Posterior Urethral Valves

  • Etiology: Anterior fusion of plicae collicularis at level of verumontanum leading to urethral membrane causing variable bladder outlet obstruction
    — Types – Type I is 95%, Type II doesn’t exist, Type III is 5%
  • Imaging US Prenatal:
    — Dilated posterior urethra
    — Oligohydramnios or urinoma or urine ascites
    — Pulmonary hypoplasia due to oligohydramnios
  • Imaging US:
    — Dilated posterior urethra
    — Bladder can look normal but often is dilated with thick wall and trabeculations and diverticula
    — Occasionally bladder rupture with urinary ascites
    — Upper urinary tract bilateral hydroureteronephrosis variable and when severe can rupture with perinephric urinoma
    — Variable degree of renal damage or dysplasia from obstruction such as parenchymal thinning and cysts and abnormal echogenicity
  • Imaging VCUG:
    — Obstruction by veil-shaped valve leading to dilated posterior urethra
    — Trabeculated thick walled bladder
    — Bilateral hydroureteronephrosis from vesicoureteral reflux leads to renal damage so kidneys can be small and echogenic on US
  • DDX:
  • Complications:
    — Perinephric fluid collection (urinoma) and urinary ascites due to urinary tract rupture
    — Cystic renal dysplasia
    — At risk post-operatively for recurrent urinary tract infections due to dilated genitourinary system
    — 30-42% develop end stage renal disease and is major cause for pediatric renal transplantation
  • Treatment: Cystoscopic valve fulguration
  • Clinical:
    — Males only
    — Most common cause of bladder outlet obstruction and thus chronic renal disease in males
    — Spectrum from fetal demise to apparently normal neonate
    — Rarely can present later in childhood
    — High fetal or neonatal mortality of 30%, considerable morbidity

Radiology Cases of Posterior Urethral Valves

VCUG of posterior urethral valves
AP image from a voiding cystourethrogram (above) shows bilateral grade 5 vesicoureteral reflux, right greater than left, and a narrow pinecone-shaped bladder in the inferior midline aspect of the image. Lateral image of the urethra taken during the voiding phase of the voiding urethrogram (below) shows marked dilation of the posterior urethra and a thin lucent membrane at the transition zone where the urethra assumes a more normal caliber.
VCUG of posterior urethral valves
Oblique image from a voiding cystourethrogram (left) shows left vesicoureteral reflux up into a non-dilated left renal collecting system. The posterior urethra appears dilated. Magnified lateral image of the urethra (right) shows the dilation of the posterior urethra is due to a fixed narrowing in the posterior urethra.

Radiology Cases of Posterior Urethral Valves Causing Urine Ascites

VCUG of urine ascities
AXR scout image (left) shows centralization of mildly distended bowel loops. AP image obtained at the end of a voiding cystourethrogram (right) shows left Grade V vesicoureteral reflux. The overall density of the abdomen is increased in the interval due to contrast extravasation out of the renal collecting system and extravasated contrast is outlining loops of bowel and can be seen tracking up the right lateral aspect of the abdomen.