Accuracy of measurements used to quantify cranial asymmetry in deformational plagiocephaly

Various measurements are used to quantify cranial asymmetry in deformational plagiocephaly (DP), but studies validating cut-off values and comparing the accuracy of such measurements are lacking. In this study, we compared the accuracy of four different measurements in classifying children with and without DP diagnosed by visual assessment, and sought to determine their optimal cut-off values.

Two experts rated 407 3D craniofacial images of children aged between 3 and 36 months old using the Argenta classification. We then measured the following asymmetry-related variables from the images: Oblique Cranial Length Ratio (OCLR), Diagonal Difference (DD), Posterior Cranial Asymmetry Index (PCAI), and weighted Asymmetry Score (wAS). We created receiver operating characteristic curves to evaluate the accuracy of these variables.

All variables performed well, but OCLR consistently provided the best discrimination in terms of area under the curve values. Subject's age had no clear effect on the cut-off values for OCLR, PCAI, and wAS; however, the cut-off for DD increased monotonically with age. When subjects with discrepant expert ratings were excluded, the optimal cut-off values for DP (Argenta class ≥ 1) across all age-groups were 104.0% for OCLR (83% sensitivity, 97% specificity), 10.5% for PCAI (90% sensitivity, 90% specificity), and 24.5 for wAS (88% sensitivity, 90% specificity).

We recommend using OCLR as the primary measurement, although PCAI and wAS may also be useful in monitoring cranial asymmetry. The threshold of relative asymmetry required for a deformation to appear clinically significant is not affected by the child's age, and DD has no additional utility in monitoring DP compared to using only OCLR.