Surgical validation of functional magnetic resonance urography in the study of ureteral anomalies distal to the uretero-pelvic junction in a pediatric cohort.

Background: Ureteral anomalies distal to the uretero-pelvic junction (UPJ) belong to the wide spectrum of congenital anomalies of the kidney and urinary tract (CAKUT). They can cause severe obstruction requiring a detailed anatomical depiction to define the surgical approach. Up to date, ultrasonography, voiding cystourethrography and scintigraphy are considered the gold-standard diagnostic tools to study obstructive anomalies of the urinary tract; however, they do not provide accurate ureteral anatomical details. The aim of our study was to evaluate the concordance between functional magnetic resonance urography (fMRU) and intraoperative findings to define ureteral anomalies distal to UPJ.

Methods: Pediatric patients with ureteral anomalies distal to the UPJ who underwent surgery after performing fMRU were retrospectively collected. Surgical data were compared with radiological results. The concordance was assessed considering both pathological and non-pathological urinary tracts and was calculated by means of the Cohen's kappa coefficient. fMRU diagnostic accuracy was defined by sensitivity, specificity, and binomial exact confidence intervals.

Results: We included 46 patients. The sensitivity and specificity of fMRU were 98.0% and 83.3%; positive predictive value 90.4%, negative predictive value 96.2%. The concordance between surgical findings and fMRU was 92.3%, with a Cohen's k coefficient of 0.83 (excellent).

Conclusions: Our study demonstrates the excellent agreement between fMRU and surgical findings in the definition of ureteral anomalies distal to the UPJ in children. Thus, it could be considered a valid imaging technique in the preoperative planning as it provides the surgeon with important information regarding the etiology and site of the obstruction.