To quantify magnetic resonance imaging (MRI) findings of congenital muscular torticollis (CMT) and to demonstrate the usefulness of quantitative MRI findings in the management of CMT.

This was a retrospective study of 160 subjects with CMT who had undergone neck MRI at the age of 48 months or younger at a tertiary medical center. Among the 160 subjects, 54 had undergone surgical release of CMT and 106 subjects had not undergone surgery. For the quantitative analysis, the ratios of area and intensity of the MRI findings were measured and compared between the two groups (ratio of area = the largest cross-sectional area of the SCM with CMT - the cross-sectional area of the contralateral SCM without CMT / the cross-sectional area of the contralateral SCM without CMT; ratio of intensity = the mean gray color intensity of the contralateral SCM without CMT - the lowest mean gray color intensity of the SCM with CMT / the mean gray color intensity of the contralateral SCM without CMT). Receiver operating characteristic (ROC) curve analysis was conducted for the ratios of area and intensity in order to find the optimal cutoff value for determining the need for surgery in CMT cases.

The ratios of area and intensity were significantly higher in the surgical group than in the non-surgical group (p≤0.001), suggesting that the sternocleidomastoid muscle (SCM) was thicker and darker in the surgical group than in the non-surgical group. The optimal cutoff value for the ratio of area was 0.17 and that for the ratio of intensity was 0.05. All subjects with a ratio of intensity less than 0.03 belonged to the non-surgical group, and all subjects with a ratio of intensity greater than 0.16 were categorized in the surgical group.

The quantitative MRI findings, i.e., ratios of area and intensity, may provide a guideline for deciding the need for surgical intervention in CMT patients. Further prospective studies are required to verify these findings.