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

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.

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.

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.

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.