Posterior Urethral Valves

Posterior Urethral Valves is a topic covered in the 5-Minute Pediatric Consult.

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Basics

Description

  • A posterior urethral valve (PUV) is an embryologic remnant of tissue in the urethra that causes obstruction of the lower urinary tract during fetal development.
  • This obstruction results in short- and long-term structural abnormalities and physiologic dysfunction in the genitourinary system (kidney, ureter, bladder, and urethra).

Epidemiology

  • Most common cause of lower urinary tract obstruction in males
  • The incidence is estimated to be between 1:3,000 and 1:8,000 live male births.
  • PUVs are the cause of 10% of urinary obstructions diagnosed prenatally.
  • Approximately 24–45% of children born with PUV will exhibit renal insufficiency during childhood and approximately 50% progress to end-stage renal disease in 10 years.
  • PUV accounts for up to 17% of the cases of children with end-stage renal failure.
  • Children with PUVs receive 25% of pediatric renal transplantations.

Risk Factors

Genetics

  • Majority of cases are isolated and occur sporadically.
  • Rarely, cases have been reported in siblings.
  • No causative genetic abnormality has yet been found.

Pathophysiology

  • The valve is a leaflet or membrane of thin connective tissue that extends from the anterior urethral lip to the verumontanum posteriorly, obstructing the normal flow of urine through the urethra. This results in an elongated urethra and upstream dilation in the urinary system.
  • PUVs exist in a spectrum of severity, from being lethal in utero to subtle symptoms late in childhood.
  • PUVs are commonly associated with intrinsic renal dysplasia. Studies have demonstrated that dysplastic renal parenchyma at time of birth is permanent.
  • Renal injury may be caused by persistent high pressure (reversible) as well as renal dysplasia (irreversible).
  • Commonly associated pathophysiologic findings in children with PUV include (i) hydroureteronephrosis, (ii) dilated bladder with trabeculations and/or diverticulum, and (iii) vesicoureteral reflux.
  • PUVs may result in early or late bladder dysfunction with decreased compliance and increased voiding pressure that affect both the storage and expulsion of urine. Additionally, PUVs expose the upper tract of the urinary system to increased pressure, which leads to worsening renal function over time.
  • Neonates may have respiratory failure (due to pulmonary hypoplasia) and limb and facial malformations (due to oligo- or anhydramnios).

Etiology

  • Multiple theories exist as to the embryologic origin of PUVs.
  • Male urethral development is usually complete by 14 weeks’ gestation; PUV formation is presumed to occur prior to this point.
  • Possible embryologic origin of PUVs include (i) presence of an obstructing membrane in the posterior urethra, (ii) overgrowth or abnormal folding during normal urethral development, (iii) abnormal integration of the wolffian ducts into urethral development, or (iv) abnormal persistence of the urogenital membrane.

Commonly Associated Conditions

  • Genitourinary: hydroureteronephrosis, vesicoureteral reflux, bladder wall thickening and diverticulum, obstructive urinary symptoms, urinary ascites in cases of bladder rupture, perirenal urinoma in cases of renal collecting system rupture, renal dysplasia
  • Varying degrees of renal insufficiency may also be present in patients from birth through adulthood.
  • PUV has been associated with other congenital anomalies of the genitourinary tract, prune belly syndrome, imperforate anus, and congenital heart disease.

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