds (ar-rows) (courtesy of ME Krautwald).
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FIG 12.77 An adult swan was presented with inter-mittent lameness. The tibiotarsal joint was hot, firmand swollen. Radiographs indicated joint enlargement,subchondral bone lysis and erosion of the intercondylarspace. These lesions were suggestive of septic arthritis.Radiograph of the normal leg for comparison.
FIG 12.78 A fledgling Golden Eaglewas presented with an inability tostand and a decreased range of motionin both pelvic limbs. The bird had beenequipped with a radiotransmitter andreleased from a hack tower severalweeks before presentation. The birdwas not being monitored and wasfound hanging upside down from a treelimb with the transmitter entanglingthe legs. Radiographs indicated ne-crosis of both femoral heads. EMGsindicated denervation of both pelviclimbs. The bird was euthanatized.
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nal effusion or organomegaly, ultrasound may beused to characterize lesions (Figure 12.66).14,19,20
Most studies can be performed without anesthesia.Patients may be held or secured with a plexiglassrestraining device. Many birds that are minimallyrestrained in an upright position are extremely toler-ant of the procedure. Feathers may be parted orremoved, and a water-soluble, acoustic coupling gelis used to improve the transducer contact with theskin.
A 7.5 MHz end-fire mechanical sector scanner orphased array scanner is best in most birds, but 5.0MHz and 10 MHz transducers may also be used.Higher frequency scanners provide less tissue pene-tration but finer resolution and are most useful insmaller species. Linear array transducers can also beused, but because of their shape, they do not conformwell to the patient’s body.
If the patient is in dorsal recumbency, the transduceris placed just caudal to the sternum and the beam isangled cranially. The liver has a uniform, slightlygranular, echogenic pattern and is easily recognized(Figure 12.61). The right and left hepatic veins canbe identified as anechoic channels on the dorsome-dial aspect of the liver. A uniform, hyperechoic, he-patic parenchyma has been described in birds withfatty liver degeneration and hepatic lymphoma.16
Discrete hyperechoic masses throughout the livermay represent granulomas, abscesses or neoplasms.
Hepatomegaly should be suspected if the liver can bedetected caudal to the sternum. Ultrasound is oflittle value in detecting acute or chronic hepatitis,and it is difficult to differentiate between cirrhosisand necrosis. Granulomas and neoplasms typicallyappear as focal hyperechoic walls with an echoiccenter. Hematomas and subcapsular bleeding willappear hypoechoic.
The liver may be used as a window to visualize thecardiac silhouette. Pericardial effusion and enlarge-ment of cardiac chambers and valvular abnormali-ties can be detected in larger species. Pulmonarymasses such as large granulomas have been definedusing ultrasonography. A lateral approach can beused for visualization of the spleen, which is nor-mally hyperechoic in comparison to the liver and isdifficult to define unless enlarged.16
Ultrasonographic visualization of the kidneys andgonads is not possible due to the presence of the air
sacs, although large ovarian follicles can occasionallybe defined. Ultrasound can be used to differentiatebetween soft-shelled eggs and egg-related peritonitis.Poorly mineralized eggs are often oval with a hyper-echoic rim surrounding a hypoechoic content. Withegg-related peritonitis, there is a heterogeneous hy-perechoic appearance to the coelomic cavity (Figure12.66). Effusion due to other processes is often an-echoic or hypoechoic.
The presence of ingesta or gas will obscure portionsof the gastrointestinal tract. Differentiation of theproventriculus, ventriculus and cloaca can be en-hanced by administering water.
Ultrasound-guided biopsy can be used to collect diag-nostic samples from the liver. The patient must besedated or anesthetized. A variety of needles may beused for the biopsy. In larger species a 22 ga Westcottneedle is used to obtain specimens for cytology, his-tology and culture. Spinal needles and 25 ga hypoder-mic needles may be used, but may be difficult tolocalize with the ultrasound beam and often yieldonly enough material for cytology.
Nuclear Scintigraphy
The potential value of nuclear medicine studies inavian patients remains unexplored. The usefulnessof musculoskeletal scintigraphy in other species iswell recognized.9 Three-phase bone scans allowevaluation of the blood supply, soft tissue componentand skeleton and are especially useful in occult le-sions or abnormalities that are undetectable on sur-vey radiographs. Unexplained abnormalities of theextremities, especially following trauma, would bemost suitable for bone scintigraphy. Evaluation of theextent of osteomyelitis, joint disease, vascular com-promise, impaired fracture healing and less com-monly, bone neoplasia, is enhanced by nuclear medi-cine studies.
Technetium-99m(99mTc) is the isotope most frequentlyused because of its short half-life (six hours) and idealenergy range (140KeV). For bone scanning, the ra-diopharmaceutical most commonly used is 99mTcmethylene diphosphonate (MDP). A whole body scanof most birds is easily obtained because the entirepatient can rest on the head of the gamma camera.
Patients must be kept motionless, so sedation oranesthesia is necessary. One millicurie of radioiso-tope is administered intravenously, and dynamic im-ages are obtained immediately for the vascular
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CHAPTER 12 IMAGING TECHNIQUES
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phase, and within the first 15 minutes for the softtissue phase. Delayed static images are taken withinthree to four hours for the bone phase.
Computed Tomography
Computed tomography (CT) is superior to other mo-dalities except magnetic resonance imaging forevaluation of head trauma and abnormalities involv-ing the brain and spinal cord; however, the lack ofavailability and high cost often prevent the use of
computed tomography in birds. Patients must beanesthetized to prevent any motion during the scan.Technical factors are inadequately studied in birds;however, slice section thickness ranging from 2 mmto 5 mm non-overlapping with varying window set-tings have been described for body scans.8,17 Thevalue of CT in avian diagnostic radiology remainsrelatively uninvestigated, but characterization of le-sions with CT should prove as valuable as in otherspecies.
References and Suggested Reading
1.Blackmore DK, Cooper JE: Diseases ofthe reproductive system. In PetrakML (ed): Diseases of Cage and AviaryBirds 2nd ed. Philadelphia, Lea andFebiger, 1982, pp 458-467.
2.Bush M, et al: The healing of avianfractures: A histologic xeroradiog-raphic study. J Am Anim Hosp Assoc12(6):768-773, 1976.
3.Curry TS, et al: Christensen’s Physicsof Diagnostic Radiology. Philadel-phia, Lea and Febiger, 1990.
4.Evans S: Avian Radiography. InThrall DE (ed): Textbook of Veteri-nary Diagnostic Radiology. Philadel-phia, WB Saunders, Co, 1986.
5.Hendee WR, et al: Radiologic Physics,Equipment and Quality Control. Chi-cago, Mosby Yearbook Medical Pub-lishers Inc, 1977.
6.Krautwald ME: Radiographic exami-nation of the urinary tract in birdswith organic iodinated contrast me-dia. Proc Assoc Avian Vet, 1987, pp177-193.
7.Krautwald ME, et al: Atlas of Radio-graphic Anatomy and Diagnosis ofCage Birds. Berlin, Paul Parey, 1992.
8.Krautwald ME: Radiology of the respi-ratory tract and use of computed to-mography in psittacines. Proc AssocAvian Vet, 1992, pp 366-373.
9.Lamb CR: Bone scintigraphy in smallanimals. J Am Vet Med Assoc191(12):1616-1621, 1987.
10.McMillan MC: Avian radiology. In Pe-trak, ML (ed): Diseases of Cage andAviary Birds 2nd ed. Philadelphia,Lea and Febiger, 1982, pp 329-360.
