Article Commentary: “Endovascular Treatment of Medium Vessel Occlusion Stroke”

 FYI.

Article Commentary: “Endovascular Treatment of Medium Vessel Occlusion Stroke”

• Mitch Wilson, MD, MSc

Originally published April 10, 2024 10.1161/blog.20240409.380829

Ospel JM, Nguyen TN, Jadhav AP, Psychogios MN, Clarençon F, Yan B, Goyal M. Endovascular Treatment of Medium Vessel Occlusion Stroke. Stroke. 2024;55:769–778.

The authors provide a comprehensive review of medium vessel occlusions (MeVOs) in stroke and discuss important issues regarding their definition, detection, and treatment.

In contrast to large vessel occlusions (LVOs), defining MeVOs is not as straightforward. Large vessel occlusions (LVOs) are defined solely on anatomic grounds and by most conventions encompass occlusions of large, proximal arteries such as the intracranial internal carotid artery, M1 segment of the middle cerebral artery, and the basilar artery. LVOs often present with severe deficits that are disabling if left untreated. MeVOs, on the other hand, generally present with milder deficits, with one-third patients meeting the traditional criteria of NIHSS score of <6 for minor stroke. Furthermore, there is no universal definition to distinguish between the distal M1 and proximal M2 segment, or between M2/M3 or A2/A3. The authors believe that a composite definition of MeVO that considers both the anatomic location and the severity of deficit is helpful for guiding management. One such composite definition has been proposed.¹

Given their smaller size and more distal location compared to LVOs, MeVOs are frequently missed on initial CT angiography (CTA). The review highlights one recent observational study of patients presenting with ischemic stroke in which 35% of M2 occlusions were missed using single-phase CTA.² Advanced imaging techniques, such as multiphase CTA, CT perfusion, and MRI, have been shown to increase the detection rate of MeVOs, although these imaging modalities are not available in the hyperacute setting in many clinical centers. Other potential strategies include ongoing physician training in detecting MeVOs, having multiple physicians review the CTA, and cross-referencing the thin slice source axial cuts with axial, coronal, and sagittal maximum intensity projection (MIP) reformats. 

Compared to the endovascular management of LVOs, the magnitude of benefit derived from EVT in MeVO is almost certainly smaller given the less disabling deficits. The procedural EVT complication risk is higher in MeVOs, mainly owing to higher rates of vessel perforation and hemorrhage that are believed to be related to smaller vessel diameter, increased vessel tortuosity, and lack of devices designed specifically for MeVOs. Acknowledging the reduced efficacy and increased rates of hemorrhage in patients with MeVO compared to LVO, patients with MeVO selected for EVT should, therefore, have deficits severe enough to justify the treatment. Although using an NIHSS score <6 for minor stroke could serve as a cut-off for avoiding EVT, about one third of patients with minor stroke do not regain functional independence (modified Rankin score ≥ 2) at 90 days. Another important consideration is whether the patient’s deficits are fully explained by the MeVO. If a patient’s deficits are more severe than would be expected based on the location of the MeVO, then there is a high probability that the patient has a secondary MeVO that resulted from the migration of a more proximal thrombus and thus retrieval of the MeVO would be of minimal benefit. 

While there are no published randomized controlled trials (RCTs) regarding EVT in MeVO, there are currently 5 ongoing RCTs that will help to determine its efficacy and safety and potentially identify which patients are the best candidates for the procedure.