Diseases of the Pleura

Question 1

What is a pleural effusion?

When can it be detected on CXR? And clinically?

Answer 1

• Pleural effusion is an excessive accumulation of fluid in the pleural space.
• It can be detected on X-Ray when ≥300mL of fluid is present, and clinically, when ≥500mL is present.

Question 2

Describe the appearance of a pleural effusion on CXR.

Answer 2

• The CXR appearances range from obliteration of the costophrenic angle to dense homologous shadows occupying part or all of the hemithorax.
• Fluid below the lung (a subpulmonary effusion) can stimulate a raised hemidiaphragm.
• Fluid in the fissures may resemble an intrapulmonary mass.

Question 3

Define transudate.

Answer 3

• Effusions that are transudates can be bilateral but are often larger on the right.
• The protein content is <30g/L, the lactate dehydrogenase (LDH) is <200IU/L and the fluid to serum ratio is <0.6.
• Transudates are watery.

Question 4

What are the causes of transudates?

Answer 4

• Heart failure
• Hypoproteinaemia (e.g. nephrotic syndrome)
• Constrictive pericarditis
• Hypothyroidism
• Ovarian tumours producing right-sided pleural effusion – Meigs syndrome

Question 5

Define exudate.

Answer 5

• The protein content of exudates is >30g/L and the LDH is >200IU/L.

Question 6

What are the causes of exudates?

Answer 6

• Bacterial pneumonia
• Carcinoma of the bronchus and pulmonary infarction – fluid may be blood-stained
• TB
• Autoimmune rheumatic diseases
• Post-MI syndrome
• Acute pancreatitis
• Mesothelioma
• Sarcoidosis
• Yellow-nail syndrome (effusion due to lymphoedema)
• Familial Mediterranean fever
• Exudates are thick and pusy.

Question 7

What is Light’s criteria?

Answer 7

• Criteria to distinguish between exudative effusion and transudative effusion.

Question 8

Describe the diagnosis of pleural effusion.

Answer 8

• Diagnosis is by pleural aspiration, usually done with ultrasound guidance.
• This is necessary for all but very small effusions.
• A needle is inserted under local anaesthetic through an intercostal space towards the top of the area identified on USS.
• Fluid is withdrawn and the presence of any blood is noted.
• Samples are sent for cytology, protein estimation, LDH and bacteriological examination, including culture and Ziehl-Neelsen / auramine staining for TB.
• Large amounts of fluid can be aspirated through a large-bore needle to help relieve extreme breathlessness.

Question 9

What is a pneumothorax?

What are the 2 types?

Answer 9

• Pneumothorax is air in the pleural space.
• Either spontaneous or post-trauma to the chest.
  
  • Spontaneous pneumothorax most common in young males (male:female 6:1); often they are tall and thin.

Question 10

What is the cause of spontaneous pneumothorax?

Answer 10

• Spontaneous pneumothorax is caused by the rupture of a pleural bleb, usually apical, and is thought to be due to congenital defects in the connective tissue of the alveolar walls.
• In patients >40, the usual cause is COPD.
• Rarer causes include bronchial asthma, carcinoma, breakdown of a lung abscess leading to bronchopleural fistula, and severe pulmonary fibrosis with cyst formation.

Question 11

What causes a pneumothorax to be localised or generalised?

Answer 11

• Pneumothorax may be localised if the visceral pleura has previously become adherent to the parietal pleura, or generalised if there are no pleural adhesions.

Question 12

How does a bronchopleural fistula develop?

Answer 12

• Normally, the pressure in the pleural space is negative but this is lost once a communication is made with atmospheric pressure; the elastic recoil pressure of the lung then causes it to deflate partially.
• If the communication between the airways and the pleural space remains open, a bronchopleural fistula results.

Question 13

How long does it take for a pneumothorax to resolve?

Answer 13

• Once the communication between the lung and the pleural space is closed, air will be reabsorbed at a rate of 1.25% of the total radiographic volume of the hemithorax per day.
• Thus, a 50% collapse of the lung will take ~40 days to reabsorb completely once the air leak is closed.

Question 14

What is a tension pneumothorax?

Answer 14

• It has been postulated that a valvular mechanism may develop through which are can be sucked into the pleural space during inspiration but not expelled during expiration.
• The intrapleural pressure remains positive throughout breathing, the lung deflates further, the mediastinum shifts, and venous return to the heart decreases, with increasing respiratory and cardiac embarrassment.
• This is tension pneumothorax, and is very rare, except in patients on positive pressure ventilation.

Question 15

Outline the presentation and evaluation of suspected pneumothorax.

Answer 15

• The usual presenting features are sudden onset of unilateral pleuritic pain or progressively increasing breathlessness.
• If the pneumothorax enlarges, the patient becomes more breathless and may develop pallor and tachycardia.
• There may be few physical signs if the pneumothorax is small.
• Evaluated using CXR.

Question 16

Outline the treatment options for pneumothorax.

Answer 16