To date, research findings are inconsistent about whether neuroanatomy in transgender persons resembles that of their natal sex or their gender identity. Moreover, few studies have examined the effects of long-term, cross-sex hormonal treatment on neuroanatomy in this cohort. The purpose of the present study was to examine neuroanatomical differences in transgender persons after prolonged cross-sex hormone therapy.
Eighteen transgender men (female-to-male), 17 transgender women (male-to-female), 30 non-transgender men (natal men), and 27 non-transgender women (natal women) completed a high-resolution structural MRI scan at 3Tesla. Eligibility criteria for transgender persons were gender affirming surgery and at least 2 years of cross-sex hormone therapy. Exclusion criteria for non-transgender persons were presence of psychiatric or neurological disorder.
Mean neuroanatomical volume for the amygdala, putamen and corpus callosum differed between transgender women and natal women but not between transgender women and natal men. Differences between transgender men and natal men were found in several brain structures, including the medial temporal lobe structures and cerebellum. Differences between transgender men and natal women were found in the medial temporal lobe, nucleus accumbens, and 3rd ventricle. Sexual dimorphism between non-transgender men and women included larger cerebellar volumes and smaller anterior corpus callosum in natal men relative to natal women. The results remained stable after correcting for additional factors including age, total intracranial volume, anxiety, and depressive symptoms.
Neuroanatomical differences were region-specific between transgender persons and their natal sex as well as their gender identity suggesting localized influence of sex hormones on neuroanatomy.