加齢に伴う側頭筋および咬筋の縦断的定量化：10年間のCT研究

Age-related temporalis and masseter atrophy contributes to facial aging and may reflect systemic sarcopenia. However, longitudinal data quantifying this decline in healthy individuals are lacking, as prior research is limited to cross-sectional analyses or short-term follow-up. This study provides the first extended, longitudinal CT-based quantification of masticatory muscle atrophy in healthy adults over a multi-year period.

This retrospective study analyzed serial head CT scans from 93 healthy adults (48 men, 45 women; mean initial age, 33.2 years) over a mean follow-up of 10.3 years. Two independent raters measured standardized temporalis and masseter thickness and whole-muscle volume. Absolute, percent, and annualized changes were calculated and correlated with time and age.

Both muscles showed significant, progressive decline. Temporalis thickness decreased by 1.57 mm (≈24.8%; ~0.15 mm/year) and masseter thickness by 1.20 mm (≈10.0%; ~0.12 mm/year). Volumetrically, temporalis declined from ~20.1 to ~16.3 cm³ (mean loss ~3.8 cm³; ≈20%; ~0.28 cm³/year) and masseter from ~17.6 to ~16.1 cm³ (mean loss ~1.5 cm³; ≈8-10%; ~0.12 cm³/year). Declines in both thickness and volume correlated with longer follow-up and older age at final scan, with larger and more variable losses in the temporalis.

This study provides novel longitudinal evidence that the temporalis and masseter muscles undergo measurable atrophy in adulthood. Volumetric reductions corroborated thickness losses and revealed the temporalis as particularly vulnerable. These changes help explain aesthetic features such as temporal hollowing and jawline descent, underscoring the contribution of muscle loss to facial aging and motivating further investigation into preventive or restorative approaches.