By PD Dr. Peter Sporns1,2 and PD Dr. Ilko Maier3

1Department of Diagnostic & Interventional Neuroradiology, University of Basel, Basel, Switzerland

2 Department of Diagnostic & Interventional Neuroradiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

3Department of Neurology, University Medicine Göttingen, Göttingen, Germany


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The role of mechanical thrombectomy in medium vessel occlusions

Mechanical Thrombectomy has become standard of care for patients with large vessel occlusion (LVO) strokes in the anterior circulation after the publication of the first five mechanical thrombectomy (MT) landmark studies (1) (2) (3) (4) (5). However, the proportion of patients with more distal, medium vessel occlusions (MeVO) of the middle cerebral artery (M2 segment of the MCA) was low (8%) and only the MR CLEAN study included such patients (1). In a subgroup analysis of the meta-analysis of the first five MT landmark studies, the effect of MCA M2 thrombectomies was no longer statistically significant (6). Concerning the strong effect on functional outcome, however, MT of MCA M2 and M3 occlusions are recommended by the 2018 American Heart Association/American Stroke Association guidelines, however, with a weak recommendation (7). In addition, only little evidence exists concerning MeVOs of the P2/3 segments of the posterior cerebral artery (PCA) and A2/3 segments of the anterior cerebral artery (ACA) (8).

Despite the lack of evidence from randomized, controlled trials, MT of MeVOs of the anterior and posterior circulation are being performed in most large thrombectomy centers. This development is not only driven by the increasing experience in general, but also technical and procedural innovations, especially concerning the use of stent retriever of smaller sizes (micro stent retrievers) (9) (10) (11) (12). In this respect, multiple, retrospective studies already provided evidence of feasibility and safety of MTs of MeVOs (13) (14) (8) (15). The analysis of two large, prospectively maintained MT databases also revealed similar recanalization rates and safety profiles concerning intracerebral hemorrhages, mortality or procedure-related complications compared to LVOs (16) (17).

The optimal treatment strategy for distal cerebral vessel occlusions to date is unknown. Especially the role of sole systemic thrombolysis, bridging thrombolysis or i.a. thrombolysis in combination or compared to MT alone is not known. In this context, recanalization rates after IVT have been shown to be higher in MeVOs compared to LVOs (successful recanalization have been found in 43% of M3 MCA, ACA, or PCA-, in 37% of M2 MCA-, in 22% in M1 MCA and only in 11% of ICA occlusions) (18). In the above-mentioned retrospective studies, fast and successful recanalization was an independent predictor for functional outcome in MeVOs, so that a direct comparison of the mentioned treatment strategies is needed to provide evidence for the optimal approach, especially in patients eligible for systemic thrombolysis. A survey of neurointerventionalists revealed that especially IVT eligibility influences the decision for or against MT in case of A2-, M3 MCA- or P2- occlusions (19). In contrast, M2 MCA occlusions, which have been shown to have unfavorable functional outcomes following their natural history (20), are already being treated in most thrombectomy centers on a regular basis (21).

Given the current uncertainty concerning the interventional treatment of MeVOs, prospective, randomized trials are needed (and are underway, i.e. the DISTAL trial and ESCAPE MeVO). These studies, however, will have to consider some obstacles compared to the LVO-MT studies, which include the proper selection of experienced thrombectomy centers (as the benefit margins will be smaller and complications might play a larger role), a proper selection of techniques, devices, and well-designed outcome measures.


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