Oliguria, anuria and urinary obstruction: Case

This male infant presents anuria with a palpable distended bladder and bilateral hydronephrosis, the classic presentation of posterior urethral valves complicated by an acute kidney injury and hyperkalaemia. The absence of any urine for 18 hours meets the anuria threshold of complete absence for 12 hours or more by the KDIGO criteria. The palpable suprapubic mass that does not empty with gentle pressure is a distended bladder, and the ultrasound confirms the lower tract obstruction with the dilated posterior urethra and the thick-walled bladder. The potassium of 6.7 mmol per litre with peaked T waves is immediately life-threatening, and the metabolic acidosis reflects the accumulating acid from the failing, obstructed kidney. ^[1]

Clinical findings

The pattern is that of a lower urinary tract obstruction from posterior urethral valves, complicated by an acute kidney injury with hyperkalaemia. The palpable distended bladder and the dilated posterior urethra on the ultrasound localise the obstruction to the bladder outlet, and the bilateral hydronephrosis confirms the upper tract effect of the raised pressure. The anuria, the elevated creatinine, and the hyperkalaemia confirm the acute kidney injury, and the peaked T waves on the ECG mark the immediate cardiac risk. The irritability and the tachypnoea reflect the metabolic acidosis and the uraemia. The diagnosis is posterior urethral valves, to be confirmed by a voiding cystourethrogram once the infant is stabilised. ^[6]

The differential at presentation includes the other causes of anuria in a male infant. A bilateral renal anomaly such as bilateral renal agenesis or severe bilateral renal dysplasia produces anuria but without a distended bladder and with absent or abnormal kidneys on the ultrasound. Acute tubular necrosis from a perinatal insult produces anuria but without the obstruction and with a normal-calibre urinary tract on the ultrasound. The palpable bladder and the dilated posterior urethra settle the differential in favour of posterior urethral valves, and the immediate management is the same regardless: the decompression of the obstruction. ^[6]