Magnetic resonance urography for evaluating outcomes after pediatric pyeloplasty

Purpose: We report the role of magnetic resonance urography in children with ureteropelvic junction obstruction. Differential renal function, the single kidney glomerular filtration rate index, renal transit time, renal length and renal pelvis anteroposterior diameter were compared before and after pyeloplasty. Materials and Methods: Magnetic resonance urography was performed before and after pyeloplasty in 24 patients with a mean age of 1.9 years (range 3 months to 10 years). Renal length, renal transit time and renal pelvis anteroposterior diameter were determined by the radiologist. The volume of functioning renal tissue and descending aorta were segmented and the ratio of the volumes of functioning kidney tissue was used to calculate differential renal function. Rutland-Patlak plots were used to calculate single kidney glomerular filtration rate index, that is the Patlak score. Results: Mean renal pelvis renal pelvis anteroposterior diameter was 3.3 cm. preoperatively and 2.5 cm postoperatively (p = 0.0003). There was no difference in average renal length (p = 0.22). Of the 24 cases 22 (92%) showed stable or improved differential renal function. Improvement in renal transit time was seen in 20 of 23 cases (87%). Of 15 patients with complete Patlak scores 14 (93%) showed postoperative improvement. Mean preoperative and postoperative differential renal function, renal transit time and Patlak score were 36% and 41% (p = 0.003), 16.2 and 8.6 minutes (p = 0.0005), and 6.6 and 11.9 ml per minute (p = 0.01), respectively. Conclusions: Magnetic resonance urography provides superior anatomical and unprecedented functional information to fully define the preoperatively and postoperative status of corrected ureteropelvic junction obstruction. Magnetic resonance urography has the potential to become the imaging study of choice for evaluating pediatric hydronephrosis and obstructive uropathy.