Pathologies of the Pleura
Pleural effusion
· A collection of serous fluids within the pleural space.
· These can be divided into transudates or exudates using Light’s criteria (1).
· A pleural effusion will develop when the rates of formation and resorption of pleural fluid are unequal.
· Common causes are listed in table 1 (1).
Light's Criteria for Pleural Effusions (1) |
|
Transudate |
Exudate |
Protein
(pleural/serum)
|
<0.5 |
>0.5 |
LDH
(pleural/serum)
|
<0.6 |
>0.6 |
Pleural LDH <2/3 upper limit of normal serum LDH |
Pleural LDH > 2/3 upper limit of normal serum LDH |
Common Causes |
- Hypoalbuminaemia (cirrhosis,
nephrotic syndrome)
- Congestive cardiac failure
- Constrictive pericarditis
|
- Autoimmune diseases
- Oesophageal rupture
- Infection (parapneumonic,
TB,
fungal)
- Pancreatitis
- Post-coronary artery bypass graft surgery
- Pulmonary embolism
|
X-ray:
· Pearl: At least 500mls in size before they are able to be recognized on this imaging.
· On an erect film,
small pleural effusions appear as blunting of the costophrenic angles or costocardiac angles or fluid within the fissures - see figure
· Larger effusions will appear as a homogenous opacity in the hemi-thorax or bilaterally,
with a meniscus shaped superior border - See Fig. 2 .
· If the effusion is large enough,
it can appear as a complete ‘white-out’ of the hemi-thorax,
with mediastinal and tracheal shift.
· Pearl: A ‘white-out’ is also seen following a pneumonectomy.
In this case the trachea will usually shift towards the whiteout due to volume loss from the removed lung.
· If supine,
a pleural effusion may make the hemi-thorax look as if it has been covered in a ‘veil-like’ opacity.
The meniscus is not as noticeable in a supine radiograph.
· Pearl: Although not commonly performed,
a lateral decubitus film will be able to diagnose a smaller amount of fluid,
as low as 5 ml.
see Fig. 3
· Effusions can be loculated,
when the fluid collects between the pleura in different formations,
with small pockets of fluid becoming apparent.
See Fig. 3 .
CT:
CT is useful in detecting pleural effusions,
but is poor at differentiating between transudates and exudates.
It can be used to delineate any pleural pathology as an underlying cause for a concerning pleural effusion - Fig. 4 and Fig. 5 demonstrates a case of a large unilateral pleural effusion further investigated with CT due concern for a malignant cause.
Haemothorax
· Definition: Blood within the pleural space
· Most commonly due to trauma.
· Other potential causes include intrathoracic malignancy,
vascular rupture and pulmonary infarction.
If it occurs in the presence of a pneumothorax also,
it is termed a haemopneumothorax.
X-ray:
· Can be indistinguishable from pleural effusions on plain radiographs.
· Pearl: Look for other signs in trauma e.g.
broken ribs,
widened mediastinum.
CT:
· Measure attenuation of the effusion
· Typical values of a haemothorax would be 35-70 HU.
Simple transudate will be close to 0 HU.
· Blood clots may also be visible.
Pneumothorax
· Definition: Air within the pleural space.
· Causes are spontaneous,
traumatic or post-surgical.
· Further subdivided into primary spontaneous where there is no underlying lung disease,
and secondary spontaneous where there is an underlying lung disease.
X-ray:
· It is usually possible to see the visceral pleural edge sunken down into the hemithorax,
with no visible lung markings beyond this point.
· The space around the lung is radiolucent.
· In the case of a tension pneumothorax,
the mediastinum may be shifted in the opposite direction.
CT :
Pneumothoraces are usually easily diagnosed on CT,
with large radiolucent areas and the lucent edge of the visceral pleural edge being demonstrated.
Tension pneumothorax
This is a life threatening condition,
where the lung is collapsed and there is a large amount of gas in the pleura.
This causes compression of the lung,
increasing the work of breathing and compression of the intrathoracic structures which may lead to cardiorespiratory arrest.
X-ray - see Fig. 6
· Ipsilateral depression of the hemidiaphragm
· Shift of mediastinum to contralateral side
· Ipsilateral increased intercostal spaces
· Treatment of this must be immediate,
and is done by cannulating the 2nd intercostal space and allowing the gas to escape.
Loculated / Encysted pneumothorax - see Fig. 7 and Fig. 8
· Form of pneumothorax where a pocket of pleural air is trapped within a localised area.
· They may occur in a number of situations including in patients with acute respiratory disease treated with mechanical ventilation and post pleural aspiration or drainage in the context of previous pleural inflammation or pleurodesis
· Differential diagnosis :
· lung bulla = air-filled space in the lung parenchyma due to destruction of alveolar tissue,
distal to terminal bronchiole
Pearls: Differentiating pneumothorax vs bulla
· Helpful signs for pneumothorax = visible visceral pleural line
· Expiratory chest radiograph may help delineating a visceral pleural line of pneumothorax
· Presence of other bullae or septations may point towards a bulla.
· "Double wall" sign can be seen in cases with ruptured bulla causing pneumothorax (air outlining both sides of the bulla wall parallel to the chest wall)
Empyema
· A collection of pus within the pleural cavity.
· Commonly associated with pneumonia,
surgery or trauma.
X-ray:
Can resemble pleural effusions on radiographs.
They can also resemble peripheral pulmonary abscesses.
Empyemas tend to form in oval or lens shapes rather than crescents.
They may also have air-fluid levels within.
CT :
Empyemas appear as dense fluid,
sometimes with air.
The pleura can be thickened,
and may even develop into layers,
known as the ‘split-pleura’ sign.
This is useful in differentiating between empyema and lung abscess.
BENIGN PATHOLOGY
Pleural plaques - see Fig. 9
Areas of calcified fibrosis,
most commonly occurring due to asbestos exposure.
They can be unilateral,
bilateral,
multiple or isolated.
They normally arise from the parietal,
mediastinal pleura.
X-ray:
Often,
plaques are seen as increased areas of opacification with the incomplete border sign.
Calcified plaques are often easier to identify.
Often,
a lateral radiograph may be useful as they can be identified as an irregular opacity across these.
CT:
CT is a useful tool to assess pleural plaques,
whether they are calcified or not.
The use of CT allows diaphragmatic domes and lung apices to be interrogated well.
Pleural fibroma - see Fig. 10
· Benign tumours accounting for less than 5% of pleural tumours.
· Mostly originate from the visceral pleura,
and have a tendency to form in the mid to lower zones of the thoracic cavity.
X-ray:
A pleural based mass can be seen on plain radiographs.
They normally have quite clear borders,
but do sometimes present as lobulated.
They can be large in size.
CT:
Pleural fibromas have a soft tissue attenuation.
They tend to have a homogenous appearance,
and can be seen to have good vascularization.
If there are areas that are not as well enhancing,
these could be due to haemorrhage,
necrosis or degeneration.
Pleural lipoma - see Fig. 11
Most common benign,
soft tissue tumour of the pleura.
Originate from the parietal pleura,
and can then extend into the subpleural,
pleural or extrapleural spaces.
Slow growing tumours,
mostly consisting of fatty material.
X-Ray:
Convex shaped mass,
forming an obtuse angle with the pleura.
They are well circumscribed and often slow growing.
They are not associated with underlying rib erosion.
CT:
Homogenous mass with a similar attenuation to fat.
They will not enhance,
and calcifications are rare.
CT also delineates extrapleural lipoma - see figure 12.
Pearl: Use appropriate windowing to find fat density pleural abnormalities.
Pleural Tuberculosis - see Fig. 13
Tuberculous pleural effusions occur in up to 30% of patients with tuberculosis.
It can also cause circumferential pleural thickening.
X-ray:
Appearances can be similar to pleural effusion as described above.
It may also be possible to identify pleural thickening.
CT:
CT is more sensitive in being able to identify thickening of the pleura,
pleural effusions and any associated invasion into the chest wall.
Pleural Sarcoid - see Fig. 14
· Multisystem chronic inflammatory condition of unknown etiology (2)
· Characterized by non-caseous epithelioid cell granuloma formation
· Most common clinical features at presentation are respiratory symptoms (eg,
cough,
dyspnea,
bronchial hyperreactivity),
fatigue,
night sweats,
weight loss,
and erythema nodosum (2)
· Pitfall: 50% of cases of sarcoidosis are asymptomatic (2),
with abnormalities detected incidentally at chest radiography – don’t let history sway your judgement.
· 90% patients with sarcoid present with enlarged mediastinal and hilar paratracheal lymph nodes (2)
X-ray:
· Lymphadenopathy (Stage 1)
· Lymphadenopathy and pulmonary infiltrates (Stage 2)
· Pulmonary infiltrates (Stage 3)
· Fibrosis (Stage 4)
CT:
· Hilar/paratracheal lymphadenopathy
· Micronodules with a Perilymphatic Distribution
· Fibrotic Changes
· Bilateral Perihilar Opacities
Calcified fibrothorax- see Fig. 15
· Fibrosis within pleural space
· Secondary to the inflammatory response by usually the following:
1. tuberculosis / tuberculous pleuritis - usually late sequelae
2. Thoracic empyema
3. Asbestos related pleural disease
4. Rheumatoid arthritis
5. Haemothorax
Radiographic features:
· Calcified pleural thickening
· Mediastinal pleura is usually spared.
· Marked volume loss in the affected hemithorax.
MALIGNANT PATHOLOGY
Mesothelioma - see Fig. 16
· Malignant tumour affecting the mesothelium.
· It is aggressive,
with the majority of these arising from the pleura.
· Mesothelioma has a strong link with asbestos exposure.
· The asbestos fibres cause repetitive irritation which then forms plaques or malignant mesothelioma.
· Latent period usually before the presence of the tumour.
· Histologically,
three types of tumour are described: epithelial (60%),
mixed (25%) and sacromatous (15%) (3)
X-ray:
Pearl: features favouring mesothelioma over benign pleural plaques:
· Volume loss
· Evidence of rib erosion,
malignant pleural effusions or lymph node enlargement.
CT (3):
· Accurate disease staging
· Nodular mass of soft tissue attenuation.
· Runs along pleural surfaces and can invade pleural fissures also.
· Growth typically leads to tumoral encasement of the lung with a rindlike appearance
· Can be seen as pleural thickening,
with or without pleural nodules.
· Concerning if involving mediastinal surface pleural
· A pericardial effusion may indicate transpericardial extension
Pleural metastases- see Fig. 17
· First manifestation usually pleural effusion (4)
· Pitfall: Pleural tumours can present without effusion.
· Over 50% of patients with malignant pleural effusion suffer from dyspnea.
Causes (3):
(1) lung cancer (adenocarcinoma) (40%)
(2) Breast carcinoma (20%) – pleural effusion common
(3) Ovarian cancer
(4) Lymphoma
(5) Gastric carcinoma
(6) Thyroid carcinoma
(7) Invasive thymoma
X-ray:
· Pleurally based masses (4)
· Pleural thickening
· Pleural effusion
· Rib destruction
· Hilar/mediastinal lympadenopathy
CT:
· Pneumothorax
· Hydropneumothorax
· Pneumomediastinum
COMPLEX CASE Broncho-pleural fistula - see figure 18-21
( Fig. 18, Fig. 19, Fig. 20, Fig. 21 )
· Communication between the pleural space and the bronchial tree.
· Post-operative complication of pulmonary resection – most common
· Infection with lung necrosis
· Persistent spontaneous pneumothorax
· Chemotherapy or radiotherapy
· Tuberculosis
· Invasive lung cancer
X-ray:
· Steady increase in intra-pleural airspace – particularly after infection within the lung or pleural space
· New intrapleural air-pleural fluid collection (hydropneumothorax).
The air-fluid level typically extends to the chest wall and shows unequal linear dimensions on orthogonal views conforming to the pleural space
· Post-operatively: Changes in an already present air-fluid level
CT:
· Pneumothorax
· Hydropneumothorax
· Pneumomediastinum
· Underlying lung pathology (potential cause)
· Fistulous communication demonstrated - see Fig. 21 .