Antenatal hydronephrosis and postnatal evaluation: Case

This infant has the increased-risk UTD A2-3 antenatal hydronephrosis from the ureteropelvic junction obstruction on the right. The anteroposterior diameter of 16 mm at 32 weeks exceeds the 10 mm threshold and places the fetus in the increased-risk category, and the postnatal confirmation at day 5 with the diameter of 22 mm and the dilated renal pelvis and the major and the minor calyces is consistent with the Society for Fetal Urology grade 3. The MAG3 renogram confirms the impaired drainage and the reduced split function on the right. [6]

Clinical findings

The key findings are the increased-risk antenatal category with the progressive dilatation from 8 mm at 24 weeks to 16 mm at 32 weeks, the correctly timed postnatal ultrasound at day 5 that confirmed the severe right hydronephrosis, the normal-calibre ureter that points to the ureteropelvic junction obstruction rather than the reflux, and the MAG3 renogram that showed the impaired drainage with the split function of 42 percent on the affected side. The normal blood pressure, the normal growth, and the normal creatinine are reassuring for the overall renal function. [1]

The progression of the anteroposterior diameter across the serial antenatal scans is an important finding, because the worsening dilatation suggests the progressive obstruction rather than the transient physiologic dilatation. The Nakane study showed that the antenatal grade 1 and grade 2 hydronephrosis resolves in the majority of the cases, but the progressive and the high-grade dilatation carries a higher probability of the pathology, which is why the postnatal evaluation was correctly initiated. [12]

Investigations and diagnosis

The diagnosis is the right ureteropelvic junction obstruction. The investigation pathway was correctly performed, with the postnatal ultrasound at day 5 confirming the severe hydronephrosis and the normal-calibre ureter, and the MAG3 renogram confirming the impaired drainage and the split function. The timing of the first postnatal ultrasound at day 5 was correct, because the deferred timing avoids the false negative of the neonatal dehydration in the first 48 hours. The MCUG was not performed because the normal-calibre ureter made the reflux unlikely, and the clinical picture did not suggest the posterior urethral valves. [6]

The 2021 update by Nguyen and colleagues clarified the application of the Urinary Tract Dilation classification in the postnatal period. The postnatal system uses the prefix P and cannot be interchanged with the antenatal prefix A. The increased-risk postnatal features, which include the peripheral calyceal dilatation and the ureteral dilatation and the abnormal parenchyma, trigger the further investigation. This infant had the calyceal dilatation, which warranted the MAG3 renogram. [9]

Management and outcome

The management is initially the conservative surveillance, because the split function of 42 percent on the affected side is preserved and above the threshold of 35 to 40 percent that typically triggers the surgical intervention. The surveillance includes the serial ultrasound and the periodic MAG3 renogram to monitor the drainage and the split function. The prophylactic antibiotics are continued until the obstruction is characterised, and the family is counselled on the signs of the urinary tract infection. [6]

The criteria for the pyeloplasty are the declining split function on the serial MAG3 renograms, the severe or the worsening dilatation, the recurrent urinary tract infection attributable to the obstruction, or the symptomatic presentation. If the split function declines below 35 to 40 percent or the drainage worsens, the pyeloplasty is performed to relieve the obstruction and to preserve the renal function. The long-term prognosis for the unilateral ureteropelvic junction obstruction with the preserved function and the timely intervention is good, with the majority of the children maintaining the normal overall renal function. The surveillance continues into the childhood, and the transition to the adult nephrology care is considered for the child with any residual anomaly. [6]

The family is counselled on the diagnosis, the conservative management, the surveillance plan, and the criteria for the surgery. The reassurance is that the unilateral obstruction with the preserved function has the good prognosis, and that the surveillance is designed to detect any decline in the function early so that the timely surgery can be performed. The long-term chronic kidney disease risk is low for the unilateral anomaly with the normal contralateral kidney, but the surveillance is maintained to confirm the stability. [9]