Vascular leiomyoblastoma of the stomach -- Observations supporting its origin from Zimmermann's pericyte

Gastric leiomyoblastoma with small mesenteric metastasis in a 44-year-old man has been studied by light and electron microscopy. Histologically, the tumor, having "epithelioid" tumor cells mixed with spindle leiomyomatous cells, was rich in blood vessels and focally simulated hemangiopericytoma. Electron microscopy revealed the tumor cells in variable stages of differentiation from poorly differentiated polygonal cells to smooth muscular cells. The intermediate cells had numerous cytoplasmic processes which interlocked each other. In addition, an intimate association was noted between the tumor cell processes and the small vessels including capillaries. With the recent characterization of the pericyte as a pluripotent mesenchymal cell that may serve as a precursor to the vascular smooth muscle cell, the present observations support the view that some leiomyoblastomas originate from the pericyte of Zimmermann. Leiomyoblastoma may be placed between hemangiopericytoma and glomus tumor in the spectrum of pericytic tumors.