Computed tomography correlation in atypical (peripheral) right upper lobe collapse: the minor fissure as an explanation for the pleural-based density.

Peripheral right upper lobe collapse describes the unusual plain film finding in which the collapsed lobe simulates a peripheral, pleural-based mass. Most investigators have postulated that the peripheral opacity is explained by the interface between the superior segment of the lower lobe and the posterior aspect of the collapsed upper lobe, which does not swing as far medial as in the normal pattern of collapse. In our patient, using computed tomography (CT) correlation, we demonstrated that the finding is explained by the interface between the middle lobe and the anterior aspect of the collapsed upper lobe.