Voiding cystourethrography and 99MTC-MAG3 renal scintigraphy in pediatric vesicoureteral reflux: what is the role of indirect cystography?

Background: Primary vesicoureteral reflux (VUR) is the most common urological anomaly in children. Voiding cystourethrography (VCUG) is considered the reference standard for the diagnosis of VUR. Even if it is a secure and standardized technique, it is still an invasive method, hence, the effort to find an alternative method to diagnose VUR. The aim of the study is to evaluate the diagnostic accuracy of 99mTC-MAG3 scintigraphy with indirect cystography in detecting VUR and to estimate any interobserver variability in 99mTC-MAG3 scintigraphy interpretation. Methods: The authors retrospectively reviewed all the pediatric patients who underwent both a VCUG and a 99mTC-MAG3 renal scintigraphy at the study institution between 2012 and 2016. Results: A total of 86 children (and 168 renal units) were included. MAG3 scan revealed a sensitivity of 54% and a specificity of 90% with positive predictive value of 79% and negative predictive value of 73%. Each MAG3 scintigraphy was then independently and blindly evaluated by a pediatric urologist and two nuclear physicians. After revision, the concordance between VCUG and MAG3 in reflux cases dropped from 54% to 27% (on average), and the reviewers reclassified most examinations as non-conclusive. Conclusions: 99mTC-MAG3 renal scintigraphy with indirect cystography showed low sensitivity in detecting VUR of any grade and cannot, therefore, be proposed as completely alternative to VCUG in the diagnosis of VUR. Moreover, MAG3 scintigraphy interpretation for the diagnosis of VUR has a very high interobserver variability, mostly because of the lack of a correct and complete voiding phase. [Table presented]