120 The Impact of Cerebrovascular Steno-Occlusive Disease Subtype on Surgical and Clinical Outcomes After Direct STA-MCA Bypass Surgery

INTRODUCTION: While well-established in Moyamoya Disease (MMD), the role of direct superficial temporal artery (STA) to middle cerebral artery (MCA) bypass in non-Moyamoya (N-MMD) steno-occlusive syndromes remains controversial. Nonetheless, the recurrent stroke risk in N-MMD patients remains high despite best medical management. METHODS: Single-center retrospective review of direct STA-MCA bypass cases from 2014–2023 was performed. Cases were excluded if they involved double-barrel bypass, interposition grafts, or if the surgical indication was not cerebral hypoperfusion. Direct bypass graft patency was serially assessed on follow-up imaging. RESULTS: Of the 139 included cases, 88 (63.3%) were MMD and 51 (36.7%) were N-MMD cases. Mean age was 49.2 years with a mean follow-up of 18.5 months. The overall postoperative ipsilateral hemispheric stroke rate was 11.5%. The 30-day perioperative stroke rate was 6.5% with no difference between MMD (5.7%) and N-MMD (7.8%) cases (p=0.725). Despite 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) and ipsilateral ischemic stroke (15.7% N-MMD vs. 9.1% MMD, p=0.276) to MMD cases. Higher preoperative total hemispheric flow on Non-invasive Optimal Vessel Analysis (NOVA) imaging was the only variable associated with prolonged direct bypass graft patency (HR 0.39, p=0.036*). Postoperative stroke-free survival improved if dural synangiosis was performed (HR 0.31, p=0.033*). In multivariate analysis, direct bypass graft occlusion (HR 4.58, p=0.009*) and a preoperative DWI-ASPECTS <8 (HR 3.90, p=0.024*) predicted reduced stroke-free survival. CONCLUSIONS: This robust cohort of MMD and N-MMD STA-MCA bypass cases highlights the efficacy of a technically sound direct bypass across all subtypes of steno-occlusive disease. Preoperative assessment of hemispheric flow on NOVA imaging may improve surgical risk stratification. Further examination of the benefits of adjunctive dural synangiosis, especially for N-MMD patients, remains warranted.