When is it necessary to perform nuclear renogram in patients with a unilateral neonatal hydronephrosis?

Purpose: To examine whether anteroposterior(AP) pelvic diameter on postnatal renal ultrasound scan (US) can predict both initial differential renal function (DRF) and deterioration in DRF in patients with prenatally diagnosed hydronephrosis. Methods: One hundred and thirty-three patients diagnosed with a unilateral prenatal hydronephrosis, confirmed postnatally, were evaluated. We tried to find the cutoff values for initial AP diameter and change in AP diameter based on initial DRF and renal outcome. Reduction of 5% or more was considered as deterioration in function. All patients had an initial US scan at a mean age of 1.62 weeks (1-4) and nuclear renogram at 13.24 weeks (7-21). All patients had a second US at a mean age of 10.58 weeks (6-19). 119 patients had a second renogram. Results: Initial mean pelvic diameter was 20.86 (11-49) mm. When AP pelvic diameter was less than 20 mm, 98.6% of all renal units had a function of ≥40%. The cutoff point for AP pelvic diameter was 19.05 when DRF was ≥45% (P < 0.001). When the reduction in hydronephrosis in pelvic diameter was analyzed to predict the initial renal function, a cutoff point of 1.3 mm decrease was found when initial renal function was ≥40% (P < 0.001). The reduction in AP pelvic diameter was 2.1 mm when initial DRF was ≥45% (P = 0.009). For all patients except 3 individuals, if there was a reduction in AP diameter or the AP diameter was stable, then no reduction in function was observed. Conclusion: When the AP pelvic diameter is less than 20 mm at presentation, DRF is normal. If the AP diameter is stable or decreases, there is unlikely to be a significant deterioration in renal function. Consequently, in selected patients, congenital unilateral hydronephrosis can be followed with serial ultrasounds.