OR31-03 Testosterone Gender-affirming Hormonal Therapy Is Associated With Decreased Cerebral Blood Flow In Transgender Teens

Disclosure: S. Cote: None. K. Fathy: None. S. Lenet: None. O. Espinosa-Bentancourt: None. E. Lavallee: None. E. Croteau: None. D. Rottembourg: None. J. Lepage: None. K. Whittingstall: None. There is increasing demand for gender-affirming hormonal therapy (GAHT) in recent years, with increased access to GAHT for transgender teenagers. While it is well documented that psychological outcomes and quality of life improve after GAHT, it remains unclear how cerebrovascular physiology changes with GAHT. Therefore, this study aimed to investigate the effects of testosterone GAHT on cerebral microvascular and macrovascular physiology in teenage transgender men receiving GAHT. Six teenage transgender men were referred by their endocrinologist prior to the start of GAHT. Participants visited the research center before GAHT (session 1) and between 3 to 9 months into their GHAT (session 2). At each visit, participants completed a non-contrast-enhanced magnetic resonance imaging (MRI) protocol. This protocol assessed the macrovasculature using time-of-flight magnetic resonance angiography to visualize cerebral arteries and estimate diameters of the Circle of Willis and 2D-Phase Contrast to estimate large artery blood velocity. The microvasculature was assessed using pseudo-Continuous Arterial Spin Labelling, which estimates cerebral blood flow (CBF). Paired-sample t-tests were performed between sessions to determine if arterial diameters, CBF and blood velocity change with GAHT. Whole-brain CBF significantly decreased with GAHT between session 1 and session 2 (CBF(S1)=69.15 +/- 5.85 ml/100g/min; CBF(S2)=59.30 +/- 8.11 ml/100g/min; t=3.19, p=0.02, df=5). The average percent change in CBF was -9.85%, and the largest decrease experienced by a participant was -20.44%. Note that even though CBF decreased, average whole-brain CBF for all participants remained in a healthy range. We observed no significant change in large artery blood velocity or arterial lumen diameters of the Circle of Willis after starting GAHT. Our results suggest that GAHT influences the brain’s microvasculature. As women tend to have higher CBF than men, the reduction in CBF likely reflects a masculinization of the brain with GAHT. Without EEG to probe neuronal activity, it is difficult to determine if the change is due to decreased neuronal activity or a structural and/or functional change in the microvasculature. Considering that little is known about the long-term effects of GAHT on the brain, these results highlight the need to better understand how hormonal states impact human cerebrovascular physiology and how it may relate to risk for cerebrovascular disease and neurological disorders. Presentation: Sunday, June 18, 2023