The hallmark finding of PCP on HRCT scans is ground-glass attenuation, which is present in more than 90% of patients and represents an exudative alveolitis. The term ground-glass refers to parenchymal opacification, which does not obscure the underlying pulmonary architecture. This usually occurs in a bilateral, symmetric, predominantly perihilar distribution and may be geographic or mosaic in appearance, with areas of normal lung adjacent to areas of affected lung. Thickening of interlobular septa (due to edema) and foci of consolidation may be associated.
