Ultrasound grade of hydronephrosis and severity of renal cortical damage on 99mtechnetium dimercaptosuccinic acid renal scan in infants with unilateral hydronephrosis during followup and after pyeloplasty

Purpose: We performed ultrasonography and (99m)technetium dimercaptosuccinic acid (DMSA) renal scan in infants with unilateral hydronephrosis during followup and after pyeloplasty to examine the correlation of ultrasound hydronephrosis grade with the severity of renal cortical damage and assess the recovery of renal function in the obstructed kidneys after surgery. Materials and Methods: We studied 80 boys and 19 girls with unilateral hydronephrosis detected in the first year of life, including 75 (76%) in whom it was detected prenatally. Ultrasound images were graded according to the Society for Fetal Urology grading system. The severity of renal cortical damage was assessed by DMSA renal scan. Absolute function of the right and left kidneys was estimated by DMSA uptake and relative DMSA uptake was calculated by the formula, relative uptake = uptake in obstructed kidney/total uptake in right and left kidneys x 100%. Results: On ultrasonography grades 1 to 4 hydronephrosis were diagnosed in 9, 21, 19 and 50 kidneys, respectively. On DMSA renal scan cortical damage was detected in 10 kidneys (53%) with grade 3 and 49 (98%) with grade 4 hydronephrosis but not in kidneys with grade 1 or 2 disease. Dysfunction in the obstructed kidney, defined as relative DMSA uptake less than 40%, was noted in 13 patients with grade 4 hydronephrosis. Relative DMSA uptake significantly increased after successful pyeloplasty compared with preoperative uptake (44% +/- 2% versus 40.1% +/- 2%, p <0.01). Conclusions: Ultrasound grading of hydronephrosis correlates with the severity of cortical damage or the decrease in renal function on DMSA renal scan. Differential renal function on DMSA renal scan may be a useful and less invasive tool for determining surgical indications and examining changes in renal function after surgery.