MICROSCOPIC DESCRIPTION: Sections of lung show multiple discrete foci of stellate parenchymal fibrosis containing plump oval cells with grooved nuclei and a mixed chronic inflammatory cell infiltrate including numerous eosinophils. No refractile foreign body material is seen. The adjacent alveolar spaces contain modest numbers of pigment respiratory macrophages. There is no evidence of atypia, dysplasia or malignancy. Immunohistochemically cells stain CD1a+, S-100+ and CD68-. Special stains are negative for micro-organisms.

DIAGNOSIS: Lung, wedge resection: Langerhan's cell histiocytosis.