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]