Angiomyolipomas are lesions that are comprised of varying amounts of blood vessels, smooth muscle and fat. These are benign (non-cancerous) lesions that grow slowly and are detected incidentally. They usually do not cause any symptoms. However, in some instances, angiomyolipomas can become quite large and cause abdominal or flank pain. Lesions that are larger than 4 cm in diameter can bleed and cause bloody urine. The other major complication with larger lesions include impingement on normal kidney tissue leading to decreased kidney function. Lastly, all patients with angiomyolipomas should be evaluated for possible rare condition called 'tuberous sclerosis'. This includes careful skin, eye and neurologic examination. Brain imaging may be required as well.