LUNG CYSTS ASSOCIATED WITH PNEUMOCYSTIS-CARINII PNEUMONIA - RADIOGRAPHIC CHARACTERISTICS, NATURAL-HISTORY, AND COMPLICATIONS

OBJECTIVE. The purpose of our study was to characterize the radiographic features of thin-walled air-filled structures (cysts) related to Pneumocystis carinii pneumonia in a large series of patients, determine the natural history of the cysts, and test the hypothesis that the cysts are associated with an increased risk of pneumothorax. MATERIALS AND METHODS. Of 100 patients with proved pneumocystis pneumonia, 34 (34%) had cysts shown on chest radiographs. The size, number, and location of the cysts and their natural history and association with pneumothorax were determined. A control group consisting of a random sample of 30 patients was selected from the 66 patients who had pneumocystis pneumonia but no cysts to assess the frequency of pneumothorax in this population. RESULTS. Of 34 patients with cysts, 32 (94%) had multiple cysts that were 1.0-5.0 cm in diameter. Most cysts were in the upper part of the lungs. Most patients had complete or partial resolution of the cysts after the acute episode of pneumonia. Pneumothoraces occurred in 12 (35%) of the 34 patients with cysts, but in only two (7%) of the 30 who did not have cysts (p = .007). CONCLUSION. Cysts related to pneumocystis pneumonia are usually multiple, occur most often in the upper parts of the lungs, and tend to decrease in size or resolve after the acute stage of the infection. In patients with pneumocystis pneumonia, the prevalence of pneumothorax is significantly higher in those who have cysts than in those who do not. The cysts are similar to pneumatoceles and the high prevalence of pneumothorax may be due to the subpleural location of some cysts.