Fleischner Society

apical cap

Pathology.—An apical cap is a caplike lesion at the lung apex, usually caused by intrapulmonary and pleural fibrosis pulling down extrapleural fat (^,17) or possibly by chronic ischemia resulting in hyaline plaque formation on the visceral pleura (^,18). The prevalence increases with age. It can also be seen in hematoma resulting from aortic rupture or in other fluid collection associated with infection or tumor, either outside the parietal pleura or loculated within the pleural space (^,19).

Radiographs and CT scans.—The usual appearance is of homogeneous soft-tissue attenuation capping the extreme lung apex (uni- or bilaterally), with a sharp or irregular lower border (^,Fig 6). Thickness is variable, ranging up to about 30 mm (^,17). An apical cap occasionally mimics apical consolidation on transverse CT scans.