Lung biopsy in Pneumocystis carinii pneumonia: a histopathologic study of typical and atypical features.

This study of 36 patients with Pneumocystis carinii pneumonia emphasizes a spectrum of histopathologic changes that have not been classically considered features of the infection. These atypical microscopic findings were present in 69% of the cases as defined in this retrospective examination. As expected, the suggestion of the correct diagnosis of Pneumocystis carinii pneumonia on the basis of a frozen section and without the aid of appropriate special stains was extremely difficult in the majority of biopsies. It is important for the pathologist to maintain the possibility of this infection in his differential diagnosis when he examines a pulmonary biopsy from a patient who is immunologically compromised.