Bullous lung disease mimicking pneumothorax in focused thoracic ultrasound

Editor,

We read with interest the recent letter ‘Lessons from lung ultrasound’ by Ashton-Clearly et al. ¹ and article ‘Pitfalls in the ultrasonographic diagnosis of pneumothorax’ by Retief. ² Both groups discuss the challenges of using thoracic ultrasonography to diagnose pneumothorax in complex critically ill patients with multiple pathologies, and suggest reasons why focused thoracic ultrasonography using point-of-care protocols may not detect pneumothorax in some patients. We would like to highlight the opposite point, namely that ultrasonographic mimics of pneumothorax also exist, which may lead to misdiagnosis and iatrogenic harm from unnecessary treatment.

Intensivists in the UK typically gain basic accreditation in focused thoracic ultrasound via the Core Ultrasound in Intensive Care (CUSIC) programme. This teaches that ultrasound is recognised by absence of lung sliding (in B and M modes), presence of a lung point and absence of lung pulse. Absence of lung sliding alone is not sufficient to confirm a pneumothorax, as this can be explained by many causes including adherence of the visceral and parietal pleura in inflammatory pathologies, endobronchial intubation or mechanical ventilation with ultra-low tidal volumes.

Our group has recently encountered two young patients presenting with acute dyspnoea, hypotension and hypoxia. In both cases, focused ultrasound by experienced CUISC mentors using the modified BLUE protocol ³ demonstrated sonographic findings consistent with pneumothorax, with absence of lung sliding, absence of B lines and presence of a lung point. Both patients were known to be heavy smokers of cannabis, one of whom had a prior diagnosis of bullous lung disease resulting from this. In both cases, subsequent chest CT demonstrated the presence of giant anterior bullae underlying the upper and lower BLUE points, which were subsequently found to be responsible for the ultrasonographic appearance of presumed pneumothorax.

Distinguishing bullae from pneumothorax in the acute phase can be difficult whether based on clinical examination, plain film radiology or ultrasound. This is particularly so in the resuscitation room setting, when little background history is available about the patient and their physiology is decompensating rapidly, leaving no opportunity for a CT of the chest. Presence of B lines has been reported to distinguish giant bullae from pneuomothorax, ⁴ although in our cases these were not present. In very severe bullous emphysema, visceral pleura may be so thin that no lung sliding is detectable. ⁵ Presence of a lung point is also not specific to pneumothorax, as this may be mimicked by a pulmonary bleb, ⁵ as in our cases. Misdiagnosis may have serious consequences; unstable patients with bullous lung disease would tolerate unnecessary intercostal drains very poorly.

Whilst we are unable to provide a solution to this ultrasound conundrum, we highlight this case to remind point-of-care sonographers of the complexities of thoracic ultrasound in some emergency department and intensive care patients. We echo the call of Ashton-Cleary et al. for improved point of care ultrasound governance and regular review of cases by experienced radiologists, ¹ and anticipate that this will be the standard laid down by the next iteration of the Guidelines for the Provision of Intensive Care Services (GPICS).