Pneumothorax

A pneumothorax refers to the presence of gas in the pleural space. When this collection is constantly enlarging with resulting compression of mediastinal structures it is known as a tension pneumothorax, a life threatening emergency. It is discussed separately.

Epidemiology

Clearly with so many causes of a pneumothorax it is impossible to generalise the epidemiology, however in general primary spontaneous pneumothoraces occur in younger patients (typically less than 35 years of age) whereas secondary spontaneous pneumothoraces occur in older patients (typically over 45 years of age) ⁴.  

Clinical presentation

Presentation is variable and may range from no symptoms to severe dyspnea with tachycardia and hypotension.  If tension, presentation may be with cardiac arrest, distended neck veins and tracheal deviation.

It is interesting to note that some generalisations can be made in regards to the clinical presentation in primary versus secondary spontaneous pneumothoraces. 

• primary spontaneous: pleuritic chest pain usually present, dyspnea mild or moderate
• secondary spontaneous: pleuritic chest pain often absent, dyspnoea usually severe

Pathology

It is useful to divide pneumothoraces into three categories ⁴:

1. primary spontaneous: no underlying lung disease
2. secondary spontaneous: underlying lung disease is present
3. iatrogenic / traumatic

Primary spontaneous

A primary spontaneous pneumothorax is one which occurs in a patient with no known underlying lung disease. 

Secondary spontaneous

When the underlying lung is abnormal, a pneumothorax is referred to as secondary spontaneous. There are many pulmonary diseases which predispose to pneumothorax including:

• cystic lung disease
  • bullae, blebs
  • emphysema, asthma
  • pneumocystis carinii pneumonia (PCP)
  • honeycombing : end stage interstitial lung disease
  • lymphangiomyomatosis (LAM)
  • Langehans cell histiocytosis (LCH)
  • due to apical lung changes from ankylosing spondylitis ¹
• parenchymal necrosis
  • lung abscess, necrotic pneumonia, septic emboli, fungal disease, tuberculosis
  • cavitating neoplasm, metastatic osteogenic sarcoma
  • radiation necrosis
• other
  • catamenial pneumothorax ^2,4 : recurrent spontaneous pneumothorax during menstruation, associated with endometriosis of pleura 

Iatrogenic / traumatic

Iatrogenic / traumatic causes include ^1-4:

• iatrogenic
  • percutaneous biopsy
  • barotrama, ventilator
  • radiofrequency (RF) ablation of lung mass
• trauma
  • pulmonary laceration
  • tracheobroncial rupture
  • acupuncture (some would argue that this is iatrogenic I suppose. It depends on your view of acupuncture)

Radiographic features

Chest radiograph

A pneumothorax is, when looked for, usually relatively easily appreciated. Typically they demonstrate: 

• visible visceral pleural edge see as a very thin, sharp white line
• no lung markings are seen peripheral to this line
• the peripheral space is radiolucent compared to adjacent lung 

• the lung may completely collapse
• the mediastinum should not shift away form the pneumothorax unless a tension pneumothorax is present (discussed separately). 
• subcutaneous emphysema and pneumomediastinum may also be present

In cases where these features are not clearly present a number of techniques can be employed:

• lateral decubitus x-ray:
  • should be done with the suspected side up
  • the lung will then 'fall' away from the chest wall
• expiratory chest x-ray
  • lung becomes smaller and denser
  • pneumothorax remains the same size and is thus more conspicuous : although some authors suggest that there no difference in detection rate ⁶.
• CT scan

When imaged supine detection can be difficult: see pneumothorax in a supine patient, and pneumothorax is one cause of a transradiant hemithorax.

Ultrasound

M-mode can be used to determine movement of lung within the rib-interspace.  Small pneumothoraces are best appreciated anteriorly in the supine position (gas rises) whereas large pneumothoraces are appreciated laterally in the mid-axillary line.

CT

Provided lung windows are examined, a pneumothroax is very easily identified on CT, and should pose essentially no diagnostic difficulty. When bullous disease is present, a loculated pneumothorax may appear similar. 

Treatment and prognosis

Treatment depends on a number of factors :

• size of the pneumothorax
• symptoms
• background lung disease / respiratory reserve

These can be use together to determine the best course of action.  The following guidelines are based on the British Thoracic Society guidelines for the treatment of pneumothorax - local protocol may differ:

• asymptomatic small rim pneumothorax (< 2cm) : no treatment with follow up radiology to confirm resolution
• pneumothorax with mild symptoms (no underlying lung condition) : needle aspiration in the first instance
• pneumothorax in a patient with background chronic lung disease or significant symptoms : intercostal drain insertion (small drain using the seldinger technique)

In patients with recurrent pneumothoraces or who are at very high risk of having recurrent events and have poor respiratory reserve, a pleurodesis can be performed. This can either be medical (e.g. talk poudrage) or surgical (e.g. VATS pleurectomy, pleural abrasion, sclerosing agent)⁴. 

Differential diagnosis

Usually the diagnosis is straight forward, but occasionally other entities should be considered:

• skin-fold: the apparent pleural edge is denser and may be seen extending beyond the chest cavity or seen to fade out
• pulmonary bullae
• other causes of a hyperlucent hemithorax