The impact of cerebrovascular steno-occlusive disease subtype on surgical and clinical outcomes after direct STA-MCA bypass surgery

OBJECTIVE Although well-established in moyamoya disease (MMD), the role of direct superficial temporal artery (STA) to middle cerebral artery (MCA) bypass in non-MMD (N-MMD) cerebrovascular steno-occlusive syndromes remains controversial. Nonetheless, the recurrent stroke risk in patients with N-MMD, despite best medical management, remains exceedingly high—especially for those suffering from hypoperfusion-related ischemia. The study objective was to determine the relative safety and efficacy profiles of direct STA-MCA bypass surgery for MMD and N-MMD patients in a large contemporary cohort. METHODS The authors conducted a retrospective review of all direct STA-MCA bypass cases performed between 2014 and 2023 at a high-volume center, which yielded 139 cases. Cases were excluded if they involved double-barrel bypass, an interposition graft, or if the surgical indication was not cerebral hypoperfusion. Direct bypass graft patency was serially assessed on follow-up vessel imaging. RESULTS Of the 139 included cases, 88 (63.3%) were MMD and 51 (36.7%) were N-MMD cases. The mean patient age was 49.2 years and 60.4% were female. The mean follow-up duration was 18.5 months. The perioperative stroke risk within 30 days of revascularization was 6.5% for the overall cohort, with no significant difference (p = 0.725) observed between MMD (5.7%) and N-MMD (7.8%) cases. The overall postoperative ipsilateral hemispheric and MCA distribution stroke rates at last follow-up were 11.5% and 9.4%, respectively. Despite a greater medical comorbidity burden, N-MMD cases demonstrated comparable rates of direct bypass graft occlusion (21.6% N-MMD vs 28.4% MMD, p = 0.426), MCA-distribution ischemic stroke (11.8% N-MMD vs 7.9% MMD, p = 0.549), and ipsilateral ischemic stroke (15.7% N-MMD vs 9.1% MMD, p = 0.276) to patients with MMD at last follow-up. Higher preoperative total hemispheric flow on noninvasive optimal vessel analysis (NOVA) imaging was the only variable associated with prolonged direct bypass graft patency (hazard ratio [HR] 0.39, p = 0.036). Postoperative stroke-free survival was improved by performing dural synangiosis (HR 0.31, p = 0.033) and, in multivariate analysis, was reduced with direct bypass graft occlusion (HR 4.58, p = 0.009) and a preoperative diffusion-weighted imaging–Alberta Stroke Program Early CT Score (DWI-ASPECTS) < 8 (HR 3.90, p = 0.024). CONCLUSIONS This robust cohort of MMD and N-MMD STA-MCA bypass cases highlights the safety and efficacy of a technically sound direct bypass across all subtypes of cerebrovascular steno-occlusive disease. Careful attention to preoperative MRI parameters, including hemispheric flow rates on NOVA imaging, may improve surgical risk stratification. Further examination of the benefits of adjunctive indirect bypass or dural synangiosis, especially for patients with N-MMD, remains warranted.