Introduction: Demographics and comorbid conditions play a role in vascular health, yet their specific impact on cerebrovascular bypass patency remains unclear. Methods: An institutional database of 357 patients with intracranial bypass procedures between 08/2001-05/2022 was retrospectively reviewed. Patients with bypass for all causes (e.g., aneurysm, atherosclerotic disease, Moyamoya disease) were included. Medical history, surgical technique, and flow-related measurements (intraoperatively and on quantitative MRA at follow-up) were compared across biological sex and in relation to bypass patency. Results: Of 357 patients, 141 were male (39.5%) and 216 were female (60.5%) with average age 49.0+/-16.7. Bypass patency at last follow-up was 84.4% for men vs. 69.2% for women (p=0.001). Significant differences were seen in underlying diagnoses, with more aneurysm and Moyamoya cases represented in female sex (p<0.001); irrespective of diagnosis, lower patency rates were seen in women when considering bypass for aneurysm (p=0.032), Moyamoya disease (p=0.035), and for atherosclerotic disease (p=0.159). Medical comorbidities were seen at higher rates in men, with comorbidity score 2.7 vs. 2.1 (p<0.001). Cut flow was higher in men 59.2 vs. 51.1 (p=0.028), but no significant differences were seen in intraoperative bypass flow, cut flow index (CFI), or follow-up QMRA. After removing cases using interposition grafts, similar differences were redemonstrated. Propensity score matched analysis found females have a 2.71 higher chance of bypass occlusion after adjusting for CFI (p=0.017, 95% CI: 1.19-6.18). Conclusion: Biological sex appears to play a significant role in bypass patency, across diagnoses. Women were significantly less likely to have patent bypasses at last follow-up, despite having less medical comorbidities than men and despite having similar intraoperative and perioperative flows. Further study is required to better elucidate the influence of sex on long-term bypass patency.

The authors have declared no competing interest.

Not applicable

No funding received

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

University of Illinois at Chicago, Institutional Review Board, 2003-0457 EC-IC bypass

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

Data may be made available upon appropriate request.