Congenital anomalies of the kidney and urinary tract: SAQ

This neonate has posterior urethral valves, the most common cause of lower urinary tract obstruction in male infants. The antenatal oligohydramnios and bilateral hydronephrosis, the palpable distended bladder, the poor urinary stream, and the ultrasound findings of bilateral hydronephrosis with a thick-walled bladder and dilated posterior urethra are the hallmark presentation. The immediate priority was the correct one, to pass a urethral catheter to decompress the obstruction. The serum creatinine of 95 micromoles per litre on day 3 is concerning, because it reflects a combination of maternal creatinine transfer and the intrinsic renal dysplasia from the chronic obstruction in utero. [9]

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. [12]

The immediate management has already begun with the urethral catheterisation, which is the first therapeutic intervention in any obstructive uropathy. The catheter must be maintained and monitored for output, because the relief of the back-pressure improves the renal perfusion. I would assess the airway and breathing, because the antenatal oligohydramnios raises the risk of pulmonary hypoplasia, and the tachypnoea may reflect respiratory distress rather than a primary renal problem. I would monitor the renal function with serial creatinine, the electrolytes, and the acid-base balance, because the neonate may have a metabolic acidosis, hyperkalaemia, or fluid overload from the renal dysplasia. [9]

I would start prophylactic antibiotics, because the catheter and the obstructed system carry a high risk of urinary tract infection, which would compound the existing renal damage. I would involve the paediatric urologist and the nephrologist early. The definitive investigation is the micturating cystourethrogram, or MCUG, which shows the dilated posterior urethra and the valve leaflets, and it confirms the diagnosis. I would arrange the MCUG once the neonate is stable and the catheter is in place, with antibiotic cover around the procedure. [12]

The renal ultrasound has already shown the bilateral hydronephrosis and the thick-walled bladder, which are consistent with the diagnosis. A DMSA scan is deferred until the neonate is older and the acute situation has resolved, because it maps the cortical function and the degree of dysplasia. The definitive treatment is the endoscopic valve ablation, performed once the neonate is stable and the renal function is optimised, and the catheter is maintained until the ablation. [9]

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. [8]

The long-term complications of posterior urethral valves are dominated by the progressive chronic kidney disease. Robinson and colleagues showed in their population-based cohort study that a substantial proportion of boys with valves progress to CKD over childhood and adolescence, with the risk influenced by the nadir creatinine in the first year, the degree of bilateral dysplasia, and the bladder function after ablation. The CKD may progress to end-stage kidney disease and the need for renal replacement therapy, which makes the life-long nephrology surveillance essential. [8]

The bladder dysfunction, the valve bladder, is the second key complication. The valve bladder is a thick-walled, low-compliance bladder that stores poorly and generates high storage pressures that damage the upper tracts. The bladder function is assessed by urodynamics after the valve ablation, and the management includes clean intermittent catheterisation and anticholinergic medication such as oxybutynin to improve the bladder storage and to protect the upper tracts. The bladder dysfunction persists and may worsen over time, which makes the urology follow-up as important as the nephrology follow-up. [9]

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 DMSA scan to assess the cortical function, and the urodynamic studies to guide the bladder management. The transition to adult nephrology care is planned in adolescence, because the CKD risk persists into adulthood. [8]