A tumor composed of myofibroblasts: an ultrastructural study.

A subcutaneous tumor of the right temporal region of head was removed from an 8-year-old boy. This tumor was studied by light and electron microscopy. He was found to have had a retroperitoneal inflammatory fibrous histiocytoma which had been excised seven years ago. The subcutaneous tumor histologically consisted of spindle cells in fascicles, which did not arrange in a storiform or herring-bone pattern. Electron microscopically, this tumor was chiefly composed od myofibroblasts. electron microscopy is essential to determine the cell types of a tumor and we have classified this tumor as a tumor of myofibroblasts. The relationship between the retroperitoneal tumor and the head tumor was discussed.