Peripheral upper lobe collapse in adults.

Atypical (peripheral) upper lobe collapse, simulating loculated apical pleural effusion or other localized pleural disease, occurs when the collapsed lobe maintains its adherence to the lateral chest wall. Fifteen such cases are known to have been reported, 12 in children (ten of them infants) and three in adults. Two additional cases, occurring in adults with carcinoma of the bronchus, are presented here. In one case, adherence of the visceral to the parietal pleura was shown to be due to malignant infiltration. In both cases, the margination of the collapsed lobe, which on images resembles apical pleural disease, was attributed to hyperexpansion of the superior segment of the lower lobe.