Computed Tomography-Based Evaluation of Positional Cranial Deformities in Emergency Department Patients Aged 15 to 39 Years in Japan.

Positional cranial deformity due to sustained external pressure during infancy frequently improves in early childhood; however, its prevalence in adulthood, particularly in East Asian populations, remains unclear. The authors performed a retrospective cross-sectional analysis of thin-slice cranial computed tomography (CT) images from 242 Japanese individuals aged 15 to 39 years who underwent cranial CT at a single tertiary hospital from 2014 to 2023 and had no intracranial abnormalities. Using the cranial vault asymmetry index (CVAI) and cephalic index (CI), cranial morphology was measured on standardized reconstructed images. The median CVAI was 3.94 (interquartile range, 1.99-6.28); of the participants, 129 (53.3%) met criteria for plagiocephaly, and 46 (19.0%) had moderate-to-severe deformity. Brachycephaly prevalence was 1.6% using Japanese reference-based criteria but 72.3% using international anthropometric-based criteria. Males exhibited a higher CVAI than females; however, no difference in the CVAI and CI was noted by birth year before versus after introducing Japan's Back-to-Sleep campaign. Both indices demonstrated excellent interrater reliability. The observed prevalence of plagiocephaly in this Japanese emergency department CT cohort indicates that plagiocephaly remains common among Japanese young adults, with a significant proportion exhibiting moderate-to-severe deformity, and that infant sleep positioning practices alone do not fully account for its prevalence. The marked discrepancy between Japanese and international criteria suggests that population-specific reference values may be more appropriate for assessing brachycephaly in Japanese adults. This finding is crucial for counseling caregivers and informing treatment decisions for infants with positional cranial deformities.