Fig. 3

Pathological findings of the resected tumor. Grossly, the tumor was continuous with the renal capsule and adherent with the perirenal fat. The border is well demarcated. The cut surface is dark red with hemorrhage (a). Histologically, the tumor is mostly hemorrhagic with a less amount of spindle cells and fat in the septa (hematoxylin and eosin, original magnification ×100) (b). Immunohistochemically, the spindle-shaped cells are reactive with the human melanoma black-45 antibody, demonstrating the melanosome-associated antigen, (c) but negative for cytokeratin (antibody clone AE1/AE3). The cyst wall lacks epithelial lining, unlike angiomyolipoma with epithelial cyst (d)