Aortocaval fistulae presenting with renal failure: CT diagnosis

We describe two patients who presented with acute renal failure secondary to aortocaval fistulae, which were demonstrated by computed tomography (CT) and confirmed at surgery. Renal function rapidly returned to normal following appropriate surgery. In addition to the expected CT findings of early equal enhancement of the inferior vena cava and aorta and dilation of the inferior vena cava, there was early enhancement of dilated renal veins despite poor contrast enhancement of the kidneys. It is postulated that retrograde flow of blood from the aortocaval fistula may cause renal impairment secondary to renal venous hypertension.