Pulmonary bullae (singular: bulla) are focal regions of emphysema with no discernible wall which measure more than 1 or 2 cm in diameter. Some use the term pulmonary bleb for a similar lesion less than 1 or 2 cm, whereas others use both the terms bleb and bulla interchangeably.
They are often subpleural in location and are typically larger in the apices. In some cases, bullae can be very large and result in compression of adjacent lung tissue. A giant bulla is arbitrarily defined as one that occupies at least one third of the volume of a hemithorax. When large, bullae can simulate pneumothorax.
The most common cause is paraseptal emphysema but bullae may also be seen in association with centrilobular emphysema.
- spontaneous pneumothorax