Reference Values for Cranial Morphology Based on Three-dimensional Scan Analysis in 1-month-old Healthy Infants in Japan

Currently, molded helmet therapy is used to treat infants with deformational plagiocephaly. However, the indices of normal cranial shape remain unclear, and thus, the prevalence of deformational plagio-cephaly is unknown, particularly in Japan. We investigated the reference values for cranial morpho-logical characteristics in 1-month-old Japanese infants using a three-dimensional scanner, to deter-mine the prevalence of deformational plagiocephaly. One hundred fifty-three healthy infants who vis-ited three hospitals (from April 2020 to March 2021) were enrolled. Cranial shape was measured using a three-dimensional scanner and was analyzed using image analysis software. Outcome measures were cranial volume, length, width, length-width ratio, circumference, asymmetry, and vault asymmetry in-dex; cephalic index; and anterior, posterior, and overall symmetry ratios. The cranial vault asymmetry index >3.5% or >_10% were diagnosed as deformational or severe deformational plagiocephaly, respec-tively. The mean age at measurement was 35.7 days. The mean cranial volume was 559 mL; cranial length, 129 mm; cranial width, 110 mm; length-width ratio, 118%; cephalic index, 85.2%; cranial cir-cumference, 377 mm, cranial asymmetry, 6.4 mm; cranial vault asymmetry index, 5.0%; and anterior, posterior, and overall asymmetry ratios, 93.1%, 91.3%, and 96.4%, respectively. The prevalence of defor-mational and severe deformational plagiocephaly was 64.7% and 6.6%, respectively. Sex-based differ-ences were observed for cranial volume and width. The results obtained in this study can be consid-ered standard values that can facilitate the differentiation of abnormal infant cranial morphological characteristics for Japanese medical practitioners.