Background and purpose: Determinants of successful recanalization likely differ for Merci thrombectomy and intra-arterial pharmacological fibrinolysis interventions. Although the amount of thrombotic material to be digested is an important consideration for chemical lysis, mechanical debulking may be more greatly influenced by other target lesion characteristics.
Methods: In consecutive patients with acute ischemic stroke treated with Merci thrombectomy for middle cerebral artery M1 occlusions, we analyzed the influence on recanalization success and clinical outcome of target thrombus size (length) and shape (curvature and branching) on pretreatment T2* gradient echo MRI.
Results: Among 65 patients, pretreatment MRI showed susceptibility vessel signs in 45 (69%). Thrombus length averaged 13.03 mm (range, 5.56-34.91) and irregular shape (curvature or branching) was present in 17 of 45 (38%). Presence and length of susceptibility vessel signs did not predict recanalization or good clinical outcome. Substantial recanalization (Thrombolysis In Cerebral Infarction 2b or 3) and good clinical outcome (modified Rankin Scale score ≤2) were more frequent with regular than irregular susceptibility vessel signs shape (57% versus 18%, P=0.013; 39% versus 6%, P=0.017). On multiple regression analysis, the only independent predictor of substantial recanalization was irregular susceptibility vessel signs (OR, 0.16; 95% CI, 0.04-0.69; P=0.014); and leading predictors of good clinical outcome were baseline National Institutes of Health Stroke Scale (OR, 1.20; 95% CI, 1.03-1.40; P= 0.019) and irregular susceptibility vessel signs (OR, 9.36; 95% CI, 0.98-89.4; P=0.052).
Conclusions: Extension of thrombus into middle cerebral artery division branches and curving shape of the middle cerebral artery stem, but not thrombus length, decrease technical and clinical success of Merci thrombectomy in M1 occlusions.