Age-related patterns and strong correlation between cranial and ear asymmetry in healthy children: a CT-based cross-sectional study

PURPOSE: Severe cranial deformity has been thought to cause secondary ear misalignment; however, the developmental patterns of cranial and ear asymmetry have not been systematically characterized. We aimed to clarify age-related variations and the interrelationship of cranial and ear asymmetry in healthy Japanese children using head computed tomography (CT). METHODS: We retrospectively analyzed CT data from children imaged for minor head trauma between 2006 and 2023. Cranial asymmetry was assessed using the cranial vault asymmetry index (CVAI), and ear asymmetry was quantified by the absolute ear shift angle (ESA) derived from the alignment of the external auditory canals. Both indices were categorized into five grades, with grade ≥ 3 considered moderate to severe. Age-related trends were evaluated using regression and random-forest models with partial dependence plots (PDPs). RESULTS: A total of 235 children were included (138 males and 97 females; median age, 12 months). CVAI and absolute ESA showed a significant positive correlation (r = 0.58, p < 0.001). The proportion of grade ≥ 3 deformity declined with age: CVAI peaked at 50% at 4-5 months and decreased to 29% after 5 years, whereas ESA peaked at 56% at 1 month and decreased to 24% after 5 years. PDPs indicated that absolute ESA decreased mainly within the first 6 months, while CVAI showed a more marked decline after 3 years. CONCLUSION: Both CVAI and ESA decreased in severity with age and showed a strong positive correlation, suggesting coordinated cranial and ear morphological development. The temporal patterns of improvement differed between the two measures.