Increased renal function in kidneys with ureteropelvic junction obstruction: fact or artifact? Assessment by quantitative single photon emission computerized tomography of dimercapto-succinic acid uptake by the kidneys.

PURPOSE

We evaluated whether increased differential renal function on the pentetic acid (DTPA) renogram represents elevated renal function in obstructed kidneys.

MATERIALS AND METHODS

In 10 patients with unilateral ureteropelvic junction obstruction and a differential function of 53% or greater on the DTPA renogram of the obstructed kidney we performed quantitative single photon emission computerized tomography of dimercapto-succinic acid uptake by the kidneys.

RESULTS

The absolute uptake of dimercapto-succinic acid was significantly higher in the obstructed kidneys compared to the contralateral normal kidneys (30.0% +/- 7.8 versus 25.3% +/- 8.2, t = 3.6, p < 0.01, respectively). The elevated absolute uptake in the obstructed kidneys was due to an increased functional volume compared to the contralateral normal kidneys (126.0 +/- 69.7 cc versus 102.3 +/- 59.2 cc, t = 4.4, p < 0.01, respectively).

CONCLUSIONS

The results suggest that increased relative renal function in hydronephrotic kidneys due to ureteropelvic junction obstruction is not an artifact of the DTPA renogram. It may represent a compensatory mechanism that sometimes may overcompensate resulting in a paradoxical hyperfunctioning kidney.