Pulmonary blebs are small subpleural thin walled air containing spaces, not larger than 1 or 2 cm in diameter (with the precise limit varying by source). Their walls are less than 1 mm thick. If they rupture, they allow air to escape into pleural space resulting in a spontaneous pneumothorax.

Epidemiology

Blebs are a very common finding in otherwise normal individuals. They are often found in young patients. They are more common in thin patients and in cigarette smokers 1.

Clinical presentation

In the vast majority of cases, blebs remain asymptomatic. Occasionally they are thought to rupture resulting a pneumothorax.

Pathology

Blebs are thought to occur as a result of subpleural alveolar rupture, due to overload of the elastic fibers.

Pulmonary bullae are, like blebs, cystic air spaces that have an imperceptible wall (less than 1 mm). The difference between blebs and bullae is generally considered to be their size, with the delimiter being either 1 or 2 cm in diameter, depending on the source. Blebs may, over time, coalesce to form bullae 1.

Radiographic features

Pulmonary blebs are not visible on chest x-rays, but can seen on the lung windows of CTs. In patients who have had a pneumothorax secondary to a ruptured bleb, it is often difficult, if not impossible to locate since it has decompressed is surrounded by pneumothorax and has deflated adjacent lung.

CT

Blebs appear as small (<1 or 2 cm) subpleural air spaces, located most frequently at the lung apices. They have thin, almost imperceptible walls.

Differential diagnosis

Key differential considerations include: