This chapter covers: Common conditions • Appendicitis • Colonic obstruction • Diverticular disease • Neoplasia: polyp, carcinoma • Sepsis • Colitis • Volvulus Common presentations in which imaging can help • Altered bowel habit: obstruction, carcinoma, diverticular disease • Acute abdominal distension: obstruction • Acute abdominal pain: obstruc- tion, colitis, diverticulitis • Rectal bleeding: carcinoma, di- verticular disease, colitis Look for hepatomegaly or an abdominal mass on clinical examination. Patients should undergo perianal and rectal examination at presenta- tion. This task is often delegated to the house officer. If you are unsure, ask for help from a senior colleague. Imaging strategy Initial imaging in acute presentations usually involves a supine AXR and an erect CXR. CXR may demonstrate free intraperitoneal air beneath the diaphragm (see Chapter 5), and many patients who are acutely ill may have evi- dence of chest sepsis or cardiac failure also. Supine AXR will give information concerning small and large bowel gas pattern, free intraperitoneal air, soft tissues and bony structures. Once initial clinical assessment has been made and a working diagnosis formulated, many patients will require further imaging. Discuss the case with the radiologist to identify the best way (including endoscopy) to reach a diagnosis. US US in colorectal disease can be helpful for initial assessment of: • Possible bowel-related mass • Free fluid or abscess formation • Solid organs. By their nature, many pathologies of the colon are associated with significant bowel gas and when combined with an elderly, immobile or obese patient the use of US may be limited. CT CT can provide significant additional diagnostic information in patients with bowel-related masses and suspected in- flammatory disease or malignancy. CT is increasingly being used as an early inves- tigation in the elderly and frail to avoid rectal contrast studies. Contrast enema This is an essential tool for evaluation of Chapter 6: The lower gastrointestinal tract 81 OWL6 7/6/04 3:13 PM Page 81
Transcript
This chapter covers:Common conditions• Appendicitis• Colonic obstruction• Diverticular disease• Neoplasia: polyp, carcinoma• Sepsis• Colitis• VolvulusCommon presentations in whichimaging can help• Altered bowel habit: obstruction,carcinoma, diverticular disease• Acute abdominal distension: obstruction• Acute abdominal pain: obstruc-tion, colitis, diverticulitis• Rectal bleeding: carcinoma, di-verticular disease, colitisLook for hepatomegaly or an abdominal mass on clinical examination.
Patients should undergo perianaland rectal examination at presenta-tion. This task is often delegated tothe house officer. If you are unsure,ask for help from a senior colleague.
Imaging strategy
Initial imaging in acute presentationsusually involves a supine AXR and anerect CXR. CXR may demonstrate free intraperitoneal air beneath the diaphragm (see Chapter 5), and manypatients who are acutely ill may have evi-dence of chest sepsis or cardiac failure
also. Supine AXR will give informationconcerning small and large bowel gaspattern, free intraperitoneal air, softtissues and bony structures.
Once initial clinical assessment hasbeen made and a working diagnosis formulated, many patients will requirefurther imaging. Discuss the case withthe radiologist to identify the best way (including endoscopy) to reach a diagnosis.
US
US in colorectal disease can be helpfulfor initial assessment of:• Possible bowel-related mass• Free fluid or abscess formation• Solid organs.
By their nature, many pathologies ofthe colon are associated with significantbowel gas and when combined with anelderly, immobile or obese patient theuse of US may be limited.
CT
CT can provide significant additional diagnostic information in patients withbowel-related masses and suspected in-flammatory disease or malignancy. CT isincreasingly being used as an early inves-tigation in the elderly and frail to avoidrectal contrast studies.
Contrast enema
This is an essential tool for evaluation of
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the rectum and colon (combined withendoscopy).
Unprepared contrast enema, usuallyusing water-soluble iodinated contrast,may be used to exclude an obstructinglesion in patients with large bowel ob-struction. Mucosal detail is poor and, ifthe study is negative, follow-up bariumenema or colonoscopy is often needed.
Contrast enema should not be per-formed in patients at risk of perforation(e.g. toxic megacolon). Barium causesperitonitis if it extravasates outside thebowel and should not be used in patientswho may have perforation or where recentdeep biopsies have been performed.Water-soluble contrast should be used.
Maximum diagnostic information isobtained using the double-contrast technique (air and barium) with goodbowel preparation. However, a significantnumber of elderly patients cannot retainair and/or barium and may be immobile.In some of these patients, CT may beused to exclude a gross mass lesion.
MR
MR has a role in staging colorectal car-cinoma, but its use is currently limitedotherwise.
NM
This has a limited role, but it can be usedto assess the extent of inflammatorycolitis.
Appendicitis
This is the most common surgical emergency, with a peak incidence in thesecond and third decades.
The classic signs of appendicitis areabsent in up to one-third of patients and there is a significant rate of clinicalmisdiagnosis.
Imaging may be particularly helpfulin:• The elderly, where symptoms andsigns may be minimal• Children, where history and examina-tion are often difficult• Young women who may have a gynae-cological cause for pain.
Accurate and appropriate imagingreduces the number of normal laparo-tomies and will help to exclude othercauses of appendix-type pain. However,imaging is often not needed followingclinical assessment.
AXR
Look for:• Laminated calcified appendicolith(10–15% of patients)• Evidence of ileus, often localized tothe right iliac fossa• Distortion of psoas margin• Bubbles of air in associated appendixabscess.
US
This represents a non-invasive modalityfor assessment of atypical patients. US is most accurate in children and youngand/or pregnant women, where the appendix is not obscured by gas. US fea-tures of appendicitis include identifica-tion of the appendix as an abnormal,thick-walled and non-compressiblestructure with a distended lumen (Fig.6.1). An appendicolith or associatedabscess formation may also be seen.
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CT
CT is highly accurate in the evaluation ofappendix inflammation and local extent.It is the technique of choice in theelderly, obese or very tender patients orwhere US has been unhelpful and clini-cal concern persists.
Barium studies
Barium studies of small or large bowelmay be helpful in some patients whereinitial US or CT have indicated bowelpathology not clearly related to the appendix.
Colonic obstruction
The major causes of large bowel ob-struction are carcinoma, diverticulardisease and volvulus. Carcinoma, mostcommonly within the sigmoid, accountsfor > 50% of cases. Symptoms are of ab-dominal distension and pain with associ-ated vomiting. A mass may be palpable.
The integrity of the ileocaecal valve isimportant. If it is competent, this pre-vents passage of air into the small bowelif the large bowel is obstructed, leadingto rapid and pronounced colonic andcaecal dilatation, with the risk of is-chaemia and perforation. An incompe-tent ileocaecal valve allows colonicdecompression, with passage of air into
Fig. 6.1 Transverse ultrasound section of the appendix in a patient with appendici-tis. The appendix has a thickened wall (callipers) with a dilated lumen (arrow) anda target appearance.
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the small bowel. Onset of symptoms maythen be more gradual.
AXR
On supine AXR, look for:
• Dilated gas-filled colon proximal tothe site of obstruction (Fig. 6.2)• Paucity of gas in collapsed colon distalto the obstruction• Haustral pattern to differentiate fromsmall bowel
Fig. 6.2 Supine AXR in a patient with large bowel obstruction secondary tosigmoid carcinoma. There is gaseous distension of the large bowel down to the leftpelvis at level of obstruction (arrow).
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• Small bowel dilatation also if ileocae-cal valve incompetent• Evidence of perforation.
If large bowel obstruction is diag-nosed, rectal and sigmoidoscopic exami-nation should be performed to exclude alow obstructing lesion. If negative, thepatient should be considered for contrastenema examination of the large bowel.
CXR
On erect CXR, look for evidence of freeintraperitoneal air, lung metastases andother pathology.
Contrast enema
Although barium is the ideal agent, it cancause problems. It is contraindicated inpatients at risk of perforation and cancause impaction if no obstruction ispresent, as well as interfering with futurecolonoscopy and CT (see Chapter 2). Io-dinated contrast (water-soluble) is oftenused and will exclude gross obstruction(Fig. 6.3).
CT
This can be useful in assessing bowel and adjacent structures, particularly ifpatients are elderly or frail and cannot tolerate a contrast enema.
Pseudo-obstruction
Marked dilatation of the large bowelmay occur in elderly, bedridden patientsor those with neurological or psychiatricdisorders. Gaseous distension often in-volves the rectum also, and faecal loadingmay be present. Sigmoidoscopy andcontrast enema are often needed to
exclude a mechanical obstruction in pa-tients who do not settle with conserva-tive treatment.
Diverticular disease of the colon
This is the most common colonic diseasein the West, with diverticula present inup to 50% of people of 50 years of age,with the sigmoid colon most frequentlyinvolved. Diverticula are out-pouchingsof colonic mucosa and submucosa thatpenetrate between circular muscle fibres.Circular muscle hypertrophy and mus-cular spasm are common. Diverticulardisease is generally diagnosed duringbarium enema examination, often as anincidental finding (Fig. 6.4). Complica-tions of diverticular disease include diverticulitis, fistula formation andhaemorrhage.
Diverticulitis
Diverticulitis is the most common com-plication of diverticular disease, occur-ring in up to 25% of patients. It occurssecondary to mucosal abrasion by faecalmatter within a diverticulum, causinglocal perforation, inflammation andabscess formation. Patients present withleft iliac fossa pain, fever and often an inflammatory mass.
AXR
AXR may demonstrate air within anabscess or secondary ileus. Chronic in-flammation and stricturing with largebowel obstruction is unusual.
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Fig. 6.3 Water-soluble contrast enema film from splenic flexure region shows anobstructing carcinoma. Note ‘apple core’ appearance of stricture with shouldering.
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Barium enema
This is excellent at demonstrating diver-ticular colonic muscular hypertrophyand spasm, and local contrast extravasa-tion into walled-off pericolic abscess. Pa-tients often do not tolerate barium enemaduring an acute episode, and enema doesnot delineate pericolic inflammation.
US
US is often requested as a first-line
investigation for patients with left iliacfossa pain and may demonstrate bowel-wall thickening, a mass or fluid collectionin diverticulitis. However, US is oftennon-diagnostic.
CT
Patients often proceed to CT, which accu-rately delineates diverticula, bowel-wallthickening, pericolic inflammatory changeand abscess formation (Fig. 6.5), and willguide aspiration or drainage of abscess.
Fig. 6.4 Film from double-contrast barium enema series showing florid sigmoid di-verticular disease. Note diverticula and circular muscle hypertrophy. The sigmoidcolon is tortuous and is an area of weakness for barium enema —mucosal lesionscan easily be overlooked. Another problem here is the presence of significant smallbowel reflux of barium, which partially obscures the sigmoid region.
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Fistula formation
A fistula is a communication betweentwo surfaces lined by epithelium. Acolovesical fistula is the commonest type of indiverticular disease and is secondary to recurrent inflammation —these patients present with pneuma-turia. Air in the bladder may be apparenton AXR. The fistula can be demarcatedduring barium enema. CT is very sensi-tive at detecting air in the bladder, with
associated changes in the sigmoid colon. Coloenteric (Fig. 6.6), colovaginaland colocutaneous fistulae may alsooccur.
Remember that fistula formation alsooccurs with malignancy and this shouldbe excluded.
Haemorrhage
This is not related to diverticulitis. It occurs in 30–50% of patients with diverticular disease and may be life-threatening. Haemorrhage is usuallyself-limiting, but re-bleeding is common.
Barium enema or colonoscopy is indi-cated if bleeding is to be investigated as an outpatient. Catastrophic haemor-rhage may require angiography to iden-
Fig. 6.5 Post-contrast CT demonstrates a sigmoid colon diverticular abscess. Thereis an irregular mass containing fluid and air (long arrow). Thick-walled sigmoidcolon abuts the abscess (short arrow).
Note:It is important to remember that perforated carcinoma can mimic diver-ticulitis, and once the acute episodehas settled, patients should undergoendoscopic examination.
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tify the site and to allow potential em-bolization of the bleeding vessel.
Colorectal carcinoma
Colorectal carcinoma is the second mostcommon cause of cancer death. Riskfactors include family history, adenoma-tous polyposis syndromes, chronic ul-cerative colitis and Crohn’s disease. Thevast majority of colorectal carcinomasbegin as benign adenomas, which growover time and undergo malignant trans-formation. Adenomas of > 1 cm are atrisk and > 2 cm malignancy is likely
(50%). Fifty per cent of carcinomas arein the rectum or sigmoid and in range ofthe flexible sigmoidoscope.
Patients with a colorectal carcinomaare at risk of synchronous (carcinomaelsewhere in large bowel) and metachro-nous (colonic carcinoma at a later date)lesions and it is important to evaluate theentire colon at the time of diagnosis.
Polyp detection
Clearly, polyp detection and removalprior to malignant change is essential forprevention of colorectal carcinoma, al-though large-scale population screening
Fig. 6.6 Film from a single-contrast barium enema in the sigmoid region. There isirregular narrowing in the mid-sigmoid region (long arrow) with adjacent divertic-ular disease. Contrast passes via a fistula (short arrow) to communicate with smallbowel. This was secondary to diverticular disease, but exclusion of malignancy is essential.
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is still under investigation. Severalimaging modalities are available; all havestrengths and weaknesses. Colonoscopyis often preferred.
Barium enema
Double-contrast barium enema is highlyaccurate and comparable to colonoscopyin the identification of polyps > 1 cm.This accuracy falls off < 1 cm in size.Completion rate to the caecum is betterwith barium enema. Diagnostic accuracyis impaired:• With poor bowel preparation• If patients cannot retain air or barium• With tortuosity of the bowel, espe-cially in the sigmoid• With extensive associated diverticulardisease• The lower rectum is often not wellseen, particularly if a balloon catheter isused.
Adenomatous polyps may be:• Pedunculated (on a stalk): where risk ofmalignancy is low (Fig. 6.7)• Sessile (flat): villous change and malig-nancy is more likely (Fig. 6.8).
Colonoscopy
Endoscopic assessment of the colonallows identification and also removal ofpolyps. This modality is theoretically theideal, but does have the complications ofsedation and perforation, and technicalfailure is common, for similar reasons, tobarium enema.
CT colonography
This three-dimensional virtual-realityCT technique, following air insufflationof the colon, has shown initial promisingresults.
Fig. 6.7 Decubitus spot film of the hepatic flexure from a double-contrast bariumenema series demonstrates a pedunculated polyp on a stalk (arrows). Note gravi-tational pooling of barium.
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Adenocarcinoma
This may be diagnosed by the threemodalities outlined above — again, colo-noscopy offers the opportunity for histological examination.
CT is useful for identifying primarytumour and is the most reliable methodfor staging:• Luminal mass and bowel wall thicken-ing (Fig. 6.10)• Stranding and nodularity of adjacentfat — may indicate local invasion• Invasion of local structures• Presence of mesenteric disease, as-cites, significant adenopathy• Liver and lung metastases.
Fig. 6.8 Film from double-contrast barium enema demonstrates a large sessilepolyp in the upper rectum (arrow). The surface of the polyp is irregular and, whencombined with the size, malignancy is likely.
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US
Transabdominal US can identify bowel-related masses and will assess the liverparenchyma for metastases.
Transrectal US and MRI accuratelydelineate the layers of the rectal wall andare useful for local staging of disease.Bulky and locally invasive rectal car-cinomas will receive local radiotherapyprior to surgery.
Local complications ofcolorectal carcinoma
• Obstruction: this is common (seeearlier). In patients unfit for immediate
surgery, radiological insertion of an ex-panding metallic stent over a guidewirecan relieve obstruction, giving palliation.Surgery can be considered when thepatient’s condition has improved.• Fistula formation (see earlier)• Perforation: patients may go straightto theatre for surgery.
Follow-up of treated colorectal cancer
Residual large bowel post-resection isfollowed-up regularly, either endoscopi-cally or by barium enema.
CT is the modality currently of choicefor identifying extraluminal local recur-
Fig. 6.9 Film from double-contrast barium enema in a patient with a large trans-verse colon carcinoma (large arrow). There is irregular stricturing of the bowelwith shouldering apparent. Note lung metastases at lung bases (small arrows).
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rence or metastatic disease and is also used to monitor patients withknown metastatic disease undergoingtreatment.
Hepatic metastases may be consideredfor ablation or resection (see Chapter 7).
Abdominal sepsis
Sepsis in the abdomen is a very impor-tant cause of patient mortality, mor-bidity and increased length of hospitalstay. Cases are often complex and greatbenefit may be obtained through directdiscussion with a radiologist.
This section concentrates on in-traperitoneal, subphrenic, psoas andpelvic abscess formation. Diverticular,
pancreatic and hepatic abscesses arecovered elsewhere.
Intraperitoneal abscess
Usually results from secondary infectionof collections of blood, bile or ascites andmay arise in patients who have under-gone bowel or hepatobiliary surgery. Ifpatients have pyrexia or a raised whitecell count only, with no significant ab-dominal symptoms, make sure there isno evidence of chest, urinary or skinsepsis (e.g. infected cannula) prior tofurther investigations.
AXR
AXR may show an ileus or mottled
Fig. 6.10 Post-contrast CT in a patient with caecal carcinoma. There is markedthickening of the caecal wall (arrows).
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gas densities within an intraperitonealabscess and is worth arranging if thereare abdominal symptoms.
US
US is the next investigation of choice for the identification of abdominal andpelvic fluid collections. Bandaging, suturing, pain, obesity and gas oftendegrade US; CT would then be recommended.
Percutaneous drainage under US orCT guidance can be performed in post-operative abscess formation.
Subphrenic abscess
This usually follows bowel surgery orappendicectomy.
AXR
AXR may show mottled gas densities inabscess but air–fluid level and sympa-thetic pleural effusion is best appreci-ated on erect CXR (Fig. 6.11).
US and CT
US or CT will confirm diagnosis ifnecessary.
Fig. 6.11 Erect CXR demonstrates a large right subphrenic abscess post-cholecystectomy. Note air–fluid level (arrows) and right basal pleural effusion.
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Psoas abscess
Psoas abscess often relates to adjacentvertebral, bowel or renal sepsis. Look forevidence clinically of psoas irritationand painful hip flexion.
AXR
AXR may show psoas enlargement andabnormal gas densities. Look carefullyfor renal tract calcification and vertebralbody abnormality (tuberculous ormetastatic bony involvement).
US and CT
US is often limited in evaluation of theretroperitoneum and CT is the idealmodality for psoas assessment andabscess drainage (Fig. 6.12).
Colitis
The three most common forms of colitisare dealt with here: ulcerative, Crohn’sand ischaemic.
Ulcerative colitis
This is a common inflammatory diseaseof the colon and rectum of uncertain aetiology, which initially involves thebowel mucosa but extends to involvedeeper layers. The disease usually commences in the rectum and extendsproximally, with the diagnosis made on sigmoidoscopic biopsy. The terminalileum may be involved (‘backwashileitis’).
Ulcerative colitis runs a variable clinical course — usually with periods of
Fig. 6.12 CT of left psoas abscess secondary to renal calculus disease. A large sep-tated fluid collection involves the left psoas and iliacus muscles (long arrow). Notenormal right psoas muscle (short arrow).
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relapse and remission, although an acuteand fulminant illness may occur. Extra-colonic manifestations are recognised(e.g. arthritis, iritis, rash) in 10%.
AXR
Look for:• Extent of faecal residue — where it is absent this is suggestive of colitic involvement• Bowel wall thickening• Colon diameter (> 6 cm in traversecolon suspicious of toxic megacolon).Colon narrows in chronic disease• Loss of haustration or mural thickening• Evidence of perforation.
Barium enema
This is a useful investigation in ulcera-tive colitis. It is used to assess dis-ease extent, to differentiate ulcerative colitis from other forms of colitis and to detect disease complications (e.g. malignancy).
Barium enema features of ulcerative colitis
Complications of ulcerative colitis
• Toxic megacolon: an acute fulminantillness with colonic dilatation (> 6 cm)and high risk of perforation. It carries ahigh mortality. Toxic megacolon can bediagnosed on AXR (Fig. 6.14). Contrastenema should not be performed becauseof the risk of perforation.• Colonic adenocarcinoma: annual inci-dence of 10% after first decade of thedisease. Carcinomas are often multipleand flat, and scirrhous in nature (Fig.6.13). Patients with ulcerative colitisshould undergo regular colonoscopicscreening with random biopsies to detectdysplasia.
Crohn’s colitis (see Chapter 5)
This is a granulomatous colitis particu-larly involving the right colon, withsparing of rectum and sigmoid colon.However, perianal disease (abscess,fistula, ulceration) is strongly suggestiveof Crohn’s.
AXR
Look for:• Extent of faecal residue, bowel-wallthickening, haustral loss or thickening(Fig. 6.15)• Also look for gallstones, sacroiliitisand avascular necrosis (femoral heads),which are associated with Crohn’s (andulcerative colitis).
Fig. 6.13 Films from double-contrast barium enema in a patient with long-standing ulcerative colitis involving the colon around to the hepatic flexure. Notegranular mucosa with colon lumen narrowed and haustral pattern absent. A complicating carcinoma is seen at the splenic flexure (arrow). Note normal haustral pattern in the right colon.
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Fig. 6.14 AXR in a patient with ulcerative pancolitis and toxic dilatation of thetransverse colon. Note absence of faecal residue and thickening of haustra(arrows). There is a pelvic intrauterine contraceptive device (IUCD).
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Barium enema features of Crohn’s colitis Complications of Crohn’s colitis
• Fistula: enterocolic, enterocutaneous,perianal• Toxic megacolon: less common thanulcerative colitis• Adenocarcinoma: ileum and colon• Abscess formation.
Ischaemic colitis
Patients present with acute abdominalpain and rectal bleeding, and ischaemiccolitis tends to involve the splenic flexureand descending colon at the ‘watershed’area of blood supply between superiorand inferior mesenteric arteries. It ismore common in the elderly with ahistory of cardiovascular disease.
Fig. 6.15 AXR in a patient with Crohn’s colitis. The transverse colon is narrowedand thumb-printing (mucosal oedema) is present (arrows).
EarlyNodular lymphoid hyperplasiaAphthous ulcers‘Cobblestoning’ resulting from longi-
tudinal and transverse ulcers sepa-rated by oedema — ulcers are deep
LateLoss of haustrationStrictures (‘string’ sign)FistulaePseudodiverticula
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AXR
AXR may show segmental muco-sal oedema with thumb-printing. Diag-nosis can be confirmed with bariumenema.
CT
CT demonstrates segmental muralthickening, and also intramural andportal venous gas in severely ill patients(Fig. 6.16).
Caecal volvulus
Caecal volvulus accounts for 3% ofcolonic obstructions and is associatedwith malrotation of the right colon and a
long mesentery allowing the caecum torotate so it lies in the mid-abdomen or,more commonly, the left upper quadrant.
AXR
AXR reveals a dilated gas-filled caecumin the left upper quadrant (Fig. 6.17).The medially placed ileocaecal valve maycause an indentation, giving a kidney or‘coffee-bean’ appearance.
If the ileocaecal valve is incompetent,there will be coexisting small bowel di-latation. The normal caecal gas patternis absent in the right iliac fossa.
A contrast enema is helpful if AXR isatypical, with the tapered end of the obstructed contrast column pointingtoward the torsion.
Fig. 6.16 Post-contrast CT in a severely ill patient with ischaemic colitis. Air is iden-tified peripherally distributed within portal veins in the liver (small arrows). Ascitesis present (large arrows).
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Sigmoid volvulus
This accounts for 1–2% of colonic ob-structions and tends to occur in elderlyor psychiatric patients with large redun-dant sigmoid colons.
Patients present with abdominal painand distension.
AXR
On supine AXR, look for:• Markedly dilated loop of sigmoid
colon extending into the upper abdo-men, converging to the left iliac fossa(Fig. 6.18)• Often dilated large bowel proximally• Absence of gas in the rectum.
A contrast enema may be required insome patients where radiographicalfindings are equivocal. This demon-strates a tapered narrowing of the con-trast column at level of volvulus.
Once the diagnosis has been made, aflatus tube can be passed to decompressthe sigmoid colon to allow patient stabi-lization prior to sigmoid colectomy.
Fig. 6.17 Supine AXR in a patient with caecal volvulus and an incompetent ileo-caecal valve. Note distended air-filled caecum in left upper quadrant (large arrow)and dilated small bowel loops (small arrows).
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Fig. 6.18 Supine AXR in a patient with sigmoid volvulus. Note markedly dilatedsigmoid colon (arrows) with ‘inverted-U’ configuration, converging to the left iliacfossa. Calcified gallstones are seen in the right upper quadrant.
