Multifocal micronodular pneumocyte hyperplasia in the absence of tuberous sclerosis complex: A case report.

Multifocal micronodular pneumocyte hyperplasia (MMPH) is rare in the absence of tuberous sclerosis complex (TSC). We report a genetically confirmed TSC-negative case in a 50-year-old male patient with numerous bilateral ill-defined ground-glass nodules found on chest computed tomography. The nodules were distributed predominantly in the upper and middle lung zones and showed a centrilobular distribution. The nodules measured 1-15 mm in diameter, and some abutted pleural surfaces. Because several nodules showed slight enlargement (1-2 mm) over 1 year, a diagnostic surgical biopsy was performed. Histopathology confirmed MMPH, showing a single layer of type II pneumocyte proliferation with intra-alveolar macrophages. This case demonstrates that extensive hyperplasia in MMPH can cause lesions to contact the interlobar or visceral pleura, which may be mistaken for lymphangitic spread on computed tomography, and highlights the importance of histopathological correlation to clarify imaging findings.