10th January 2024

Diagnosis 

A diagnosis of a pneumothorax can be made clinically with the identification of appropriate clinical signs; however, these signs are not always present. In any patient presenting with sudden onset dyspnoea and pleuritic chest pain pneumothorax should remain as part of the differential diagnosis. The mainstay of confirming a pneumothorax diagnosis comes from imaging.

A subset of patients with large pneumothoraces or tension pneumothoraces are haemodynamically unstable, and quick diagnosis is required. In this setting, if available, bedside ultrasound can be utilised to confirm the diagnosis with subsequent rapid initiation of management (see management section). However, the majority of patients who present are haemodynamically stable, and it is these patients who can undergo less urgent, non-bedside imaging.

PA Chest X-ray

Image Source: Wikimedia Commons (2017). Spontaneous pneumothorax, Licensed under a creative commons licence. Available for free at: https://upload.wikimedia.org/wikipedia/commons/b/b1/Spontanpneumothorax.jpg (Accessed on: 21 June 2022).

The posterior-anterior (PA) erect chest x-ray is the mainstay of diagnostic imaging in stable patients (and can also be utilised in unstable patients at the bedside if ultrasound is not available). It allows identification of the pathology and size of the pneumothorax, which is important in considering subsequent management strategies.

Features that can be seen on a PA erect chest x-ray are:

• Visible lung edge
• Lung markings absent beyond visible lung edge (and the absence of lung markings to the chest wall should prompt the clinician to look for pneumothorax evidence)
• Radiolucent space beyond visible lung edge, i.e. darker, from increased air without lung parenchyma.
• Increased distance between rib spaces on affected hemithorax.
• Mediastinal shift and tracheal shift away in cases of tension pneumothorax.
• Subcutaneous emphysema.

A “simple” pneumothorax on PA chest x-ray is the presence of pneumothorax without mediastinal shift. A tension pneumothorax is diagnosed when mediastinal shift is identified either clinically or on diagnostic imaging.

In order to measure the size of pneumothorax present, 2 methods can be used: the American method and the British method. In the American method, it is the distance between the apex and top of the lung (cupola). The British method, and the method utilised in BTS guidelines, is the measurement of the interpleural distance at the level of hilum between the visible collapsed lung edge and chest wall. A “small” pneumothorax is typically referred to as a pneumothorax that is <2cm in size and a large pneumothorax one that is >2cm in size. However, it is important to clinically assess and correlate patients (especially those with secondary spontaneous pneumothoraces) as size of pneumothorax does not always correlate with clinical symptomatology and distress.

Flowchart adapted from guidance available at – Maskell N. British Thoracic Society pleural disease guidelines – 2010 update. Thorax. 2010;65(8):667–9. 

Gary Lee Y. Clinical presentation and diagnosis of pneumothorax [Internet]. UpToDate. 2021 [cited 2022 Jun 1]. Available from: https://www.uptodate.com/contents/clinical-presentation-and-diagnosis-of-pneumothorax?search=pneumothorax &source=search_result&selectedTitle=2~150&usage_type=default&display_rank=2#H3647761918

CT Thorax

CT Thorax can be utilised when there is diagnostic uncertainty following a PA chest x-ray or in the diagnosis of a small pneumothorax, where it should be considered the “gold standard” for evaluation of size and the underlying anatomy. CT Thorax can not only easily identify a pneumothorax, but it can also alert the clinician to any underlying changes, e.g. emphysematous lung disease or bullae, which may be related to the aetiology of the pneumothorax.

CT remains superior to chest x-ray and ultrasound in terms of accurately identifying a pneumothorax; however, it is not as readily available and exposes patients to a significant dose of radiation.

Ultrasound

Bedside pleural ultrasound can provide rapid diagnosis of pneumothorax in the unstable patient, but it is also highly sensitive for identification of small pneumothoraces.

In the normal lung utilising the straight linear array high-frequency probe, pleural ultrasound shows the lung ‘sliding’ as the patient respires. Alongside the sliding pleural ‘Z lines’ can be seen, which are vertical comet tails (artefacts) running down from the pleura.  By switching the probe into M-mode in the normal lung, the “seashore” sign can be visualised, which represents the sliding pleura moving on a motionless chest wall. Several signs on ultrasound can suggest the presence of a pneumothorax:

• Absence of lung sliding.
  • On M mode – this can be referred to as the “barcode” sign.
• Absence of comet tail artefacts. These artefacts are lost due to the build-up of air within the pleural space.
• Lung point sign. This nearly 100% specific sign for pneumothorax refers to identifying the junction between sliding lung and non-sliding lung. This is useful in small pneumothoraces as in larger-sized pneumothoraces, entire lung collapse can occur, and therefore, global absence of lung sliding is noted.
  • This sign can also be helpful in estimating size of the pneumothorax if present.
• Absence of lung pulse.