Fig. 2

Histologic and immunohistochemical characteristics of case 2. (Top left): prominent hematopoietic islands were observed inside vascular spaces with typical anastomosing pattern. (Upper middle left): larger angiomatous spaces with less prominent anastomosing pattern were observed at the periphery of the largest lesion simulating cavernous hemangioma next to a large vessel. (Lower middle left): some lesions were extending to the sinus or peri-renal fat tissue entrapping adipocytes. (Lower left): numerous smaller lesions (circles) with similar histologic features were observed throughout renal parenchyma. (Top right): endothelial cells were D2-40-negative and CD31-positive (inset), while intervascular septa were highlighted by SMA-positive cells (upper middle right). (Lower middle right): c-kit staining highlighted increased number of mast cells all over the lesion. (Bottom right): Although at low power magnification the margins of the lesion seemed non-infiltrative, CAM5.2 immunostaining revealed locally infiltrative features with entrapment of renal tubules (inset) (3,3′ diaminobenzidine as chromogen, hematoxylin as counterstain, original magnifications 40X, 100X, 400X)