Midsagittal Morphometry of the Corpus Callosum in Native Tibetan Adults: Distinctive Preservation of the Splenium and Anterior Sexual Dimorphism

Background: To establish normative midsagittal corpus callosum (CC) morphometric data in healthy native Tibetan adults and to examine sex- and age-related differences after adjustment for brain size. Methods: High-resolution T1-weighted MRI was acquired in 156 native Tibetan adults (70 men, 86 women; age 18–66 y, mean 35.2±12.7 y) living permanently above 3500 m. In total, 7 subregional CC areas (Witelson scheme) were manually measured on midsagittal slices and normalized to the midsagittal intracranial area. Results: After brain-size adjustment, total CC area showed no sex difference. Men exhibited a significantly larger rostrum (W1; P =0.016). Contrary to typical age-related atrophy in lowland populations, splenial area (W7) showed robust positive associations with age in both men (ρ=0.382, P =0.001) and women (ρ=0.241, P =0.025); rostral area increased with age in men only (ρ=0.261, P =0.029). Conclusions: Native Tibetan adults display a unique CC profile with localized anterior sexual dimorphism and age-associated posterior preservation. These findings likely reflect neuroplastic adaptations to lifelong hypobaric hypoxia and provide essential population-specific reference values to prevent misinterpretation of adaptive morphology as pathology in neurosurgical and craniofacial practice at high altitude.