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.
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 .
In the vast majority of cases, blebs remain asymptomatic. Occasionally they are thought to rupture resulting a pneumothorax.
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 .
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.
Blebs appear as small (<1 or 2 cm) subpleural air spaces, located most frequently at the lung apices. They have thin, almost imperceptible walls.
Key differential considerations include:
- bulla: thin wall (<1 mm), usually considered larger than blebs (>1 or 2 cm)
- pulmonary cyst: wall thickness 1-3 mm
- pneumatocele: deeper within the lung