Sexual dimorphism in the human corpus callosum? A comparison of methodologies.

Mid-sagittal magnetic resonance images of 104 normal individuals were analyzed to assess whether or not the corpus callosum or parts thereof is sexually dimorphic in favor of females. Subjects were 56 males and 48 females, both groups being closely age matched. The outline of the corpus callosum was divided into seven subareas, using three different orientations. A comparison was made between subareas with the divisions based on different orientations. Results showed significant differences (P < 0.05) in all cases, with one exception in females. No significant sexual dimorphism was found, with the exception of one subarea in one of the orientations which was significantly larger in males. No significant correlation was found between corpus callosal area and either cerebral hemispheric area or an estimate of cranial capacity. Relative measures, incorporating these two brain size indicators as covariates, also showed no significant sexual dimorphism. In conclusion, no sexual dimorphism of the human corpus callosum favoring females was found in this study, and it appears that inadequate sampling, differing feature orientation, and inappropriate size correction procedures may have been factors responsible for conflicting results in previous studies.