Assessment of sacral ratio in patients with anorectal malformations: Can magnetic resonance imaging replace conventional radiograph?

Introduction In patients with anorectal malformations (ARM), the sacral ratio (SR) serves as an established predictive marker for functional prognosis and is derived from conventional radiographs. More recently, magnetic resonance imaging (MRI) has emerged as a diagnostic alternative for preoperative/baseline assessment of patients with ARM. With this study we aimed to evaluate if the SR could be reliable be measured from MRI images and if it correlated to SR measurements obtained from radiographs. Methods Two raters analyzed MRI data and conventional radiographs from thirty-one subjects (n = 17 with ARM; n = 14 controls). We calculated intra-class correlation coefficients (ICCs) to test inter-rater reliability and applied paired t-tests to examine if SR parameters from MRI were comparable with those from pelvic radiograph. We further computed Pearson's correlation coefficients to test the linear relationship between SR calculated from MRI and conventional radiographs. Results The ARM and control groups did not statistically differ in their age and weight on the day of the MRI scan. Reliability analysis revealed an excellent inter-rater agreement for SR from radiograph parameters with an intraclass correlation coefficient (ICC) of 0.94, respectively of 0.86 for MRI (frontal plane), and of 0.84 for MRI (sagittal plane). The correlation coefficient between SR calculated from the sagittal MRI and SR calculated from radiograph images was significant and high (r = 0.80, P < 0.001). The SRs from MRI images did not significantly differ from SRs from radiographs, but were also not statistically equivalent. Conclusion Our results demonstrate that the SR can be derived from MRI images with good inter-rater reliability. The SR value is marginal higher when calculated on MRI, presumably due to inclusion of cartilaginous yet unossified structures.