Age-Dependent and Sex-Dependent Red Nucleus Morphometry: MRI Evidence With Implications for Neurosurgical Planning

BACKGROUND: The red nucleus (RN) is a midbrain structure involved in motor coordination and cerebellothalamic integration; however, its morphometric variability-particularly with respect to hemispheric laterality and sex-remains poorly characterized. Although age-related changes in cortical and subcortical structures have been extensively studied, normative morphometric data for the RN are limited, despite its relevance to neurosurgical planning and brainstem interventions. METHODS: This retrospective cross-sectional, STROBE-compliant study analyzed high-resolution magnetic resonance imaging (MRI) data from adult patients aged 18 to 90 years who underwent clinically indicated brain MRI at a tertiary referral center. RN morphometric parameters, including bilateral length, width, and distance from the brainstem midline, were measured using standardized protocols. Hemispheric asymmetry and sex-based differences were assessed using paired and independent statistical tests, respectively. Associations with age were evaluated using correlation and regression analyses. Statistical significance was set at P<0.05. RESULTS: A significant hemispheric asymmetry was observed for RN length (RNL), with the left RN consistently larger than the right (P=0.002). No significant laterality was identified for RN width (RNW) or distance from the brainstem midline. Sex-based comparisons demonstrated significantly greater RNW in males than in females (P=0.011), whereas RNL and midline distance did not differ significantly between sexes. Exploratory analyses did not reveal robust associations between age and RN morphometric parameters after complete-case analysis. CONCLUSIONS: This study demonstrates significant hemispheric asymmetry and sexual dimorphism in RN morphometry, providing novel normative anatomic data for a midbrain structure that has received limited attention in prior neuroimaging research. These findings have direct implications for neurosurgical planning and image-guided interventions involving the midbrain, where millimeter-scale anatomic variability may be clinically meaningful. Further multicenter, longitudinal studies are warranted to clarify the role of RN morphometry in neurological aging and neurosurgical outcomes.