Spontaneous rupture of an aortic aneurysm into the left renal vein. A diagnostic challenge. Rupture of an aortic aneurysm into a renal vein presents a rare and difficult diagnostic problem. Often, therapy is delayed because the patient is thought to have a urologic problem. In this instance, CT scan provided useful clues leading to the diagnosis of this entity, and its rapid treatment. To our knowledge, this is the first CT scan done in a patient with aorto-renal vein fistula. 