Posterior urethral valves

Key points

Antenatal considerations

PLUTO trial

Vesicoamniotic shunt at 24-25 weeks

Underpowered, not selective

No difference in renal outcomes, damage done -

May improve outcomes in terms of pulmonary hypoplasia if done before canalicular phase at 26 weeks

Not known whether late presentation has better outcomes

Best to deliver as close to term as possible, as best for lungs

Predictors of poor outcome:

1. Oligohydramnios

2. Echogenic kidneys

3. Foetal urine osmolality >300

4. Foetal urine B2 microglobulin >20mg/L

Pop off mechanism sites:

1. VUR

2. Bladder diverticula

3. Patent urachus

4. Calyces

Urinary ascites suggests a pop-off mechanism has been used, this is a good prognostic indicator as it is protective of the kidneys

Can present late with urosepsis, failure to thrive and renal failure

Always ask about urinary flow in male children with UTI

Management

For very premature babies - can leave urethral catheter for a long time for baby to grow

Vesicostomy is last resort

Vesicostomy (Blocksom) should be done at dome of bladder - use urachus to identify. If anterior wall is used, posterior wall will prolapse

Refluxing ureterostomy is alternative - bring out one loop of ureter through skin - allows backflow valve to protect both kidneys

Clean-intermittent catheterisation (CIC) use has been described in PUV. As the urethra is sensate, it requires an early start to allow the child and family to adapt to it

Effects on the bladder

Valve bladder syndrome - High pressure, trabeculated bladder, polyuria with dilute urine due to renal failure

Bladder function changes over time -

1 year - filling: bladder capacity reduced but normal compliance. Voiding: biphasic or polyphasic detrusor pattern with high pressures and incomplete emptying

5 years - one of 3 patterns:

1. Normal

2. Same as at 1 year

3. Detrusor myogenic failure - weak contractility and increased capacity

Predictors of long-term renal impairment

• Maternal oligohydramnios

• Proteinuria

• Bilateral vesicoureteric reflux

• Impaired daytime urinary continence after the age of 5 years

Proteinuria is normal in the evening, so take samples in morning

ACEi or ARB can reduce proteinuria in the absence of hypertension

Standard scenario

Antenatal finding of bilateral hydroureteronephrosis in a male foetus

Differential diagnosis:

PUV

Bilateral VUR

Anterior urethral valves - ventral - 40% bulbar urethra, 30% penoscrotal junction, 30% penile urethra

Urethral stenosis or agenesis

Antenatal bilateral HN

Look for:

Oligohydramnios

Pulmonary hypoplasia

Potters sequence

Cortex on kidneys, cysts, echogenic kidneys

Offer counselling

After birth:

Treat pulmonary hypoplasia

Start trimethoprim

Place non-balloon catheter

Monitor for diuresis and -

Creatinine rise of >3umol/L day for first 5 days after catheter (creatinine velocity) is predictor of worse renal outcomes

U+E after 24 hour

Give sodium supplements, renal diet (low K+)

Post natal USS and MCUG at 48 hours - cover with antibiotics

Look for dilated posterior urethra, reflux, trabeculated bladder

(Also do for male unilateral HN)

Timing of ablation: When creatinine stabilised

9.5Fr resectoscope - cold knife

Catheter for 24h after

Follow up:

3 months: Check cystoscopy + circumcision (based on parental choice and if UTIs)

USS + DMSA + GFR at 3 months

Start oxybutynin

Nadir creatinine = lowest creatinine in the 1st year after diagnosis - >75umol/l is predictive of renal failure

Follow up in joint nephro-urology clinic. If worsening upper tract dilatation, infections - do urodynamics

Flow rate after toilet training

Video urodynamics + DMSA + GFR at age 5

If rising creatinine and UTI post resection in infant -

Urology MDT

Cover with antibiotics

Cystoscopy with on table cystogram + delayed film - look for incomplete resection, VUR/VUJO

Video urodynamics

If poor voiding post op - encourage double voiding if toilet trained - Can do CIC but may be difficult as sensate urethra - in contrast to spina bifida

If unable do SPC

Offer circumcision

May need bladder augment when older

If VUJO do refluxing side to side Ureterovesicostomy

Nephrostomy last resort

Urodynamic pattern - Mario DeGennaro BJU

Young children - small overactive bladder

Normalises as they age

Detrusor failure as adolescents

References

Essentials of Pediatric Urology, 3rd edition, 2022, Chapter 9 Posterior Urethral Valves and Other Urethral Abnormalities

De Gennaro M, Capitanucci ML, Mosiello G, Caione P, Silveri M. The changing urodynamic pattern from infancy to adolescence in boys with posterior urethral valves. BJU Int. 2000 Jun;85(9):1104-8. doi: 10.1046/j.1464-410x.2000.00700.x. PMID: 10848705.

Percutaneous vesicoamniotic shunting versus conservative management for fetal lower urinary tract obstruction (PLUTO): a randomised trial

Morris, Rachel K et al. The Lancet, Volume 382, Issue 9903, 1496 - 1506