Posterior urethral valves: SAQ

This neonate has posterior urethral valves presenting with the Potter sequence. The antenatal oligohydramnios and bilateral hydronephrosis, the respiratory distress from pulmonary hypoplasia, the palpable bladder to the umbilicus, the absent stream, and the ultrasound findings of bilateral hydronephrosis with a thick-walled bladder and a dilated posterior urethra form the hallmark presentation. The correct first step was taken in passing a urethral catheter, which is the first therapeutic intervention in any obstructive uropathy. The high urine output of 6 mL per kg per hour after decompression is a post-obstructive diuresis, and the hyperkalaemia, the metabolic acidosis, and the elevated creatinine reflect the renal dysplasia and the acute kidney injury. [3]

Question 1 (10 marks)

Outline the immediate and early management of this neonate, including the investigations needed to confirm the diagnosis and plan the definitive treatment. [3]

The immediate management begins with the airway and breathing, because the antenatal oligohydramnios and the current respiratory distress with a saturation of 88 percent in air signal pulmonary hypoplasia. I would provide respiratory support with continuous positive airway pressure or intubation and ventilation as clinically indicated, because this boy can die of respiratory failure before the renal problem is addressed. The urethral catheter has correctly been passed and must be maintained on free drainage to keep the bladder decompressed and the renal perfusion improved. [3]

The post-obstructive diuresis is the next priority. A urine output of 6 mL per kg per hour depletes the intravascular volume and drags out sodium and potassium, so I would replace the fluid and electrolytes hour by hour, guided by the urine output, the weight, and the biochemistry, until the self-limiting diuresis settles. The hyperkalaemia of 6.2 millimoles per litre is treated with the standard neonatal protocol, including an assessment for cardiac instability, calcium gluconate if there are ECG changes, insulin and glucose, salbutamol, and sodium bicarbonate for the metabolic acidosis. I would involve the nephrology team early and ready the renal replacement therapy pathway if the disturbance is severe or refractory. [3]

I would start prophylactic antibiotics with trimethoprim at 2 mg per kg at night, because the catheter and the obstructed system carry a high risk of urinary tract infection, which would compound the existing renal damage. The serum creatinine of 110 micromoles per litre on day 3 reflects a combination of maternal creatinine transfer and the intrinsic renal dysplasia, so I would monitor the trend over the first weeks rather than relying on any single early value. [1]

The definitive investigation is the micturating cystourethrogram, or MCUG, which is the diagnostic gold standard. It shows the dilated posterior urethra with an abrupt narrowing at the level of the valves, the thick-walled trabeculated bladder, and any associated vesicoureteral reflux. I would arrange the MCUG once the neonate is stable and the catheter is in place, with antibiotic cover around the procedure. The DMSA scan is deferred until the neonate is older and the acute situation has settled, because it maps the cortical function and the degree of dysplasia. [1]

The definitive treatment is the endoscopic valve ablation, performed once the neonate is stable, the renal function is optimised, and the urethra is large enough for a safe cystoscopy. The catheter is maintained until the ablation, and the upper tracts are reassessed by ultrasound afterward. If the neonate is too small or too unwell for an ablation, a temporary vesicostomy decompresses the bladder at low pressure until the boy grows enough for a safe procedure. [1]

Question 2 (10 marks)

Describe the long-term complications of posterior urethral valves and the principles of the follow-up and surveillance for this child. [2]

The dominant long-term complication is progressive chronic kidney disease. Robinson and colleagues showed in their population-based cohort that up to 30 to 50 percent of boys with valves progress to CKD over childhood and adolescence despite successful valve ablation, because the renal dysplasia was established in utero. The CKD may progress to end-stage kidney disease and the need for dialysis or transplantation, which makes the life-long nephrology surveillance essential. [2]

The single best predictor of the long-term renal outcome is the nadir creatinine in the first year of life. Coleman and colleagues established that a nadir below 0.8 mg per decilitre, which is about 70 micromoles per litre, predicts a favourable outcome, while a higher value predicts progression to CKD. This boy's day-3 creatinine is elevated, and his nadir over the first year will be the key prognostic marker, so I would measure the creatinine regularly in the first year and counsel the family according to the nadir. [8]

The valve bladder is the second key complication. The thick-walled, low-compliance bladder persists after ablation, because the bladder muscle learned to contract against the obstruction. The high storage pressures damage the upper tracts, the boy empties incompletely and wets by day, and the residual urine seeds recurrent infection. The bladder function is assessed by urodynamics after the ablation, and the management is tailored to the pattern, with an anticholinergic such as oxybutynin at 0.2 to 0.4 mg per kg per dose and, if that fails, clean intermittent catheterisation. [3]

The other complications include recurrent urinary tract infection from the residual bladder dysfunction, hypertension from the renal dysplasia or the hyperfiltration injury, and failure to thrive from the CKD. The surveillance includes the regular blood pressure monitoring, the serial creatinine and the estimated GFR, the urinalysis for proteinuria, the periodic DMSA scan to assess the cortical function, and the urodynamic studies to guide the bladder management. [2]

An ACE inhibitor or an angiotensin receptor blocker is commenced if hypertension or proteinuria develops, to slow the hyperfiltration injury. The transition to adult nephrology and urology care is planned in adolescence, because the CKD risk and the valve bladder persist into adulthood. The family is counselled that the valve ablation is the beginning of the management, not the end, and that the kidney and the bladder will be checked for life. [2]