Sex differences in the human corpus callosum microstructure: a combined T2 myelin-water and diffusion tensor magnetic resonance imaging study.

Sex differences in structure and organization of the corpus callosum (CC) have been identified in healthy adults and may be linked to distinct functional lateralization and processing in men and women. Magnetic resonance imaging (MRI) has facilitated noninvasive assessment of CC sex differences in morphology by volumetric imaging and microstructural organization by diffusion tensor imaging (DTI). Incorporation of recently developed myelin-water fraction (MWF) imaging may improve our understanding of CC sex differences. The aim of the current study was to combine DTI and diffusion tractography with MWF imaging to investigate CC sex differences in 22 healthy adults (11 male, 11 female). We performed MWF imaging using a 5-echo linear combination of spin echo images, and quantified mean diffusivity, axial diffusivity, radial diffusivity and fractional anisotropy (FA) by DTI. Fiber density index (FDi) was quantified using diffusion tractography. The MWF in males was significantly greater than females for the rostral body (p<0.05) and posterior midbody (p<0.005); whereas, the splenium MWF in males was significantly less than females (p<0.05). The DTI analysis revealed significantly increased FA in males compared with females within the genu of the CC (p<0.05). No significant sex-differences existed for mean diffusivity, axial diffusivity, radial diffusivity or FDi. Correlations between DTI parameters and MWF were significant but weak. Results of this study demonstrate regionally dependent sex differences in microstructural composition and organization of the CC and the lack of correlation between DTI and MWF suggest both measures provide unique information within the CC. Copyright (c) 2010 Elsevier B.V. All rights reserved.