POSTERIOR URETHRAL VALVES PUVS

Posterior urethral valves (PUVs)
Definition
Abnormal congenital mucosal folds in the prostatic (posterior) urethra causing lower urinary tract obstruction.

Classification
- Type I (90 95%) Membranes arise from the distal lateral aspect of the verumontanum,1 which extend distally and anteriorly to fuse in the midline.
- Type II Longitudinal folds extending from the verumontanum to bladder neck.
- Type III A ring-like membrane found distal to the verumontanum.

Incidence
1 in >5000 males

Aetiology
Normal male urethra has small, paired lateral folds (plicae colliculi) which are found between the lateral, distal edge of verumontanum and lateral urethral wall. PUVs probably represent a congenital overgrowth of these folds, due to abnormal insertion of Wolffian ducts into the posterior urethra during fetal development.

Presentation
Prenatal USS features
Bilateral hydroureteronephrosis; dilated bladder and posterior urethra (keyhole sign); thick-walled bladder; oligohydramnios (reduced amniotic fluid); and renal dysplasia. Early features are associated with poor prognosis.

Newborn and infants
Respiratory distress (secondary to pulmonary hypoplasia); palpable abdominal mass (hydronephrotic kidney or distended bladder); ascites; UTI; electrolyte abnormalities; failure to thrive.

Older children
Milder cases may present later with recurrent UTI; poor urinary stream; incomplete bladder emptying; poor growth and incontinence. Risk of renal failure, vesicoureteric reflux, and voiding dysfunction (overactive or underactive bladder), also described as  valve bladder syndrome .

Associated features
POP-off valve syndrome  is seen in 20%. It describes mechanisms by which high urinary tract pressure is dissipated to allow normal renal development. It includes leaking of urine from small bladder or renal pelvis ruptures (urinary ascites), reflux into a non-functioning kidney (vesicoureteral reflux with renal dysplasia or VURD), and formation of bladder diverticuli.

Investigation
- Ultrasound scan of renal tract.
- Micturating cystourethrogram: distended posterior urethra (shield-shaped); partially filled anterior urethra; bladder neck hypertrophy; lucencies representing valve leaflets; thick walled bladder (diverticuli); incomplete bladder emptying; reflux (50%).
- Isotope renal scan (MAG-3, DMSA): assesses renal function.
- Videourodynamics: allows diagnosis of associated voiding dysfunction. Management
Commence prophylactic antibiotics immediately, check serum electrolyes, and drain the bladder with a paediatric feeding tube. If there is improvement, cystoscopy and transurethral ablation of valve (cuts at 5 and 7 o'clock with electrocautery) is recommended (complications include urethral strictures). If upper tracts remain dilated with raised creatinine after bladder drainage, a temporary cutaneous vesicostomy is indicated (communicating stoma between the bladder dome and suprapubic abdominal wall, allowing free drainage of urine). An alternative is ureterostomy drainage. Valve ablation is performed at a later stage.

Prognosis
35% poor renal function; 20% develop end-stage renal failure.

Footnote
Verumontanum is tissue found on the ventral aspect of the prostatic urethra into which drain the ejaculatory ducts and prostatic utricle.