Table 1.

Fleischner Society Definitions of Cystic Changes Seen on Chest Radiographs

Lesion	Definition
Cyst	Thin-walled (<2 mm), spherical parenchymal lucency interfaced with normal lung.
Cavity	Gas-filled space within pulmonary consolidation, mass, or nodule, typically thick walled (>2 mm) and more irregularly shaped than cysts.
Bulla	Spherical focal lucency, ≥1 cm in diameter, bounded by a thin wall (usually <1 mm). It is usually accompanied by emphysematous changes in the adjacent lung.
Bleb	Cystic air space bounded by a thin wall adjacent to the visceral pleura, typically <1 cm in size.
Pneumatocele	Approximately round, thin-walled, air-filled space in the lung. Most frequently caused by infections, trauma, or aspiration of hydrocarbon fluid and is usually transient.

Definitions from Reference 88.