Multifocal micronodular pneumocyte hyperplasia in a man with tuberous sclerosis.

We report a peculiar case of multifocal micronodular pneumocyte hyperplasia (MMPH) occurring in a 43-year-old man with tuberous sclerosis. Computed tomography of the chest demonstrated multiple micronodules, measuring up to 5 mm in size, present bilaterally in the lung fields, with no cystic change. Histologically, a proliferation of type II pneumocytes without the typical nulclear atypia lined the thickened alveolar septa in an adenomatoid pattern. Proliferation of immature smooth muscle cells suggestive of LAM was not observed. The characteristic findings of the positive immunohistochemical stains for cytokeratin and surfactant apoprotein A and B, and negative stains for HMB-45, alpha-1 smooth muscle actin, desmin, p53 and carcinoembryonic antigen confirmed the presence of alveolar lining cells in each MMPH lesion. Since the MMPH was observed in a male and did not appear to possess malignant potential, the MMPH appears to be a hamartomatous proliferation occurring in a male with tuberous sclerosis that is separate from lymphangiomyomatosis (LAM) which is related to estrogen and progesterone receptors.