We describe two patients who presented with acute renal failure second
ary to aortocaval fistulae, which were demonstrated by computed tomogr
aphy (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 aort
a and dilation of the inferior vena cava, there was early enhancement
of dilated renal veins despite poor contrast enhancement of the kidney
s. It is postulated that retrograde flow of blood from the aortocaval
fistula may cause renal impairment secondary to renal venous hypertens
ion.