posterior urethral valves
Summary
Posterior urethral valves (PUV) are congenital obstructive membranous folds in the posterior urethra of male infants, representing the most common cause of severe lower urinary tract obstruction in newborn males. They lead to bladder outlet obstruction, which can cause hydronephrosis, renal dysplasia, and oligohydramnios if severe enough in utero. Diagnosis is often made prenatally via ultrasound showing bilateral hydronephrosis, a distended bladder, and oligohydramnios, or postnatally with voiding cystourethrogram (VCUG).
Detail
Posterior urethral valves result from abnormal folds of tissue in the posterior urethra (typically at the level of the verumontanum) that obstruct urine outflow, occurring almost exclusively in males due to the presence of a prostatic urethra. This obstruction causes a spectrum of downstream effects: bladder wall hypertrophy/trabeculation, vesicoureteral reflux, bilateral hydronephrosis, and renal dysplasia. Severe in-utero obstruction can lead to oligohydramnios, which in turn causes pulmonary hypoplasia (a major cause of neonatal mortality) and Potter sequence-like features (limb deformities, flattened facies).
Clinically, prenatal ultrasound may reveal a distended, thick-walled bladder ("keyhole sign" due to a dilated posterior urethra), bilateral hydroureteronephrosis, and oligohydramnios. Postnatally, infants may present with a palpable abdominal mass (distended bladder), weak urinary stream, urinary tract infections, or renal failure. In older children, symptoms of PUV may be more subtle, включая voiding dysfunction, urinary incontinence, or recurrent UTIs.
Diagnosis is confirmed with a voiding cystourethrogram (VCUG), which shows a dilated posterior urethra, a thickened/trabeculated bladder, and possible vesicoureteral reflux. Renal ultrasound assesses the degree of hydronephrosis and renal parenchymal damage.
Management involves prompt bladder decompression via a urethral or suprapubic catheter, followed by definitive treatment with transurethral ablation/fulguration of the valves via cystoscopy. Long-term follow-up is essential given the risk of chronic kidney disease, as many patients (especially those with severe presentation) may progress to end-stage renal disease requiring dialysis or transplantation. Bladder dysfunction ("valve bladder syndrome") with poor compliance and high storage pressures can persist even after valve ablation, contributing to ongoing renal damage.
This condition is high-yield for boards as a classic cause of bilateral hydronephrosis in male infants, oligohydramnios leading to pulmonary hypoplasia, and a key differential in neonatal renal failure or abdominal mass.
Sources
- First Aid for the USMLE Step 1
- Campbell-Walsh Urology
- UpToDate: Posterior urethral valves
- Nelson Textbook of Pediatrics
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.