ABSTRACT
Posterior urethral valves (PUVs) are the most common congenital anomaly causing bladder outlet obstruction in boys, with an incidence of 1 in 5000 to 1 in 8000 male births. At five to six weeks' gestation, the orifice of the mesonephric duct normally migrates from an anterolateral position in the cloaca to Müller's tubercle on the posterior wall of the urogenital sinus. PUVs comprise 10% of prenatally diagnosed obstructive uropathy, and two-thirds of cases of PUV are diagnosed antenatally. Typical findings include bilateral hydroureteronephrosis, a distended bladder and a dilated prostatic urethra, called a 'keyhole' sign. Prenatally, PUV, prune belly syndrome, urethral atresia and bilateral high-grade vesicoureteric reflux all have similar appearances. Fetal intervention is indicated in suspected cases of PUV if the fetal urine is hypotonic and associated with oligohydramnios, with the goal of preventing life-threatening pulmonary hypoplasia. Close follow-up is important in PUV after valve ablation.
