SO‐CALLED SCLEROSING HEMANGIOMA OF THE LUNG

Sclerosing hemangioma of the lung (SHL) was investigated immunohistochemlcally, histochemically and ultrastructurally with reference to cellular components associated with the histologic pattern: cuboidal cells in the papillary type, round cells in the solid type, flat cells in the hemorrhagic type and stromal cells in the sclerotic type. immunohistochemically, cuboidal cells were positive for CEA, cytokeratin and EMA, whereas other cells were positive for EMA and vimentin. immunoreactive factor‐VIII‐related antigen was confined to endothelial cells. Histochemically, cuboidal cells displayed alkaline phosphatase activity, but round cells showed ATPase activity. However, in spite of these different histochemical and immunohistochemical properties, morphological continuity was clearly revealed in immunostained sections; direct connection of spaces lined by cuboidal and fiat cells, direct contact between cuboidal and stromal cells, and EMA expression of round cells associated with luminal structures were evident Ultrastructurally, cuboidal cells were like alveolar cells. Flat and stromal cells showed microvillous protrusions and a discontinuous basement membrane, but some cells contained lamellar bodies. Solid cellular sheets consisted of various cells intermediate between cuboidal and flat or stromal cells. Direct apposition among these cells was evident This morphological continuum confirms that each of these cell types are components of SHL as a whole. SHL may thus be merely sclerotic hemorrhagic alveolar cell tumor.