Elena Zapata-Arriaza, MD

Compagne KCJ, van der Sluijs PM, van den Wijngaard IR, Roozenbeek B, Mulder MJHL, van Zwam WH, et al. Endovascular Treatment: The Role of Dominant Caliber M2 Segment Occlusion in Ischemic Stroke. Stroke. 2019;50:419–427.

Despite the recently demonstrated benefit of endovascular treatment (EVT) for proximal large vessel occlusion (LVO) of the anterior circulation (ICA and M1), evidence for treatment benefit of more distal occlusions, including the M2 segment of the middle cerebral artery (MCA), is limited, and further studies are necessary to address this question. In addition, the efficacy and safety of EVT in M2 occlusions remain unproven.

To determine the efficacy and safety of EVT in M2 occlusions, the authors performed an observational study with data obtained from the MR CLEAN registry. Only patients with a documented M1 or M2 target occlusion on baseline digital subtraction angiography (DSA) were included.

Caliber dominance was considered present if 1 M2 branch had a larger diameter than the other on DSA or if the perfusion defect associated with the occluded M2 branch was larger than 50% of MCA territory. Only when the diameters of both the inferior and superior branches were equal and the associated perfusion defect was ≈50% of MCA territory, the branches were considered codominant. DSA-only procedures were cases in which the target occlusion resolved or migrated too distally (M3 or M4 branches) caused by contrast flushing or manipulation with the catheter, without actual performing of intended EVT.

Primary outcome was functional outcome assessed with the modified Rankin Scale score (mRs) at 90 days. Secondary outcomes were functional independence (mRs of 0–2), stroke severity (measured using NIHSS), and change in stroke severity (assessed with delta-NIHSS, calculated as the absolute difference between baseline and follow-up NIHSS). Technical aspects included: extended Thrombolysis in Cerebral Infarction score (TICI), procedural duration, number of stent retriever passes, and procedural complications. Safety aspects included symptomatic intracranial hemorrhage and stroke progression (defined as a neurological deterioration by at least 4 points on the NIHSS).

Among 1003 included patients, 244 (24%) patients had an M2 occlusion, and 759 (76%) had an M1 occlusion. M2 occlusions had significantly lower median NIHSS scores, higher ASPECT scores, and greater intravenous thrombolysis treatment. DSA-only procedures because of reperfusion before EVT occurred more often in the M2 occlusion group. Baseline NIHSS was lower in patients with a dominant M2 occlusion than in patients with an M1 occlusion. Patients with an occlusion in a co- or nondominant division had a lower NIHSS at baseline than patients with an M1 occlusion, and they had more DSA-only procedures.

Regarding outcomes, functional outcomes were not significantly different between patients with M2 versus M1 occlusions (Figure 2). Patients with an M2 occlusion had lower follow-up NIHSS scores, but the difference in delta-NIHSS between the groups was not statistically significant. Similar successful recanalization rates were found between M1 and M2. Occurrence of symptomatic intracerebral hemorrhage or technical complications were also similar for M2 and M1 occlusions. Neurological recovery was comparable for dominant, non dominant M2, and for M1 occlusions.

Modified Rankin Scale (mRS) scores at 90 days: M1 vs M2 occlusion.

Figure 2. Modified Rankin Scale (mRS) scores at 90 days: M1 vs M2 occlusion.

Compared with M1 occlusions, the proportion of functional independence stratified by reperfusion grade was similar to patients with a dominant M2 branch (Table 3). In addition, NIHSS at follow-up and delta-NIHSS did not differ, and technical and safety aspects were either equivalent or favorable in patients with a dominant M2 division occlusion.

Proportions of Functional Independence Stratified by Reperfusion Grades.

Table 3. Proportions of Functional Independence Stratified by Reperfusion Grades.

Patients with co- or nondominant division occlusions of the M2 branch had better functional outcomes than patients with an M1 occlusion (Table 3). NIHSS at follow-up was lower in the co- or nondominant division occlusions, but delta-NIHSS was equal between both groups.

Similar results of EVT regarding functional outcomes, successful recanalization rates, symptomatic intracerebral hemorrhage or technical complications among M1 and M2 occlusion involves the main conclusions of the study. Despite limited M2 occlusions recruitment in recent clinical trials, growing evidence of EVT benefit in this MCA segment, it forces us, increasingly, to treat these patients. The originality of this paper is the EVT safety and efficacy assessment regarding M2 segment dominance.

An interesting performance of the study is related to perfused territory of the occluded arterial segment. In this sense, there are M2 occlusions (mainly the dominant ones) that work like those of M1 in terms of cerebral perfusion. This is why they have similar good functional results with similar recanalization rates. This should favour M2 occlusions EVT because it has the same clinical behavior and vascularizes a territory similar to M1, with similar technical complications. Of course, then, co- or non-dominant M2 occlusion involves better clinical outcome, possibly because the tissue at risk is smaller and this implies less ischemic damage. However, even in these M2 occlusions, the EVT performance is beneficial in clinical recovery after stroke, indicating that reperfusion of small brain regions is important, as they may involve functional area. Despite study limitations, results obtained from this article increase the reasons to treat stroke with more distal occlusions.