Altered distribution of Pneumocystis carinii pneumonia during radiation therapy.

The radiographic findings of Pneumocystis carinii pneumonia (PCP) are various. The typical findings are diffuse, bilateral, symmetric, finely granular, or reticular infiltrates. In patients taking aerosol pentamidine, atypical findings may be the first manifestation. One interesting radiologic finding of PCP is that the pneumonia may spare the irradiated lung. We report PCP developed in a patient undergoing irradiation for lung cancer. High-resolution CT revealed diffuse, bilateral, and symmetric ground-glass opacities with septal thickening in both lungs; however, the radiation port was spared and appeared as the "photographic negative of post-radiation pneumonia." The distribution of the pneumonic infiltrates was altered by radiotherapy.