We describe a unique benign tumor of the kidney in a 93-year-old man. Microscopically the tumor was composed of an intimate intermixture of epithelial component and smooth muscle tissue, which formed the stroma of the tumor. In some parts the epithelial cells in adenomatous tubular formations were endowed with clear snouts. These clear snouts had a blister-like quality and grew on the secretory cells lining the tubules. No atypias, mitoses, or pleomorphism were present in the tumor. The muscular component consisted of poorly cellular, HMB-45-negative, leiomyomatous bundles, which greatly differed from that of angiomyolipoma. It encircled the whole tumor and intimately intermingled with the epithelial component. These leiomyomatous bands formed focally abortive vessels, which had incomplete and irregular walls and lacked an elastic layer. Even more interesting was a peculiar vascularization of the tumor. All epithelial tubular structures of the tumor revealed an intimate association with small capillaries. A fine labyrinth of the capillaries rimmed the rows of the epithelial cells. To the best of our knowledge this tumor differs from all previously described.

Department of Pathology Faculty Hospital Pilsen Czech Republic

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