Supranormal renographic differential renal function in congenital hydronephrosis: fact, not artifact

Children with unilateral hydronephrosis, who had been prospectively examined with diethylenetriaminepentaacetic acid (DTPA) and dimercapto-succinic acid (DMSA) renography, were evaluated to determine whether supranormal renographic differential renal function exists.

A total of 54 children with congenital single system hydronephrosis underwent abdominal ultrasound, voiding cystourethrogram, and DTPA and DMSA renal scans. None had abnormalities of the bladder or contralateral kidney. Differential renal function greater than 55% was defined as supranormal.

Of the 54 patients 15 (28%) with a median age of 4 months (range 0.5 to 66) were identified with supranormal renographic renal function on either DTPA or DMSA. Supranormal renographic renal function was detected by DMSA in 9 cases (mean 57+/-2%), DTPA in 8 (mean 58+/-2%) and both in 2 (mean 57+/-2%). Average function demonstrated in the 15 patients was 55+/-3% (range 51 to 62) with DMSA which was not different from that found with DTPA (mean 55+/-4%, range 46 to 61%). The kidneys with supranormal renographic renal function were significantly larger than hydronephrotic controls according to longitudinal parenchymal area on DMSA. Mean followup was 20 months for 13 patients, with 8 of 13 (62%) undergoing pyeloplasty. Followup DTPA renal scans available in 9 children revealed persistent supranormal function in 6, despite pyeloplasty in 3.

Supranormal renographic differential renal function does exist in congenital hydronephrosis and when found the kidneys are consistently enlarged. The position of supranormal renographic renal function in the management algorithm of hydronephrosis remains to be elucidated as it does not appear to be a benign prognostic factor.