# Diagnostic utility of magnetic resonance urography in pediatric ureteropelvic junction obstruction: evaluating changes in anteroposterior diameter of the renal pelvis following furosemide administration

## TL;DR

This study evaluates how MRU with furosemide can help diagnose kidney blockages in children by measuring changes in kidney shape.

## Contribution

The study identifies a 6 mm increase in renal pelvis diameter as a potential diagnostic cutoff for ureteropelvic junction obstruction in children.

## Key findings

- An increase in renal pelvis diameter greater than 6 mm after furosemide injection is a potential diagnostic criterion for obstruction.
- The increase was significantly greater on the obstructed side compared to the healthy side.
- MRI reliably detects crossing vessels associated with obstruction.

## Abstract

Magnetic resonance urography (MRU) with diuretic injection is increasingly used to evaluate pediatric ureteropelvic junction obstruction, providing anatomical and functional information without ionizing radiation.

To analyze the increase in anteroposterior diameter of the renal pelvis following furosemide injection during MRU to determine a diagnostic cutoff. To assess whether this increase supports etiological diagnosis and whether magnetic resonance imaging (MRI) reliably detects crossing vessels.

We retrospectively included all children who underwent surgery for ureteropelvic junction obstruction at our institution between January 2010 and January 2023 and had preoperative MRU. For each patient, the increase in renal pelvis diameter after furosemide injection during MRU was measured on the obstructed and contralateral healthy sides. Measurements were compared to determine a pathological cutoff. The change in renal pelvis diameter was also compared according to etiology (intrinsic vs. extrinsic). The association between crossing vessels identified on MRI and intraoperative findings was also assessed.

Seventy patients (median age 9) were included. The increase in renal pelvis diameter was significantly greater on the obstructed side compared to the contralateral side (P < 0.001). The optimal cutoff for predicting obstruction was 6 mm (sensitivity 68.6%, specificity 87.1%). No significant difference was found in the change in renal pelvis diameter according to etiology (P = 0.86). The association between crossing vessels identified on MRI and during surgery was significant (P < 0.001).

An increase greater than 6 mm in renal pelvis diameter after furosemide injection during MRU could represent an additional diagnostic criterion for pediatric ureteropelvic junction obstruction.