Posterior urethral valves: Viva

Branch 1: Classification and pathophysiology

The candidate should define posterior urethral valves as congenital membrane-like folds in the male posterior urethra that obstruct the urinary outflow, and should state that they are the most common cause of lower urinary tract obstruction in male infants, occurring only in boys at approximately 1 in 4000 to 8000 live male births. A strong candidate classifies the valves by the Young system: the Type I valve, two leaflets fusing in the midline from the verumontanum, is by far the most common, the Type II valve is now regarded as non-obstructing and rare, and the Type III valve is a distal diaphragm with a central pinhole. [1]

If the examiner presses on the pathophysiology, the candidate should trace the urine. The valve blocks the outflow, the bladder thickens into a hard muscular wall, and the back-pressure travels up the ureters to cause bilateral hydronephrosis and renal dysplasia. The reduced fetal urine output causes oligohydramnios, which in the most severe cases produces the Potter sequence with pulmonary hypoplasia. The candidate should name pulmonary hypoplasia as the reason the worst-affected boys die of respiratory failure at birth, and should explain that the valve bladder persists after ablation. [1]

Branch 2: Investigation and immediate management

If asked about the investigations, the candidate should state that the micturating cystourethrogram is the diagnostic gold standard, showing the dilated posterior urethra with an abrupt narrowing at the level of the valves, the thick-walled trabeculated bladder, and any associated reflux. Khondker and colleagues validated the posterior urethral morphology on the initial MCUG as a reliable predictor, confirming its central diagnostic role. The renal ultrasound is the first-line imaging test, and the DMSA and MAG3 scans assess the cortical function and the drainage respectively. [9]

The candidate should state that the first therapeutic intervention is always a urethral catheter to decompress the bladder, which improves the renal perfusion within hours. The candidate should describe the management of the biochemical disturbances of renal failure, the use of prophylactic antibiotics with trimethoprim at 2 mg per kg at night, and the watch for the post-obstructive diuresis in the hours after decompression. The definitive treatment is the endoscopic valve ablation, performed once the neonate is stable, with a temporary vesicostomy for the boy too small or unwell for the ablation. [1]

Branch 3: The valve bladder and the long-term renal outcome

If the examiner moves to the long-term outlook, the candidate should name chronic kidney disease as the dominant complication. Robinson and colleagues showed that up to 30 to 50 percent of boys progress to CKD despite successful ablation, because the renal dysplasia was established in utero. The candidate should state that the nadir creatinine in the first year is the single best predictor, and that a nadir below 0.8 mg per decilitre, about 70 micromoles per litre, predicts a favourable outcome. [8]

A strong candidate discusses the valve bladder, the thick-walled, low-compliance bladder that persists after ablation and generates high storage pressures that damage the upper tracts. The bladder function is assessed by urodynamics, and the management includes anticholinergic medication such as oxybutynin and, if that fails, clean intermittent catheterisation. The candidate should conclude that the surveillance runs for life, with the blood pressure, the proteinuria, the serial creatinine, and a planned transition to adult nephrology and urology care, because the CKD risk persists into adulthood. [8]