The 'dark bronchus' sign: HRCT diagnosis of Pneumocystis carinii pneumonia.

We report the importance of the 'dark bronchus' sign in the diagnosis of uniform, diffuse ground glass opacification on high resolution computerized tomography (HRCT). This sign is useful to identify diffuse ground glass opacity on HRCT in cases of Pneumocystis carinii pneumonia who may present with a normal or equivocal chest radiograph in the early course of disease.