Multifocal micronodular pneumocyte hyperplasia in a postmenopausal woman with tuberous sclerosis

We report a peculiar case of multifocal micronodular pneumocyte hyperplasia (MMPH) without association of pulmonary lymphangioleiomyomatosis (LAM) in a 56-year-old postmenopausal woman with tuberous sclerosis. This case is surmised to be a forme fruste of tuberous sclerosis. Computed tomography demonstrated multiple micronodules, measuring up to 5 mm in size, present in the bilateral lung fields, but no cystic changes. A proliferation of pleomorphic type-II pneumocytes lining the thickened alveolar septa in an adenomatoid pattern, with an associated increase in alveolar macrophages, was observed without typical nuclear atypia. In fully developed lesions, the ingrowth of more proliferating type-II pneumocytes into the thickened alveolar septa and macrophages filling the alveolar lumens were characteristic findings. Proliferation of immature smooth muscle cells suggesting LAM was not observed. Positive immunohistochemical stains for cytokeratin, epithelial membrane antigen, and surfactant apoproteins A and B, and negative staining for HMB45, alpha-1 smooth muscle actin, desmin, and carcinoembryonic antigen confirmed the characteristics of alveolar lining cells in each MMPH lesion. MMPH associated with tuberous sclerosis in the postmenopausal woman appears to be similar to that described in premenopausal women. The present case is familial rather than sporadic and suggests no relationship between the development of MMPH and the underlying hormonal state.