RADIOLOGY OF PLEURA

PLEURA

• Pleura is a serous membrane of mesodermal origin that envelops the lungs,mediastinum ,diaphragm and rib cage.

• Composed of mesothelial layer and underlying connective tissues.

• Similar to any other serous sac in the body ,pleura consists of parietal and a visceral layer.

PLEURA

• The lung is covered with visceral pleura and the adjacent surfaces of the mediastinum, chest wall, and diaphragm are lined by parietal pleura. These layers are in continuity both at the hilum and below ----- pulmonary ligament

• The visceral and parietal pleura are separated by a potential space that normally contains only a few ml of fluid (up to 15 ml)

• Radiologically, the normal pleura is a hairline of soft-tissue density - only seen when it is parallel to the X-ray beam

• On high-resolution computed tomography (HRCT) the pleura may be identified when it forms a fissure. Depending on its obliquity to the imaging plane, a fissure generates a thin, high-density line or band.

• With conventional CT images (10 mm collimation) a fissure cannot usually be resolved as such, though its position is often indicated by an avascular band.

• Peripherally on CT and HRCT there is a thin line separating the lung margin and the fat lying inside the internal intercostal muscle

• This line (the lung–chest wall interface) connects the inner aspects of the ribs and is 1–2 mm thick.

• Despite its thinness this line has a complex structure consisting of:

– two layers of pleura

– subparietal pleural fat (inconstant)

– endothoracic fascia

– the innermost intercostal muscle.

Pleural thickening is most reliably assessed on the inside of the ribs (large arrow).

(B) identify smaller plaques (arrows) and allows the better differentiation of structures such as intercostal veins (arrowheads) that

can mimic plaques.

Imaging modalities

• CXR

• CT

• USG

• MRI

PLEURAL PATHOLOGY

• Grossly, pleural disease is manifested by the accumulation of fluid or air in the pleural space, by pleural thickening, or by the presence of a pleural mass.

Pleural effusion

• Commonest abnormality of pleura • Disruption of any part of pleural fluid dynamics (i.e hydrostatic

pressure ,colloid osmotic pressure ,capillary permeability or lymphatic drainage)can result in the formation of an abnormal fluid collection.

• Associated with all the major pathological processes eg.traumatic ,inflammatory ,CVS,autoimmune,metabolic and neoplastic.

• A number of different types of fluid may accumulate in the pleural space, the commonest being transudate, exudate, blood and chyle

• All types of pleural effusion are radiographically identical, though historical, clinical, and other radiological features may help limit the diagnostic possibilities.

• Sometimes CT and MRI can also help in specifying the diagnosis.

General Specific

Hypoproteinaemia Hepatic cirrhosis, nephrotic syndrome, other hypo-proteinaemic states

Cardiovascular disease Constrictive pericarditis, superior vena caval obstruction, post-cardiac injury syndrome, pulmonary thromboembolism

Neoplasm Bronchial carcinoma

Metastases (lung/pleura)

Pleural tumour (benign, malignant)

Lymphoma

Infection Bacterial (including, tuberculosis), viral, chlamydial, protozoal, metazoal, and fungal

Trauma Ruptured oesophagus

Post-surgical (thoracic/abdominal)

Open/closed chest trauma

CVP line insertion, ventriculopleural shunt

Radiation

Inhalation Asbestos exposure

Inflammatory (non-infectious)

Rheumatoid disease, SLE, Wegener’s granulomatosis

Drug toxicity Methotrexate and other drugs

Subdiaphragmatic disease Ascites-related (transudate, malignant, Meigs’ syndrome, peritoneal dialysis)

Pancreatitis (acute, chronic)

Subphrenic and hepatic abscess

Uraemic pleurisy

Splenic infarction

• Bilateral pleural effusions tend to be transudates because they develop secondary to generalized changes that affect both pleural cavities equally—a rise in capillary pressure or a fall in oncotic pressure of the blood.

• Some bilateral effusions are exudates - metastatic disease, lymphoma, pulmonary embolism, rheumatoid disease, systemic lupus erythematosus (SLE), post-cardiac injury syndrome, myxoedema, and some ascites-related effusions.

• Right-sided effusions are typically associated with ascites, heart failure and liver abscess, and left effusions with pancreatitis, pericarditis, oesophageal rupture and aortic dissection.

• Massive effusions are most commonly due to malignant disease, particularly metastases (lung or breast), but may also occur in heart failure, cirrhosis, tuberculosis, empyema, and trauma.

The goals of diagnostic imaging are threefold

1. detection of the effusion and differentiation from other pathological pleural processes

2. detection of underlying pulmonary, cardiac, mediastinal or abdominal pathology

3. when possible, trying to make a specific diagnosis.

• The radiological signs of a pleural effusion depend on the posture of the patient and the distribution of the fluid, which may be free (typical or atypical configuration) or loculated.

Imaging pleural effusion

Chest-film• Free pleural fluid

A small amount of free fluid may be undetectable on an erect PA chest radiograph as it tends initially to collect under the lower lobes

Such small subpulmonary effusions can be demonstrated by US or CT.

An alternative technique, the lateral decubitus chest radiograph, has largely been replaced by these newer techniques

Selective accumulation of a pleural effusion beneath a lower lobe. It is common for a pleural effusion to collect initially underneath a lower lobe. The sharp anterior margin is delineated by the oblique fissure.

Sub-pulmonary pleural effusion. (A) On the erect PA film the effusion simulates a high hemidiaphragm. (B) A right lateral decubitus view

demonstrates the fluid

• As the amount of effusion increases, the posterior and then the lateral costophrenic angles become blunted, by which time a 200–500 ml effusion is present.

• Following this the classical signs develop, viz. homogeneous opacification of the lower chest with obliteration of the costophrenic angle and the hemidiaphragm.

• The upper margin of the opacity is concave to the lung and is higher laterally than medially.

• Above and medial to the meniscus there is a hazy increase in opacity owing to the presence of fluid behind and in front of the lungs.

• Fluid intrusion into fissures will add complicating opacities to the classical appearance described above.

• These commonly take the form of a ‘middle lobe step’, or a broad band with a curvilinear inner margin extending from mid-lung to the chest wall, often becoming denser as it passes laterally.

Right pleural effusion and left hydropneumothorax effusion obscures the hemidiaphragm and the right costophrenic angle. The

meniscus on the right has a second, faint medial component caused by intrusion of fluid into the oblique fissure.

• Massive effusions cause dense opacification of the hemithorax with contralateral mediastinal shift.

• Absence of mediastinal shift with a large effusion raises the strong possibility of obstructive collapse of the ipsilateral lung.

• Large effusions sometimes cause diaphragmatic inversion, particularly on the left where the diaphragm lacks the support of the liver.

• This can be detected on either side by US, and on the left by plain radiographs using the gastric and colonic gas shadows to localize the hemidiaphragm.

• There are a number of causes other than a massive pleural effusion for an opaque hemithorax, which is frequently produced by a combination of lesions. In such a situation both US and CT can be used with advantage to identify the various components

Massive pleural effusion without mediastinal shift. Despite a massive effusion the trachea (arrows) and mediastinum remain central.

This is seen with obstructive collapse of the ipsilateral lung or diffuse pleural malignancy—in this case obstructive collapse.

• Although pleural fluid collects initially under the lung, it is unusual for it to remain localized in this site once its volume exceeds 200–300 ml. This does happen occasionally, however, and may be suspected from an erect PA and lateral radiograph.

• On a PA radiograph this subpulmonary effusion presents as a ‘high hemidiaphragm’ with an unusual contour that peaks more laterally than usual, has a straight medial segment, and falls away rapidly to the costophrenic angle laterally, which may or may not be blunted

• The apparent hemidiaphragm also appears unduly opaque and fewer vessels are seen through it than normally. On the lateral view the anterior edge often corresponds to the major fissure and is thus straight, with a tail of fluid sometimes passing up into the fissure itself. The posterior costophrenic angle may be blunted.

• With left-sided subpulmonary effusions, there is increased separation between the stomach gas and the apparent hemidiaphragm. Unless a subpulmonary effusion is loculated, which is unusual, a lateral decubitus radiograph will confirm the diagnosis, as will US or CT.

• Sometimes fluid accumulates between the lung and visceral pleura, a common finding in heart failure.

• This lamellar effusion gives a vertical band shadow of soft-tissue density between the lung and the chest wall above the costophrenic angle. This fluid collection remains fixed with postural change, and it is not a true pleural effusion because it lies outside the pleural sac.

• It is a manifestation of a waterlogged lung interstitium and is often accompanied by septal lines.

• There are many other atypical patterns of pleural effusion. Common ones include triangular retrocardiac effusions simulating left lower-lobe collapse, or effusions that are higher medially than laterally. These patterns may be related to the presence of the pulmonary ligament.

Lamellar effusion. A lamellar effusion is characterized by a soft-tissue density, approximately parallel to the chest wall immediately above the

costophrenic angle. It is caused by fluid accumulation beneath the visceral pleura and is commonly seen in heart failure.

Causes of opacification of a hemithorax

Pleural effusion

Consolidation

Collapse

Massive tumour

Fibrothorax

Combination of above lesions

Pneumonectomy

Lung agenesis

Loculated (encysted, encapsulated) pleural fluid

• Fluid can loculate between visceral pleural layers in fissures or between visceral and parietal layers, usually against the chest wall.

• It is unusual for this to happen without some additional radiographic clue as to the presence of pleural disease.

• Both US and CT can be used to distinguish loculated fluid from solid lesions.

• Fissural interlobular loculation is seen particularly in heart failure and may produce the so-called phantom tumour

• which can recur in the same place on repeated occasions.

• Viewed in lateral view it is sharply marginated and biconvex and has a tail passing along the fissure.

• The en face appearances depend on the thickness of the effusion. If it is relatively thin, it may just produce a vague area of increased radio-opacity.

• If thick, however, it may appear clear-edged and mass-like.

• A common problem in practice is the differentiation of encysted fluid in the lower right oblique fissure from a middle lobe collapse.

• Observations that favour a collapsed and consolidated middle lobe rather than an effusion include non-homogeneity, a straight or concave border in the lateral view, a wedge-like outline with the base reaching the sternum, and absence of the minor fissure.

• Fluid can also loculate against the chest wall.

• Viewed tangentially, this variety of effusion appears as a localized homogeneous opacity, convex to the lung and sharp-edged, with a rather low profile that tails off against the chest wall.

• En face it has features typical of a localized pleural

shadow, with one edge sharp and the other fading off.

• Sometimes there is an extension into an adjacent fissure. In case of doubt, a CT scan can be performed.

Encapsulated fluid on PA (A) and lateral (B) chest radiographs. Pleural fluid is encapsulated in the major fissure (arrows) and against the anterior chest wall. These encysted fluid collections can mimic a

lung tumour (‘Phantom tumour’).

Pleural fluid encysted against the chest wall. PA chest radiograph (A) and enhanced CT (B). In case of doubt, CT can be helpful to differentiate a real lung tumour from encapsulated pleural fluid

(Phantom tumour). CT shows a low-density opacity adjacent to the chest wall.

Pleural effusion in the supine patient

• In the supine patient, pleural fluid layers out posteriorly and the meniscus effect, is not appreciated.

• The main radiographic finding is a hazy opacity like a veil affecting the whole or the lower part of the hemithorax, with preserved vascular opacities in the overlying lung.

• Additional signs include haziness of the diaphragmatic margin, blunting of the costophrenic angle, a pleural cap to the lung apex, thickening of the minor fissure, and widening of the paraspinal interface.

Pleural effusion in a supine patient. In this supine patient a right-sided effusion produces a veil-like opacity in the lower chest through which preserved lung vessels can be seen. In addition the diaphragm

is ill-defined, the costophrenic angle blunted and there is an apical cap.

Ultrasound

• Pleural fluid, especially when it is a transudate, is commonly echo-free and marginated on its deep aspect by a highly echogenic line at the fluid–lung interface.

• Exudative and haemorrhagic effusions may be echogenic and are often accompanied by pleural thickening. The pattern of echoes may be homogeneous, complex, or septated.

• Features that help distinguish a fluid from a solid echogenic lesion include changes in shape with breathing, the presence of septa

• It can be used to distinguish between pleural fluid, solid pleural lesions and peripheral lung lesions.

• In peripheral lung lesions, the presence of fluid bronchograms and vessels on Doppler examination will positively identify consolidation.

• In addition, pleural lesions characteristically make an obtuse angle with the chest wall, whereas with intrapulmonary lesions the angle is often acute.

• This ability of US to distinguish pulmonary lesions (collapse, consolidation, abscess) from pleural effusion is particularly useful when it comes to the evaluation of the opaque hemithorax, in which situation US is the initial examination of choice

• US has a number of important roles in the evaluation and management of pleural fluid.

• US can also be used to identify small amounts of pleural fluid, or pleural fluid in unusual locations, as with a subpulmonary effusion.

• US is widely used to localize pleural fluid for aspiration and identify any solid components to allow guided biopsy.

• Furthermore, US may identify the cause of an effusion when it lies inside or even outside the chest (e.g. a. subphrenic abscess, metastasis)

Ultrasound of an empyema. The pleural fluid is separated by septa (arrows). Although the pleural fluid is echo-free in part, some areas return echoes owing to the turbid nature

of the empyema fluid.

Opaque hemithorax—US. There is a small amount of poorly echogenic pleural effusion (E) surrounding a massively consolidated

lung (C) that contains air bronchograms (arrows).

Ultrasound examination of a pleural effusion caused by a pleural metastasis. The US demonstrates a pleural effusion (E) and soft-

tissue pleural masses (arrows); (L) = collapsed lung

Computed tomography

• CT provides information similar to that obtained by US. It is very sensitive in detecting pleural fluid and can distinguish between free and loculated fluid

• Accurate localization of such loculated effusions is useful prior to drainage.

• CT distinguishes between parenchymal lung disease and pleural disease, a distinction that it is often facilitated by a bolus of intravenous (IV) contrast medium.

• CT can characterize the morphology of the pleural thickening that often accompanies a pleural effusion, distinguishing between malignant thickening (nodular, with focal masses) and benign thickening, which is typically uniform

• CT can also identify any underlying lung disease that might have provoked an effusion and it facilitates percutaneous aspiration and biopsy.

• A pleural effusion appears on CT as a dependent, sickle-shaped opacity with a lower CT number than that of any adjacent pleural thickening or mass.

• CT numbers do not allow a distinction between transudate and exudate, but parietal pleural thickening on contrast-enhanced CT almost always indicates the presence of a pleural exudate.

• The higher density of clotted blood in a haemothorax is sometimes apparent.

• The fat-containing chylothorax does not have a lower CT number than normal, because of its protein content.

• Loculated effusions have a lenticular configuration with smooth margins and displace the adjacent parenchyma.

Pleural fluid encysted against the chest wall. PA chest radiograph (A) and enhanced CT (B). In case of doubt, CT can be helpful to differentiate a real lung tumour from encapsulated pleural fluid

(Phantom tumour). CT shows a low-density opacity adjacent to the chest wall.

Massive pleural effusion, CT. CT shows the important pleural effusion together with the enhanced atelectatic left lung. Notice also the

homogeneous and regular thickening of the parietal pleura (arrows) caused by inflammation.

CT of benign pleural disease. On the right there is a sterile parapneumonic effusion, whereas on the left there is an empyema

containing air following thoracocentesis. Contrast medium has enhanced the inflamed, thickened pleura on the left which, unlike the

usual appearance in a malignant pleura, is smooth.

Signs that help in distinguishing between basal pleural fluid and ascites:

• The displaced crus sign. Pleural fluid displaces the diaphragmatic crus away from the adjacent vertebral body, whereas ascites has the reverse effect.

• The diaphragm sign. Fluid within the confines of the diaphragm is ascitic and fluid outside is pleural.

• The bare area sign. Ascitic fluid doesn’t accumulate over the bare area on the posteromedial surface of the right lobe of the liver.

• The interface sign The interface between liver or spleen and a pleural effusion, as assessed away from the dome of the diaphragm, is hazy

The ‘displaced crus’ sign. Pleural fluid displaces the left crus (arrow) away from the vertebra (ascitic fluid causes the opposite

displacement).

The ‘bare area’ and ‘interface’ signs. Pleural fluid characteristically has an ill-defined interface with the liver (curved arrow) and surrounds the liver completely on its posterior aspect (‘bare area’ sign). A linear

opacity (arrows) mimics the diaphragm but is caused by collapsed lung, as proved by contiguous sections.

Magnetic resonance imaging

• MRI has a limited role in the evaluation of pleural effusion. Pleural fluid has a low signal on T1-weighted sequences and a high signal on T2-weighted images, with a tendency for exudates to give a higher signal than transudates on T2-weighted sequences.

• In addition, complex exudates have greater signal intensity than simple exudates. It may also be possible to differentiate transudates from exudates using a triple echo pulse sequence and benign from malignant changes using high-resolution MRI.

• A chylous effusion can cause a high signal intensity on T1-weighted images similar to subcutaneous fat. In the subacute and chronic stage haematomas show a bright signal intensity on T1-weighted images, surrounded by a dark rim caused by haemosiderin.

Empyema

• Empyema is a suppurative exudate, which is usually parapneumonic.

1. Exudative stage: assoc.with pneumonic process adjacent to visceral layer

2. Fibropurulent stage:occurs later d/t bacterial invasion of pl.fluid

3. Organization stage: Fibroblasts grow and form inelastic membrane called pleural peel encase the lung with thick exudates.The fluid may drain spontaneously through chest wall (empyema neccesitans) or into the lung producing bronchopleural fistula.

• Appearance on CXR –similar to pl.effusion.• Fibropurulent fluid collctn have a strong

tendency to loculate and fluid is usually fixed in position.(d/d Lung abscess)

• Malignant neoplasms may arise in the wall of chronic empyema cavities mostly in tubercular.

• NHL,SCC,mesothelioma ,and sarcoma may occur.

• Diff. to Dx neoplasm in chr.empyema.• MRI—difference in signal intensity b/w mature

fibrous tissue and neoplastic tissue.

Plain radiographic and CT features of empyema and lung abscess

  Empyema Lung abscess

Shape of space Usually lenticular Essentially spherical

Length of air-fluid levels in different projections

Unequal Approximately equal

Relation to chest wall Contiguous in at least one projection

Often separated on all aspects

Obtuse angle Acute angle

Separation of enhanced pleural layers (‘split pleura’ sign)

Often present Absent

Vessels and airways Displaced Contact margin

Wall Thin, uniform, smooth on both aspects

Thick, nonuniform, irregular on both aspects

Surrounding consolidation

May be absent Usually present

Extension into costophrenic angle

Sometimes present Absent

Change in shape of space with posture

Sometimes present Absent

Bronchopleural fistula

• Bronchopleural fistula differs from a pneumothorax in that the communication with the pleural space is via airways rather than distal air spaces.

• It occurs in two main settings, following

partial or complete lung resection and in association with necrotizing infections

• The diagnosis is made radiologically, the main signs being:

1. Mediastinum which has shifted towards the pneumectomy side following surgery shifts back to midline.

2 the presence of increasing air and decreasing fluid in the pneumonectomy space

3. contralateral aspiration pneumonitis.

• If less than the whole lung has been removed, the main radiological sign is the sudden appearance of an air–fluid level within the pleural space.

Causes of bronchopleural fistula

Trauma Penetrating

Iatrogenic (especially post-pneumonectomy, post-lobectomy, post-biopsy)

Infection Necrotizing pneumonia

Empyema

Tuberculosis

Septic embolus

Infected pulmonary infarct

Empyema with bronchopleural fistula. There is a large peripheral

lesion with a thick wall containing both air and fluid.

Empyema with bronchopleural fistula. An enhanced CT shows a lenticular fluid collection against the chest wall. The lesion makes an

obtuse angle with the chest wall (small arrow) and shows a split pleura sign (same arrow). The pleura is thickened but smooth and

enhancing (large arrow). The empyema followed a pneumonia caused by an inhaled foreign body

Post-pneumonectomy empyema. Enhanced CT. This late-onset post-pneumonectomy empyema was treated with an open window

thoracostoma (arrow). The pleura is thickened and enhancing.

Chylothorax

• Milky effusions d/t presence of trigycerides

• Pseudochylothorax: milky effusion but it is the result of cholesterol or lecithin globulin complexes rather than chylomicrons.

• Occurs in pleural disease of many years duration,with chronic encysted effusion,pleural thickening.

Principal causes of chylothorax

Traumatic Post-surgical (cardiac, thoracic, oesophageal)

Penetrating chest injuries

Nonpenetrating chest injuries

Neoplastic Lymphoma

Metastatic carcinoma

Inflammatory Filariasis

Tuberculosis

Developmental anomalies Lymphangioma

Lymphangio(leio)myomatosis

Tuberous sclerosis

Lymphangiectasia

Central venous obstruction  

Idiopathic  

Haemothorax

• On the plain chest radiograph, an acute haemothorax is indistinguishable from other pleural fluid collections.

• Once the blood clots there is a tendency for loculation and occasionally a fibrin body will form.

• Pleural thickening and calcification are recognized sequelae.

• On CT a haemothorax may show areas of hyperdensity, and in the subacute or chronic stage it will appear on MRI as a high signal on T1- and T2-weighted images

• The commonest cause of haemothorax is trauma, but it is seen in a number of other conditions including ruptured aortic aneurysm, pneumothorax, extramedullary haemopoiesis and coagulopathies.

Haemothorax. Enhanced CT shows an area of hyperdensity against the posterior chest wall, corresponding with clotted blood.

Measurement of lung density: 1 = 10 HU, 2 = 80 HU.

PNEUMOTHORAX

• Air in the pleural space is a pneumothorax.

• When air and liquid are present the nomenclature depends on their relative volumes and the type of liquid.

• Small amounts of liquid are disregarded and the condition is still called a pneumothorax; otherwise the prefix hydro-, haemo-, pyo-, or chylo- is added, depending on the nature of the liquid.

• Air may enter the pleural space by crossing any of its four major boundaries—the chest wall, mediastinum, lung, or diaphragm

Causes of adult pneumothorax

Spontaneous, primary  

Spontaneous, secondary  

Airflow obstruction  Asthma

COPD

Cystic fibrosis

Pulmonary infection  Cavitary pneumonia

Tuberculosis

Fungal disease

AIDS

Pneumatocele

Pulmonary infarction   

Neoplasm  Metastatic sarcoma

Diffuse lung disease  Histiocytosis X

Lymphangioleiomyomatosis

Fibrosing alveolitis

Other diffuse fibroses

Hereditable disorders of fibrous  connective tissue Marfan’s syndrome

Endometriosis (catamenial  pneumothorax)  

Traumatic, noniatrogenic Ruptured oesophagus/trachea

Closed chest trauma (± rib fracture

Penetrating chest trauma

Traumatic, iatrogenic Thoractomy/thoracocentesis

Percutaneous biopsy

Tracheostomy

Central venous catheterization

Primary spontaneous pneumothorax

• Iatrogenic causes apart, the commonest type of pneumothorax in the adult is the so-called primary spontaneous pneumothorax (PSP).

• A pneumothorax occurring without an obvious precipitating event is spontaneous, and if the patient has essentially normal lungs it is in addition primary.

• PSP occurs predominantly in young adults (65% are between 20 and 40 years of age) and it is five times commoner in males than females.

• Untreated, at least one-third of patients will have a recurrence, most commonly within a few years and on the ipsilateral side.

• PSP is nearly always caused by the rupture of an apical pleural bleb.

• Bleb formation and rupture is thought to be promoted by the greater transpulmonary pressure gradient found at the lung apices than at the bases.

• This gradient is magnified in subjects with long lungs, probably explaining why pneumothoraces are commoner in tall, thin individuals.

• The majority of patients with PSP present with chest pain and/or dyspnoea.

• Occasionally PSP is asymptomatic.

Tension Pneumothorax

Right primary spontaneous pneumothorax. The right lung has partially collapsed and an area of extreme low density without vascular

markings becomes visible.

Secondary spontaneous pneumothorax

• A large number of conditions predispose to pneumothorax and in a number of these disorders pneumothorax occurs frequently.

• This is particularly true of histiocytosis X which has an overall prevalence of pneumothorax of about 20%, and lymphangioleiomyomatosis, where it is in the order of 40%.

• Although the frequency in chronic obstructive pulmonary disease (COPD) is lower, it is a serious complication of that condition with significant morbidity.

• Pneumothorax is an unusual but recognized complication of lung metastases and for reasons that are not clear, there is a strong association with sarcomas, which made up 89% of cases in one literature review, osteogenic sarcoma being the commonest.

• A variety of other tumours have been reported, many of which were being treated with chemotherapy at the time when the pneumothorax developed

Spontaneous pneumothorax secondary to a lung metastasis. Metastasis (M) of an osteogenic carcinoma complicated by a small

pneumothorax (arrows).

Catamenial pneumothorax

• Is commonly, but not necessarily, a manifestation of endometriosis.

• It is rare, and seen typically in parous women in their fourth decade.

• Pneumothoraces are characteristically recurrent, occurring in close relation to the menses, and are predominantly right-sided (90%) and small.

Diagnosis

• The diagnosis of pneumothorax is made with the chest radiograph, which also detects complications and predisposing conditions and helps in management

• Skin folds cause problems particularly in neonates and in old people.

• Features that help identify artefacts and skin folds include extension of the ‘pneumothorax’ line beyond the margin of the chest cavity, laterally located vessels, and an orientation of a line that is inconsistent with the edge of a slightly collapsed lung.

• In addition, the margin of skin folds tends to be much wider than the normally thin visceral pleural line.

• In indeterminate circumstances a repeat chest radiograph, an expiratory radiograph, or one taken with the patient in the decubitus position may clarify the situation.

• Should doubt still remain, then CT is particularly helpful in distinguishing between bullae and a pneumothorax.

• A small amount of pleural liquid often accompanies a pneumothorax, and this will have a horizontal upper surface, but because the central ray usually lies above this level, the fluid appears as a C-shaped shadow in the costophrenic angle.

• Sometimes the air–fluid level accompanying a pneumothorax is more eye-catching than the visceral pleural line

• In the supine position pleural air rises and collects anteriorly, particularly medially and basally, and may not extend far enough posteriorly to separate lung from the chest wall at the apex or laterally.

Signs that suggest a pneumothorax under these conditions are:

– an ipsilateral transradiancy, either generalized or hypochondrial

– a deep, finger-like costophrenic sulcus laterally

– a visible anterior costophrenic recess seen as an oblique line or interface in the hypochondrium; when the recess is manifest as an interface it mimics the adjacent diaphragm (‘double diaphragm sign’)

– a transradiant band parallel to the diaphragm and/or mediastinum with undue clarity of the mediastinal border

– visualization of the undersurface of the heart, and of the cardiac fat pads as rounded opacities suggesting masses

– diaphragm depression

Complications

• Haemopneumothorax• This is a common complication of traumatic pneumothorax.

Small amounts of serous or bloody fluid may also occur witha spontaneous pneumothorax but only 2% of individuals develop a clinically significant haemothorax in these circumstances.

• Tension pneumothoraxThis life-threatening complication is present when intrapleural pressure becomes positive relative to atmospheric pressure for a significant part of the respiratory cycle.

• PyopneumothoraxThis unusual complication is seen most commonly following necrotizing pneumonia or oesophageal perforation.

• AdhesionsThese generate straight band shadows extending from the lung margin to the chest wall. They can be identified with CT.

• Re-expansion oedemaThis unusual complication is sometimes seen following the rapid therapeutic re-expansion of a lung that has been markedly collapsed for several days or more. Oedema comes on within hours of drainage, may progress for a day or two and clears within a week. It usually causes only mild morbidity.

Misplaced pleural drain in pneumothorax. A CT in a patient with a right pneumothorax. The pleural drain is misplaced in the lung. A small

haemorrhage surrounds the tip of the catheter.

Tension pneumothorax. In this chest radiograph a left-sided pneumothorax is accompanied by mediastinal shift to the right

and striking depression of the left hemidiaphragm. The right lung is partially collapsed.

PLEURAL THICKENING AND FIBROTHORAX

• Pleural thickening is common and usually represents the organized end-stage of various active processes such as infective and noninfective inflammation (including asbestos exposure and pneumothorax) and haemothorax. When generalized and gross, it is termed a fibrothorax and may cause significant ventilatory impairment.

• Radiologically, pleural thickening gives fixed shadowing of water density, most commonly located in the dependent parts of the pleural cavity.

• Viewed en profile, it appears as a band of soft-tissue density up to approximately 10 mm thick, more or less parallel to the chest wall and with a sharp lung interface.

• En face, it causes ill-defined, veil-like shadowing. Blunting of the costophrenic angle, often with tenting of the diaphragm is a common finding.

• On US, benign pleural thickening produces a homogeneous echogenic layer just inside the chest wall. It is not reliably detected unless it is 1 cm or more thick.

• CT, on the other hand, is very sensitive at detecting pleural thickening, which is most easily assessed on the inside of the ribs, where there should normally be no soft-tissue opacity

• In chronic conditions pleural thickening is commonly accompanied by thickening of the normally inconspicuous fatty layer that lies immediately outside the parietal pleura.

• The contribution made by fat cannot be appreciated as such on the chest radiograph but is easily distinguished on CT by virtue of its low CT number.

• Fibrous pleural thickening is common in the apical pleural cupola. This may be secondary to tuberculosis or represent an apical cap

• Caps are age-related changes of unknown aetiology. Sometimes they have a scalloped contour or are associated with a tenting towards the lung.

• Caps should be distinguished from the companion shadows of the upper ribs, from extrapleural linear fat deposition and most importantly from a Pancoast tumour.

• Companion shadows of the ribs are usually smoothly bordered towards the lung apex, while extrapleural fat is usually bilateral, symmetrical and also located along the lateral chest wall.

• Fibrous pleural thickening can be induced by asbestos exposure.

• This thickening can be diffuse or is more often multifocal. These pleural plaques can undergo hyaline transformation, calcify or ossify. They are most commonly found along the lower thorax and on the diaphragmatic pleura.

• HRCT is superior to chest radiography and conventional CT in the detection of pleural plaques.

• On CT, they appear as circumscribed areas of pleural thickening separated from the underlying rib and extrapleural soft tissues by a thin layer of fat..

• The radiographic definition of diffuse pleural thickening or fibrothorax is somewhat arbitrary.

• It has been suggested that a smooth uninterrupted pleural density that extends over at least a fourth of the chest wall should be considered as being a fibrothorax.

• On CT, fibrothorax has been defined as a pleural thickening that extends more than 8 cm in cranio-caudal direction, 5 cm laterally and with a thickness of more than 3 mm.

• Common causes of fibrothorax are empyema, tuberculosis and haemorrhagic effusion.

• Asbestos exposure-related fibrothorax is less common than pleural plaques and is usually the sequel of a benign exudative effusion.

• CT may be helpful in establishing the aetiology of the fibrothorax. Extensive calcification favours previous tuberculosis or empyema.

• Asbestos exposure-related fibrothorax is usually bilateral and rarely calcified.

• Generalized, postinflammatory pleural thickening must be distinguished from diffuse pleural malignancy caused by mesothelioma, metastatic disease (particularly adenocarcinoma), lymphoma, and leukaemia.

• Mesothelioma and adenocarcinoma cause diffuse pleural thickening which is often lobulated, may surround the whole lung, and may extend into and along fissures.

• These features are frequently obscured by an effusion.

• The most useful signs on CT that indicate malignant as opposed to benign pleural thickening are circumferential thickening, nodularity, parietal thickening of more than 1 cm, and involvement of the mediastinal pleura

• MR signal intensity seems to be a valuable additional feature for differentiating benign from malignant disease. Signal hypointensity with long TR sequences is a reliable predictive sign of benign pleural disease

PLEURAL CALCIFICATION

• Pleural calcification is most commonly seen following asbestos exposure, empyema (usually tuberculous) and haemothorax. In the last two conditions, calcification is irregular, resembles a plaque or sheet, and is contained within thickened pleura.

• En face it is hazy and veil-like but in profile it is dense and linear, paralleling the chest wall. It may occur anywhere but is most common in the lower posterior half of the chest and is usually unilateral.

• This appearance contrasts with that found in silicatosis, particularly of the asbestos-related type, in which calcification occurs as more discrete collections within plaques and is usually bilateral.

• Following tuberculous empyema both the visceral and parietal pleura may be calcified.

PLEURAL TUMOURS

• Localized pleural tumours

• These are relatively uncommon, the commonest being a localized fibrous tumour (localized mesothelioma)

• These lesions most commonly present in middle age, about half the patients being asymptomatic.

• Hypertrophic osteoarthropathy is a well-recognized complication (10–30% of patients) and uncommonly the tumour produces hypoglycaemia.

• Microscopically two-thirds are benign and one-third is malignant.

• The plain radiographic findings are of a pleurally-based, well-demarcated, rounded and often slightly lobulated mass (2–20 cm diameter) .

• Pleural fibromas usually make an obtuse angle with the chest wall and may reach enormous sizes. Occasionally they may arise in a fissure.

• The CT findings are similar to those observed on plain radiography which are those of a large, mobile, mass that is often heterogeneous because of necrosis and haemorrhage, and that frequently enhances after contrast administration and is rarely calcified.

• Malignant types are usually larger than 10 cm and may invade the chest wall.

• Typically these tumours show low signal intensity on both T1- and T2-weighted images.

• Lipomas are asymptomatic benign tumours that are usually discovered incidentally on chest radiographs as sharply defined pleural masses.

• Diagnosis is easy with CT because this examination can delineate the pleural origin and the fatty composition that is homogeneous.

• When heterogeneous on CT and when soft-tissue attenuation components are also found, a liposarcoma should be suspected.

• Pleural lipomas have a high signal intensity on T1-weighted images. On T2-weighted images the signal is moderately bright

• Pleural metastases are the commonest pleural neoplasms.

• They are usually adenocarcinomas with sites of origin including ovary, stomach, breast, and lung.

• Pleural metastatic disease can present as a solitary mass but more often multiple pleural locations are seen. Pleural metastases are very often accompanied by a pleural effusion, which can be the only finding on a chest radiograph.

Diffuse pleural tumours

• Diffuse tumoural thickening of the pleura can be caused by malignant mesothelioma or by pleural metastasis.

• Diffuse malignant mesothelioma is a rare primary neoplasm and its development is strongly related to asbestos exposure.

• It presents on a chest radiograph as an irregular and nodular pleural thickening with or without an associated pleural effusion

• Tumour extension into the interlobar fissures, an accompanying pleural effusion and invasion of the chest wall are best demonstrated on CT.

• On CT, malignant mesothelioma presents as a nodular soft-tissue mass that sometimes shows hypodense areas corresponding to necrosis.

• Metastatic enlargement of the hilar and mediastinal nodes is seen in up to 50% of patients.

• Malignant mesothelioma has a minimally increased signal on T1 and a moderately increased signal on T2.

• Sonography may be a supplementary method for planning biopsy and surgery

Circumferentially thickened rind of nodular pleura with large effusion

mesothelioma staging systems

• The Butchart staging system for malignant pleural mesothelioma is as follows:

• Stage I - Tumor confined to the ipsilateral pleura, lung, or pericardium

• Stage II - Tumor invades the chest wall or mediastinal structures or metastasizes to the thoracic lymph nodes

• Stage III - Tumor penetrates the diaphragm to involve the peritoneum or metastasizes to the extrathoracic lymph nodes

• Stage IV - Distant blood-borne metastases

Stage Location

T1a Ipsilateral parietal pleura only (including mediastinal and diaphragmatic pleura), without visceral pleura involvement

T1bIpsilateral parietal pleura (including mediastinal and diaphragmatic pleura), with scattered foci of visceral pleural

involvement

T2

Ipsilateral pleural surface has at least 1 of the following:

 

Diaphragmatic muscle involvement

Confluent visceral pleural tumor involvement (including fissures)

Extension from visceral pleura into the pulmonary parenchyma

 

T3

Locally advanced but resectable tumor; each ipsilateral pleural surface has at least 1 of the following:

 

Involvement of the endothoracic fascia

Extension into the mediastinal fat

Solitary, completely resectable tumor focus in the chest wall soft tissues

Nontransmural involvement of the pericardium

 

T4

Locally advanced, technically unresectable tumor; each ipsilateral pleural surface has at least 1 of the following:

 

Diffuse extension or multifocal chest wall masses, with or without rib destruction

Direct transdiaphragmatic extension into the peritoneum

Direct extension to the contralateral pleura

Direct extension to 1 or more mediastinal organs

Direct extension into the spine

Extension through to internal surface of the pericardium, with or without pericardial effusion or myocardial involvement

 

NX Regional lymph nodes not assessable

N0 No regional lymph nodes metastases

N1 Metastases in the ipsilateral bronchopulmonary or hilar lymph nodes

N2Metastases in the subcarinal or ipsilateral mediastinal lymph nodes, including the ipsilateral

internal mammary nodes

N3Metastases in the contralateral mediastinal, contralateral internal mammary, and the

ipsilateral or contralateral supraclavicular lymph nodes

MX Distant metastases not assessable

M0 No distant metastases

M1 Distant metastases present

Chest radiograph of a 58-year-old patient with mesothelioma and shortness of breath. This image reveals diffuse, left-sided pleural

thickening, a pleural effusion, and ipsilateral volume loss.

                            

Computed tomography scan of a 58-year-old patient with mesothelioma and shortness of breath (same patient as in Image

3). This image shows the extensive pleural thickening that is characteristic of mesothelioma, effusion, and reduction in the

volume of the affected hemithorax