Severe fetal hydronephrosis: the added value of associated congenital anomalies of the kidneys and urinary tract (CAKUT) in the prediction of postnatal outcome

Objective The aim of this study was to focus on fetuses diagnosed with severe hydronephrosis and correlate prenatal sonographic characteristics with postnatal outcome. Methods Cases presenting prenatally with severe hydronephrosis (anterior‐posterior renal pelvic diameter >15 mm) were collected retrospectively over a period of 11 years and divided into 2 groups: (1) isolated hydronephrosis and (2) those associated with congenital anomalies of the kidney and urinary tract (CAKUT). Results A total of 83 fetuses comprised the study group: 35 fetuses had isolated severe hydronephrosis and 48 had associated CAKUT. The mean anterior‐posterior renal pelvic diameter was 22.6 ± 8.5 mm (range 15.0‐66.0 mm). The CAKUT group was associated with a significantly increased incidence of postnatal need for surgery (17.6% vs 44.2%, P = .014), dysplastic kidney (0% vs 14%, P = .023), and total abnormal outcome (52.9% vs 86%, P = .001) in comparison with isolated severe prenatal hydronephrosis. Conclusions Severe fetal hydronephrosis has a wide postnatal clinical spectrum, which is mainly influenced by the presence of associated sonographic CAKUT findings. These clinical data have biological relevance: a genetic or environmental defect that influences multiple renal developmental processes leads to hydronephrosis but also to concomitant malformations (CAKUT) and critically influences renal prognosis. A more selective abnormal developmental process that results in isolated enlarged pelvis even to a severe extent has less influence on renal prognosis. What is already known about this topic? Fetal urinary tract dilation is the common denominator of a wide spectrum of possible uropathies. Current prenatal classifications of urinary tract dilatation rely mainly on the anterior‐posterior renal pelvic diameter (APRPD). What does this study add? CAKUT‐associated prenatal severe hydronephrosis is as independent factor for the prediction of postnatal abnormal renal outcome. Prenatal diagnosis of hydronephrosis, mainly in its severe form, should be followed by meticulous sonographic assessment of the kidneys, ureters, and urinary bladder for optimal risk assessment and parent counseling.