Cavitation or cyst formation is well documented but uncommon in Pneumocystis infection of the lungs. In this image there is a subpleural smooth walled cavity. Lesions of this type may rupture through the visceral pleura producing pneumothorax. Beneath that cavity is a larger cavity with a ragged irregular lining consisting mostly of foamy exudate containing the Pneumocystis organisms. The mechanism of cavity/cyst formation in Pneumocystis infection is not well understood. The lung parenchyma is diffusely consolidated and pale reflecting alveolar filling by foamy exudate containing the Pneumocystis organisms.