Posterior urethral valves: Case

This boy has posterior urethral valves presenting in the late, milder pattern. The two febrile urinary tract infections, the weak and dribbling stream, the daytime wetting, the growth faltering, the blood pressure at the 95th percentile, and the elevated creatinine for age are the clinical features, and the MCUG confirms the diagnosis with the dilated posterior urethra and the abrupt narrowing at the level of the valves. The bilateral grade 3 vesicoureteral reflux and the thick-walled bladder with a significant post-void residual are the expected associated findings. [1]

Clinical findings

The key clinical findings are the dilated posterior urethra with the abrupt narrowing on the MCUG, the bilateral moderate hydronephrosis, the thick-walled bladder with the post-void residual, the bilateral grade 3 reflux, the two febrile infections, the blood pressure at the 95th percentile, and the creatinine of 78 micromoles per litre in a 3-year-old. The growth on the 15th centile for weight and the blood pressure at the 95th percentile both signal the early chronic kidney disease and the hyperfiltration injury, which are the central concerns in a late-presenting boy. [2]

The differential for a boy with bilateral hydronephrosis and a thick-walled bladder includes posterior urethral valves, prune belly syndrome, a neurogenic bladder, and severe bilateral reflux. The MCUG showing the dilated posterior urethra with the abrupt narrowing is the discriminator that confirms the valves, because none of the mimics produce this sign. The normal abdominal wall excludes prune belly syndrome, and the absent spinal stigmata and the lower-limb neurology make a neurogenic bladder unlikely. [1]

Investigations and diagnosis

The diagnosis is posterior urethral valves with bilateral grade 3 vesicoureteral reflux and an early chronic kidney disease. The investigation pathway is complete, with the renal ultrasound showing the hydronephrosis and the thick-walled bladder, the MCUG confirming the valves and the reflux, and the blood tests showing the elevated creatinine and the blood pressure at the 95th percentile. A DMSA scan is arranged to map the cortical function and the degree of dysplasia and any scarring, because the two febrile infections may have left renal scars that compound the dysplasia. [2]

The creatinine of 78 micromoles per litre is elevated for a 3-year-old, which reflects the renal dysplasia established in utero. The boy is past the neonatal period, so his creatinine is no longer confounded by the maternal transfer, and his nadir creatinine over the coming year will be the key prognostic marker. Coleman and colleagues established that a nadir below 0.8 mg per decilitre, about 70 micromoles per litre, predicts a favourable outcome, so this boy's current value places him in the higher-risk group that needs close surveillance. [8]

Management and outcome

The definitive management is the endoscopic valve ablation, performed once the boy is assessed and stable. The valves are cut with a small cystoscope to restore the outflow, and the catheter is maintained for a few days afterward. The bilateral grade 3 reflux is managed with prophylactic antibiotics such as trimethoprim at 2 mg per kg at night, to prevent further febrile infection and renal scarring, and the reflux is monitored for spontaneous resolution. [1]

The valve bladder is the focus of the long-term urology care. The thick-walled, low-compliance bladder with the significant post-void residual stores poorly and generates high pressures that damage the upper tracts. The bladder function is assessed by urodynamics after the ablation, and Tang and colleagues emphasised the role of the urodynamics in guiding the management. The poorly compliant bladder is treated with an anticholinergic such as oxybutynin at 0.2 to 0.4 mg per kg per dose, and clean intermittent catheterisation is added if the medication fails to achieve a low-pressure bladder. [6]

The chronic kidney disease surveillance runs in parallel. The blood pressure at the 95th percentile and the elevated creatinine signal the early CKD and the hyperfiltration injury, so an ACE inhibitor or an angiotensin receptor blocker is commenced to lower the blood pressure and to slow the hyperfiltration injury. Robinson and colleagues showed that up to 30 to 50 percent of boys with valves progress to CKD over childhood and adolescence, which is why the surveillance is life-long. The blood pressure, the proteinuria, the serial creatinine, the periodic DMSA scan, and the urodynamics form the surveillance programme, and the transition to adult nephrology and urology care is planned in adolescence. [2]

The family is counselled that the valve ablation is the beginning of the management, not the end, because the kidneys and the bladder were affected before birth. The boy will need life-long surveillance, and some boys develop kidney problems over the years even after a perfect operation. The immediate plan is the valve ablation, the bladder assessment, and the blood pressure control, and the long-term plan is the coordinated nephrology and urology follow-up with the planned transition. [8]