Abstract 199: Non‐Dominant M2 Vessel Found To Be Co‐Dominant Post‐Recanalization

Introduction/Purpose The benefit of mechanical thrombectomy (MT) in medium vessel occlusion (MeVO) is not well‐defined, with ESCAPE‐MeVO, DISTAL, and DISCOUNT trials demonstrating that patients who received MT had similar 90‐day functional outcomes and higher rates of symptomatic intracranial hemorrhage as compared to those who were medically managed. However, the results of these trials are confounded by the variable definition of occlusion location considered to be MeVO, high rates of thrombolytics used in both treatment arms of all three trials, and crossover between arms. Existing observational data support thrombectomy in dominant or proximal M2 occlusions, but how should a case with a non‐dominant appearing M2 occlusion be approached? We answer this question with a unique case from our institution. Methods A case report from a comprehensive stroke center is presented. Results A male in his 70s with past medical history of hypertension, congestive heart failure, chronic kidney disease, former smoking, and recent bowel obstruction surgery presented to an outside facility for confusion and right middle cerebral artery (MCA) syndrome with NIHSS of 17, improving to 7 upon transfer to our facility. Initial non‐contrast CT head demonstrated no ischemic changes, CT angiography confirmed occlusion of a small‐caliber, distal superior M2 vessel, and CT perfusion demonstrated no core infarct with 69 cc of ischemic penumbra (Tmax>6 seconds). While the occlusion was distal and in a non‐dominant appearing vessel, mechanical thrombectomy was pursued given the size of tissue at risk. On initial angiography, the M2 vessel was confirmed to be diminutive in caliber with distal occlusion seen. However, after complete recanalization with one pass of direct aspiration (TICI 3), the vessel was much larger in caliber (Figure 1). MRI brain afterwards demonstrated a minor infarct in the right corona radiata and frontal operculum, transcranial doppler demonstrated no evidence of vasospasm, and the patient was discharged with minor pyramidal weakness of the right arm and leg, scoring 0 on NIHSS. Conclusions This patient case demonstrates how thrombectomy of M2 occlusions should be approached on a case‐by‐case basis, utilizing patient examination and mismatch volume on perfusion imaging to guide decision making. In this case, an occluded co‐dominant vessel appeared as non‐dominant on initial angiography, though penumbra burden was large based on both initial clinical exam and radiographic mismatch. We conjecture that this vessel was disguised as non‐dominant pre‐thrombectomy due to stagnation of contrast flow pre‐recanalization and hyperperfusion post‐thrombectomy. image