Posterior Urethral Valves

The most common cause of fetal bladder outlet obstruction is posterior urethral valves. Ultrasound examination shows a dilated, thick-walled bladder, often with dilatation of the proximal urethra-the "keyhole" sign. Renal findings may include hydronephrosis, cortical cysts, or kidneys that are small and echogenic. Ureteral dilatation is also common. Oligohydramnios before midgestation confers an extremely poor prognosis and prompts consideration for fetal vesicoamniotic shunt therapy. Important factors before vesicoamniotic shunt placement are that the anomaly appears isolated, that the fetus is male, that the chromosomal microarray (or karyotype) results are normal, and urinary analyte values obtained via serial vesicocentesis suggest relatively preserved renal function. Families need to be counseled about the high rates of acute and chronic morbidity associated with this condition.