Background and PurposeData on the management of large vessel occlusion in patients with anterior circulation acute ischemic stroke (AIS) due to underlying intracranial stenosis are scarce. The aim of this retrospective study was to compare endovascular treatment and outcome in AIS patients with and without underlying stenosis of the M1 segment.Materials and MethodsA total of 533 acute stroke patients with an isolated M1 occlusion who underwent mechanical thrombectomy between 02/2010 and 08/2017 were included. Underlying intracranial atherosclerotic stenosis (ICAS) was present in 10 patients (1.9%), whereas 523 patients (98.1%) had an embolic occlusion without stenosis.ResultsThere was no difference in age, admission National Institutes of Health Stroke Scale, risk factors, Alberta stroke program early CT score or collaterals between the groups. Procedure time (155 vs 40 min, P = 0.001) was significantly longer in the ICAS group where rescue stent-angioplasty was performed in all patients. There was no statistical difference in final modified thrombolysis in cerebral infarction score between both groups (70 vs 88%, P = 0.115). Favorable outcome (modified Rankin Scale ≤ 2) at 90 days was less frequent in patients with ICAS than in the embolic group (0 vs 49.4%, P = 0.004). The mortality rate tended to be higher in the ICAS group (44.4 vs 19.4%, P = 0.082).ConclusionIn patients with AIS, rescue therapy with stent placement to treat underlying ICAS of the M1 segment is technically feasible; however, in our study, a significantly lower rate of favorable outcome was observed in these patients compared to those with thromboembolic M1 occlusions.Level of EvidenceLevel 3, non-randomized controlled study.