Non-contrast-enhanced magnetic resonance angiography for detecting crossing renal vessels in infants and young children: comparison with contrast-enhanced angiography and surgical findings

Background: Knowing that ureteropelvic junction obstruction is due to a crossing renal vessel is essential in choosing the appropriate surgical treatment. Objective: To evaluate the diagnostic accuracy of non-contrast magnetic resonance (MR) angiography in identifying crossing renal vessels in children younger than 4 years old with unilateral hydronephrosis. Materials and methods: A retrospective review of preoperative MR urography of children with unilateral hydronephrosis was conducted by two independent readers. The presence or absence of crossing renal vessels was identified and compared with surgical findings. Results: Twenty-nine patients were included. The disagreement between MR angiography with and without contrast enhancement in detecting a crossing renal vessel was 8%. The disagreement between non-contrast-enhanced MR and surgical findings was 17%. The disagreement between contrast-enhanced MR angiography and surgical findings was 25%. The balanced triggered angiography without contrast enhancement had a sensitivity of 70% (95% confidence interval [CI]: 35-93%) and a specificity of 93% (95% CI: 66-100%). Contrast-enhanced MR angiography had a sensitivity of 56% (95% CI: 21-86%) and a specificity of 91%. (95% CI: 59-100%). Conclusion: MR without contrast enhancement may be a reliable, valid and safe alternative to contrast-enhanced MR angiography for identifying crossing renal vessels.