RADIOLOGY: KIDNEY: Case# 32912: RENAL ANGIOMYELOLIPOMA. This 40-year-old female presented with a spontaneous left renal hemorrhage. This scan is requested for further evaluation. There is a complex left upper pole renal mass containing extensive fat density, consistent in appearance with angiomyolipoma. A small amount of soft tissue density is seen within the mass, as well as some soft tissue stranding around the kidney. Most likely, this represents resolving hematoma. Since the previous study, there has been near total interval resolution of hematoma. There is moderate splenomegaly, with numerous splenic vein collaterals. Renal angiomyelolipoma is a benign mesenchymal tumor composed of abnormal blood vessels which lack smooth muscle, elastic tissue, and fat in varying amounts. 80% of tumors are found in middle-aged women and are solitary and unilateral. The other 20% are found in patients with tuberous sclerosis. These are usually multiple and bilateral and commonly detected during childhood and infancy. These patients may also have multiple renal cysts and cutaneous, retinal, and cerebral hamartomas. Because of the fragile walls of the vessels, these tumors are prone to hemorrhage which can be massive. Solitary tumors are surgically removed. Demonstration of fat density within the tumor on CT is considered diagnostic since renal cell carcinomas do not contain fat detectable by CT. Typical findings include nodules and strands of soft tissue density representing smooth muscle and vascular components. In addition, vasculature may show remarkable contrast enhancement. Tumors may be as small as 1cm but may be as large as 20cm and extend into the perirenal tissues and lymph nodes.