Pulmonary calcification caused by Pneumocystis carinii pneumonia. A clinicopathological study of 13 cases in acquired immune deficiency syndrome patients.

Pulmonary microcalcifications were identified in 13 patients with Pneumocystis carinii pneumonia (PCP) and acquired immune deficiency syndrome (AIDS). Several patterns of calcification were noted including bubbly, plate-like, elongate, and conchoidal forms. All calcifications contained P. carinii cysts within them as demonstrated by Grocott's methenamine silver stain. In eight of the 13 cases, the typical intra-alveolar exudate of P. carinii was absent. Therefore, the calcifications were the only histopathologic indication of prior P. carinii infection. The above-mentioned calcifications are important because in five cases they occurred without a prior diagnosis of PCP, subsequent therapy, or prophylaxis. This indicates that in some patients there is destruction of P. carinii organisms with subsequent calcification, and this can occur without therapy.