Detailed Analysis of Thrombus Composition and Endovascular Thrombectomy Efficiency in Ischemic Stroke Patients with Middle Cerebral Artery Occlusion Undergoing Thrombectomy

<b>Introduction:</b> We aimed to clarify the influence of the thrombus composition on ischemic stroke endovascular thrombectomy (EVT) efficiency by utilizing various staining methods for patients that presented with occlusions of the middle cerebral artery (MCA). <b>Methods:</b> Between September 2017 and May 2021, we analyzed thrombi retrieved during endovascular thrombectomy EVT in patients with acute ischemic stroke due to middle cerebral artery (MCA) occlusion. Patients with reperfusion failure, intracranial atherosclerotic occlusions, and inadequate staining were excluded. The thrombus composition was stratified using three staining techniques-Hematoxylin and Eosin (H&E), Martius Scarlet Blue (MSB) staining, and immunohistochemistry (IHC) for red blood cells (RBCs), white blood cells (WBCs), fibrin (Fibrin II), and platelets (CD41). Associations between EVT efficiency outcomes and the thrombus composition were evaluated. <b>Results:</b> During the study period, thrombus was available for analysis in 159 patients. A total of 59 patients were included in the main analysis. Increases in the trichotomized RBS tertiles were associated with decreases in the components of various platelet/other components but not for fibrin. A modified first pass effect (mFPE) of the modified Thrombolysis in Cerebral Infarction perfusion scale (mTICI) 2b or higher was associated with larger thrombus surface area (16.0 ± 11.6 vs. 47.4 ± 62.3 mm², <i>p</i> = 0.005), a higher MSB fibrin content (29.8 ± 10.7 vs. 21.3 ± 10.9%, <i>p</i> = 0.002), and IHC fibrin (28.5 ± 14.5 vs. 20.1 ± 11.4%, <i>p</i> = 0.008). There was a marginal association between the mTICI 2b mFPE and lower MSB platelet/other components (27.6 ± 20.9 vs. 34.4 ± 14.9%, <i>p</i> = 0.078). The discrepancy between MSB platelet/others and IHC platelets was greater in the mFPE (-) group, suggesting that components other than platelets may contribute to EVT resistance. A mFPE of mTICI 2c or higher was associated with greater thrombus surface area (17.8 ± 11.9 vs. 37.7 ± 55.0 mm², <i>p</i> = 0.015) and MSB fibrin (32.1 ± 10.3 vs. 22.8 ± 11.0%, <i>p</i> = 0.002). There was a marginal reverse association between the mTICI 2c mFPE and MSB RBCs (33.4 ± 20.2% vs. 41.5 ± 17.3%, <i>p</i> = 0.062). There was no significant association between final near-complete reperfusion and the thrombus composition. <b>Conclusions:</b> In patients presenting with occlusions of the MCA, a higher thrombus fibrin content is associated with better EVT efficiency. Both a higher MSB platelet/other components and RBC content may have a negative influence on EVT efficiency. These results may help identify preprocedural biomarkers beyond the conventional assessment of RBCs, WBCs, and fibrin compositions, which could guide decision-making during mechanical thrombectomy.