Prenatal sonographic predictors of postnatal pyeloplasty in fetuses with isolated hydronephrosis.

Objective: To define prenatal sonographic predictors of ureteropelvic junction obstruction requiring postnatal pyeloplasty, in fetuses with isolated hydronephrosis.

Methods: Retrospective data on prenatal sonographic parameters were compared between patients who had been diagnosed prenatally with hydronephrosis and either underwent postnatal pyeloplasty for ureteropelvic junction obstruction (n = 39) or were treated conservatively (n = 30).

Results: Significant differences between the surgically and conservatively treated patients were found for mean anterior-posterior renal diameter (22.8 ± 8.6 vs 14.2 ± 5.9 mm, respectively, p < 0.0001) and parenchymal thickness (5.9 ± 2.8 vs 8.1 ± 2.6 mm, p = 0.009). Anterior-posterior diameter >14 mm was the best single predictor of the need for surgery (area under the ROC curve, 0.817), with sensitivity 77%, specificity 69%, positive predictive value (PPV) 77% and negative predictive value (NPV) 69% (β = 1.17, 95%CI = 1.07-1.28, p < 0.001). Mean ratio of anterior-posterior diameter to parenchymal thickness was significantly higher in the postnatal pyeloplasty group (5.4 ± 4.5 vs 2.1 ± 1.4, p = 0.0001). A ratio >2.1 had a sensitivity of 87% and specificity of 65% for the need for surgery (area under the curve 0.822, PPV 79%, NPV 77%; β = 1.92, 95%CI = 1.16-3.17, p < 0.001).

Conclusion: In cases of prenatal isolated hydronephrosis, the pelvic anterior-posterior diameter and parenchymal thickness may predict the need for postnatal pyeloplasty. A ratio of >2.1 of pelvic anterior-posterior diameter to parenchymal thickness suggests ureteropelvic junction obstruction and supports the use of more intensive prenatal and postnatal surveillance.