Linear opacities as a feature of pneumocystis pneumonia.

Linear opacities are generally regarded as uncommon in pneumocystis pneumonia. The authors' experience suggests this is not so, and that such opacities may have diagnostic value. Chest radiographs of 22 episodes of uncomplicated pneumocystis pneumonia were reviewed and linear opacities were present in nine episodes (41%). Similar opacities were present in 11 out of 121 cases of other pneumonias (9%). Characteristically the opacities are related to the acute illness, usually one to three in number, predominantly basal, 1-4 cm long and less than 2 mm thick. Other radiographic signs of pneumocystis pneumonia were present in all cases. The pathogenesis of these linear opacities is uncertain, but it is possible that they result from areas of sub-segmental atelectasis. The frequency of such linear opacities is much greater in pneumocystis pneumonia (four times) than in other pneumonias and they therefore have some diagnostic value.