Transitional hydronephrosis of the newborn and infant.

Between 1986 and 1988, 187 hydronephrotic renal units were discovered antenatally in 134 subjects and confirmed in the neonatal period. Of these cases 119 (64%) were due to anomalies of the ureteropelvic junction. The remainder (36%) were due to various congenital uropathic conditions. Investigation consisted of renal ultrasonography, voiding cystourethrography and diuretic renography with 99mtechnetium-diethylenetriaminepentaacetic acid augmented with furosemide. Of the 119 renal units 36 (30%) underwent pyeloplasty, while 42 (35.7%) were considered normal without obstruction or dilatation. In 41 units (34.3%) diuretic renography showed partial obstruction or dilatation without obstruction that washed out readily with furosemide. Serial renal ultrasonography and renography were performed in these patients. A 12-month followup showed improvement or stabilization in 80% of the renal units and deterioration to significant obstruction in 20%. In attempting to identify the renal units that were most at risk for deterioration, it was realized that the initial ultrasound had a predictive role. None of the mildly hydronephrotic units deteriorated, whereas 14% of the moderately hydronephrotic and 32% of the markedly hydronephrotic units showed further deterioration. However, whether diuretic renography initially demonstrated partial obstruction or dilatation without obstruction, the ultimate outcome could not be predicted. Based on this experience an algorithm is proposed for the evaluation and management of antenatally detected hydronephrosis with currently available imaging techniques.