Magnetic resonance urographic parameters for predicting the need for pyeloplasty in infants with prenatally diagnosed severe hydronephrosis.

Purpose: Treatment in infants with prenatally diagnosed, severe hydronephrosis remains controversial. We measured anatomical parameters using magnetic resonance urography to create a pelvic index ratio, which we correlated with outcome to assess its value.

Materials And Methods: We reviewed 35 cases of prenatally diagnosed severe hydronephrosis, including grade III in 19 and grade IV in 16. By 6 weeks after birth all patients had undergone repeat ultrasonography, diuretic renography and magnetic resonance urography. Magnetic resonance urography was used to measure the distance (D) from the bottom of the lowest renal calyx to the ureteropelvic junction and the total longitudinal length (L) of the caliceal system. The pelvic index ratio, defined as D/L, assesses the level at which the ureter inserts into the renal pelvis.

Results: All cases were initially managed conservatively. Pyeloplasty was required in 16 kidneys (mean patient age +/- SD 7.5 +/- 3.9 months) because of deterioration in renal function. All patients were well at a mean followup of 3.8 years. The remaining 19 cases continued to be managed conservatively. By a mean of 5.4 years spontaneous resolution of prenatally diagnosed severe hydronephrosis had occurred in 7 of 19 cases, while 12 were downgraded to grades I-II. The mean pelvic index ratio in surgical cases was 0.26 +/- 0.13 and in nonsurgical cases it was 0.12 +/- 0.11, indicating that ureters inserted significantly higher in surgical cases (p = 0.0012). Of 9 kidneys with a pelvic index ratio of greater than 0.3 pyeloplasty was required in 8, while 10 of 12 with a pelvic index ratio of less than 0.1 were managed conservatively.

Conclusions: Pyeloplasty is likely to be required if the pelvic index ratio is greater than 0.3 and conservative management is likely to succeed if the ratio is less than 0.1. The pelvic index ratio can be calculated easily even in the neonatal period. It appears to be prognostic for pyeloplasty in cases of prenatally diagnosed, severe hydronephrosis.