Is a Reassuring MAG-3 Diuretic Renal Scan Really Reassuring?

The mercaptoacetyltriglycine-3 (MAG-3) diuretic renal scan is frequently used to diagnose obstruction in children with hydronephrosis. However, it remains unclear whether a reassuring MAG-3 diuretic scan in the presence of high-grade hydronephrosis accurately predicts the absence of obstruction. We sought to determine if a reassuring nuclear scan can accurately identify patients with high-grade hydronephrosis that can be safely observed.

We retrospectively reviewed the course of 22 children (25 renal units) ages 0-3 months with significant hydronephrosis (Society of Fetal Urology grade 3-4) detected prenatally. All patients underwent a MAG-3 diuretic nuclear renal scan.

Twenty-two patients with 25 renal units were included, 19 with grade 3 and 6 with grade 4 hydronephrosis on ultrasound. Sixteen renal units had a reassuring nuclear scan (T ½ < 10 minutes, average 5.9, range 2-9). Nine renal units had indeterminate scans (T ½ 10-20 minutes, average 12.8, range 10-17). Fifteen of 16 (94%) kidneys with a reassuring nuclear scan had complete resolution of their hydronephrosis. One patient with an initially reassuring nuclear scan underwent pyeloplasty after persistent grade 4 hydronephrosis one year later prompted a repeat MAG-3 indicating obstruction. Eight of 9 (89%) patients with an indeterminate T ½ of 10-20 minutes had complete resolution of their hydronephrosis. One patient was lost to follow up. Average length of follow up and time to resolution was 23.6 months (range 4-61 months).

In pediatric patients with persistent antenatally detected hydronephrosis, a reassuring MAG-3 can allow for safe observation in the vast majority. Only one of 24 renal units with follow-up progressed to obstruction. All patients treated without surgery had complete resolution of their hydronephrosis. Observation with serial ultrasounds may be an appropriate alternative to operative management, even in patients with moderate to severe hydronephrosis in the presence of a reassuring or indeterminate MAG-3 diuretic scan.