Malignant fibrous histiocytoma of the renal capsule. Light and electron microscopic study of a rare tumor.

This light microscopically pleomorphic tumor, which occurred in the renal capsule of 35-year-old female was diagnosed as a malignant fibrous histiocytoma. Ultrastructurally, the tumor showed two major components; fibroblast-like and histiocyte-like cells. This report stresses the rarity of such neoplasm in the kidney and also the usefulness of electron microscopy in establishing the diagnosis.