Alveolar atypical hyperplasia

Mammary gland Hyperplastic alveolar nodules Atypical epithelial hyperplasia Lobular hyperplasia Intraductal hyperplasia Hyperplastic terminal duct... 

Alveolar septa may show some degree of expansion due to capillaritis, edema, and/or interstitial fibrosis (84,85). Capillaritis, characterized by neutrophils within the septa, is usually focal and of mild to moderate intensity. Diffuse or prominent capillaritis, or vasculitis of larger blood vessels is atypical, and if present, suggests another disease process. When interstitial fibrosis is present, it too is usually patchy and mild. Type II pneumocytes may show hyperplasia and reactive atypia in response to alveolar damage. In some cases, hyaline membranes are seen focally (85). Ultrastructural studies have shown fragmentation of alveolar septal basement membranes and wide gaps between endothelial cells (90). 

Kerr KM, Carey FA, King G, Lamb D. Atypical alveolar hyperplasia relationship with pulmonary adenocarcinoma, p53, and c-erB-2 expression. J Pathol 1994 174 249-256. 

Westra WH, Baas 10, Hruban RH, et al. K-ras oncogene activation in atypical alveolar hyperplasias of the human lung. Cancer Res 1996 56 2224-2228. 

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