Pneumonia pathogens have characteristic radiographic patterns. Which pattern is associated with Pneumocystis jirovecii pneumonia in AIDS patients?

• A. Diffuse interstitial and alveolar infiltrates
• B. Lobar consolidation
• C. Patchy alveolar consolidation
• D. Cavitary lesions

Answer: (A)

Pneumocystis jirovecii pneumonia in AIDS patients classically presents as a diffuse interstitial process. The immune deficiency allows the organism to spread widely in the lungs, leading inflammation that predominantly involves the interstitium and the alveolar spaces, which shows up on chest radiographs as bilateral, diffuse interstitial infiltrates (often with perihilar and basilar predominance). This pattern mirrors the widespread, interstitial nature of the infection, and it helps distinguish PJP from other pneumonias.

Lobar consolidation, by contrast, points to a typical bacterial pneumonia affecting an entire lobe. Patchy alveolar consolidation can occur with various causes but is less characteristic of PJP’s diffuse involvement, and cavitary lesions are more typical of tuberculosis, certain fungal infections, or infections with necrotizing processes.