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Value of Supranormal Function and Renogram Patterns on ^99mTc-Mercaptoacetyltriglycine Scintigraphy in Relation to the Extent of Hydronephrosis for Predicting Ureteropelvic Junction Obstruction in the Newborn

¹ Department of Nuclear Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
² Department of Pediatrics, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
³ Department of Urology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
⁴ Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
⁵ Department of Information and Statistics, Daejeon University, Daejeon, Korea

We investigated the value of supranormal function and renogram patterns on ^99mTc-mercaptoacetyltriglycine (^99mTc-MAG3) scintigraphy in relation to the extent of hydronephrosis for predicting ureteropelvic junction (UPJ) obstruction in the newborn. Methods: We studied 48 patients with prenatally diagnosed unilateral hydronephrosis that was confirmed on postnatal ultrasonography. The anteroposterior pelvic diameter (APPD) and the Society for Fetal Urology (SFU) grade were measured on 1-mo ultrasonography to assess the extent of hydronephrosis. Neonates with an APPD of 10 mm or a differential renal function of 40% were excluded. Supranormal function (55%) and renogram grades (1, not obstructive; 2, indeterminate; 3, obstructive; and 4, prolonged parenchymal transit) were determined on 1-mo ^99mTc-MAG3 renography. Multivariate logistic regression analysis was performed to predict the presence of obstruction. Results: Of the 48 kidneys with hydronephrosis, 19 were diagnosed as having UPJ obstruction. Twenty-nine kidneys were classified as having nonobstructive hydronephrosis. The APPD of the 19 kidneys with obstruction (24.3 ± 9.2 mm) was significantly larger than that of the 29 kidneys without obstruction (17.5 ± 11.2 mm; P < 0.05). The SFU grades of UPJ obstruction (2 with grade 3, 17 with grade 4) were also significantly higher than those without UPJ obstruction (grades 1–4 in 1, 6, 10, and 12 kidneys, respectively; P < 0.01). Supranormal function was present in 4 kidneys with UPJ obstruction but in none without obstruction (P < 0.001). ^99mTc-MAG3 renography of the 19 obstructions showed grades 2, 3, and 4 renograms in 4, 8, and 7 patients, respectively. The 29 without obstruction revealed significantly lower grades (grades 1–4 in 10, 13, 5, and 1 patient, respectively; P < 0.001). Multivariate logistic regression analysis revealed that the addition of supranormal function or renogram grade in the model significantly increased the likelihood ratio in comparison with that of the SFU grade only (² = 7.73 and 9.99, respectively; P < 0.01). Of the 29 neonates with SFU grade 4, supranormal function or renogram grade 4 had a positive predictive value of 90% (9/10). Conclusion: ^99mTc-MAG3 renography at 1 mo after birth has a significant additive value in relation to the degree of hydronephrosis in predicting UPJ obstruction in patients with prenatally diagnosed unilateral hydronephrosis with normal function.

Key Words: ^99mTc-mercaptoacetyltriglycine renography • ureteropelvic junction obstruction • neonates • supranormal function