Antenatal hydronephrosis: changing concepts in diagnosis and subsequent management.

The overall incidence of genitourinary abnormalities during routine prenatal US screening is 2±9 per 1000 births [1±5], with a male to female ratio of 2 : 1 [3]. The spectrum of genitourinary abnormalities detected in utero is extremely varied; most affected fetuses (50±87%) have hydronephrosis [6±8]. The remaining anomalies include multicystic dysplastic kidney, autosomal recessive polycystic kidney disease, renal agenesis and dysplasia. Other abnormalities that have been described include bladder exstrophy, adrenal hyperplasia, imperforate anus, cloacal abnormalities, neuroblastoma, mesoblastic nephroma and genital abnormalities [6]. The accuracy of the prenatal diagnosis of hydronephrosis has been compared with postnatal evaluations and a false-positive diagnostic error rate of 9±22% is reported [9,10]. This overestimation may be because there are no accepted criteria for the diagnosis of hydronephrosis, and in utero resolution during fetal development [11].