Pyelovenous backflow or veno-caliceal valve fistula?

A 70-year-old male with urinary bladder carcinoma was admitted for follow-up. Retrograde pyelography demonstrated transfer of contrast medium into the left renal vein in two independent sessions. The absence of hematuria and a negative CT scan ruled out a classical veno-caliceal fistula. The presence of a veno-caliceal valve fistula into the left renal vein was hypothesized.