Uncovering the Role of Risk Factors in Patency of Cerebrovascular Bypass

Introduction: Extracranial-intracranial (EC-IC) bypass has been well described in chronic vaso-occlusive cerebrovascular diseases, such as Moyamoya disease (MMD) and atherosclerotic disease (AD), and in the treatment of complex aneurysms and tumors. In general, demographics and comorbid conditions play a role in vascular health, yet their specific impact on cerebrovascular bypass patency remains unclear. This study examines disease etiology and other modifiable and non-modifiable patient-specific risk factors as potential contributing factors to bypass failure. Methods: An institutional database from the University of Illinois Chicago 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. Data on baseline patient demographics and medical history, surgical technique, and both intraoperative and post-operative flow-related measurements were collected. Comparisons between two steno-occlusive disease states were first performed, followed by comparisons between male and female sexes. Results: In the first analysis, 232 patients met inclusion criteria (AD n=108; MMD n=124). Average age and sex significantly differed between groups (AD 57.2 years, 56.5% male; MMD 36.6 years, 31.5% male, p<0.001). Modified Rankin scale (mRS) at surgery and at follow-up were higher in the AD group, p=0.004 and <0.001, showing a slightly worse baseline functional status, and higher rates of stroke were observed in the AD group by last follow-up (p=0.005). At last follow-up, rates of occlusion did not differ between the AD and MMD groups (25.2% vs. 25.4%, respectively). Of occluded bypasses, the AD group had more bypasses occluded within 1-week compared to MMD (51.9% vs. 34.4%, p=0.176), although not statistically significant. In patients with more than 1-year follow-up and more than 2-year follow-up, MMD tended to have higher rates of occlusion (31.2% vs. 26.1%, p=0.558, and 26.4% vs. 20.7%, p=0.564), though again these differences were not statistically significant. Flow measurements did not differ between AD and MMD, but in subgroup analyses of patients with AD and with MMD, both bypass flow and cut flow index predicted occlusion in both groups. In the second analysis, all 357 patients within the database were considered, with 141 male (39.5%) and 216 female (60.5%) with average age 49.0+/-16.7 years and average follow-up 1.97 years. Bypass patency at last follow-up was 84.4% (n=114) for men vs. 69.2% (n=148) for women (p=0.001). 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), with no differences in intraoperative bypass flow, cut flow index (CFI), or follow-up quantitative magnetic resonance angiography (QMRA). 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: Despite different etiologies for bypass, rates of occlusion at last follow-up did not vary between different steno-occlusive disease groups, although short-term follow-up would suggest earlier bypass failure in AD and extended follow-up trended toward higher occlusion rates in MMD. Additionally, patients with AD were more likely to have further stroke by last follow-up. Importantly, the bypass flow and cut flow index at the time of surgery predicted occlusion in both AD and in MMD. Regarding the influence of sex on bypass patency, women were 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.