Benign fibrous histiocytoma of the renal capsule

The first case of benign fibrous histiocytoma of the renal capsule is reported in a male aged 44 years. The tumor had its point of origin in the renal capsule. Histologically, the tumor was composed of intersecting fascicles of fibroblastic cells forming a loose crisscross or "storiform" pattern. Electron microscopic studies of tumor cells revealed intermediate filaments and membrane-bound collagen fibers which continued to extracellular collagen bundles. This deep seated fibrous histiocytoma had a more prominent storiform pattern and fewer secondary elements such as xanthoma cells than cutaneous ones.