Sclerosing hemangioma of the lung. Immunohistochemical demonstration of mesenchymal origin using antibodies to tissue-specific intermediate filaments.

A case of pulmonary sclerosing hemangioma of the lung was studied by light microscopy and indirect immunofluorescence using tissue-specific antibodies against intermediate filament subunits. All the tumor cells stained positively and exclusively with antivimentin antibodies thus indicating their mesenchymal origin. In addition, positive staining with cytokeratin antibodies was observed in cells lining cystic spaces and elongated slit-like spaces were occasionally encountered throughout the tumor, disclosing residual epithelial elements. Using brightfield microscopy, the keratin-positive areas were identified as distorted alveolar spaces lined by hyperplastic respiratory epithelium entrapped within the tumor. It is proposed that these entrapped epithelial elements may account for the conflicting results obtained by different investigators in previous attempts to determine the histogenesis of this tumor.