Abstract
Gender identity disorder (GID) is a condition in which sex differs from gender identity. The basic methodology used to diagnose such a disorder involves examination by more than one psychiatrist. It is necessary to develop objective, quantitative criteria for diagnostics in order to improve the credibility of diagnosis, and to aid in decisions as to whether a patient is eligible for sex reassignment surgery. It has long been believed that there are sex-related differences in the shape and size of the corpus callosum (which interconnects the two cerebral hemispheres), and that these differences could form the basis of an objective, quantitative diagnostic technique. Unfortunately, there are, as yet, no established methods. In this study, we used MRI to investigate sex-related differences in the corpus callosum. We described the callosal figures at the midsagittal plane, using Fourier descriptors and central moments to represent the shape. We found that females have stooping corpus callosum relative to males, at a significance level of 10-14. This suggests that sex-related differences in the corpus callosum may consist of differences in the callosal configurations in the cranium, rather than the shape and size of the corpus callosum. Furthermore, using statistical tests (a likelihood ratio test, Kruskal-Wallis test and Mann-Whitney test), we found that most of the GID subjects in our study (MTF, 4; FTM, 11) have a principal orientation of the corpus callosum that is closer to female than male in sex. This means that the callosal principal orientation may qualify as an objective, quantitative criterion for MTF diagnosis.
