Multifocal micronodular pneumocyte hyperplasia associated with tuberous sclerosis: differentiation from multiple atypical adenomatous hyperplasia.

We report a peculiar case of multifocal micronodular pneumocyte hyperplasia (MMPH) in a 54-year-old woman with tuberous sclerosis complex (TSC) diagnosed during antituberculous treatment. Findings were initially detected by chest computed tomography (CT) to check for complication of pulmonary tuberculosis. Chest CT demonstrated multiple small nodules with ground-glass opacity, measuring up to 5 mm diameter, presenting in the bilateral lung fields, without cystic change. Because the differentiation from multiple atypical adenomatous hyperplasia (AAH) was necessary, we finally performed a diagnosis of MMPH based on specimens obtained by video-assisted thoracoscopic surgery. Histologically, type II pneumocytes without nuclear atypia lined the thickened alveolar septa and proliferated papillary structures. There was no proliferation of immature smooth muscle cells suggestive of lymphangioleiomyomatosis. Although immunohistochemical stains for cytokeratin and surfactant apoprotein A and B were positive for alveolar lining cells in each MMPH lesion, those for HMB-45, alpha-smooth muscle actin, p53 and carcinoembryonic antigen were negative. We must consider MMPH as part of the differential diagnosis along with multiple AAH when multiple small nodules with ground-glass opacity were observed on chest CT in patients with TSC.