Diving into a Shallow Pool: Endovascular Treatment for Basilar Artery Occlusion.

E therapy for emergent large vessel occlusion ischemic stroke has come a long way in the past decade. Multiple large multicenter randomized controlled trials have demonstrated the efficacy of mechanical thrombectomy in the cerebral anterior circulation, including the intracranial internal carotid artery and the proximal segments of the middle cerebral artery (1–4). Posterior circulation emergent large vessel occlusion strokes, particularly those involving basilar artery occlusion, have not been subjected to such rigorous randomized evaluation because of their rarity (they account for about 1%–5% of all emergent large vessel occlusion strokes), complex symptoms, and severity. Case series thus remain the backbone of clinical evidence in basilar artery occlusion. In this issue of Radiology, Baik et al (5) evaluate the success rates for recanalization and the clinical outcomes of patients with CT angiography–proven basilar artery occlusion who were treated with endovascular therapy within 12 hours of symptom onset. Not only did the authors use modern neuroendovascular techniques— including mechanical thrombectomy by using stent retrievers, aspiration catheters with or without adjunctive thrombolysis, and balloon or stent angioplasty—but they also separated recanalization rates and outcomes on the basis of the underlying pathologic structure of basilar and vertebral arteries. Baik et al divided their patients into three groups: group 1, embolism without vertebral artery steno-occlusion; group 2, embolism from tandem vertebral artery steno-occlusion; and group 3, in situ atherosclerotic thrombosis. The mean time to initiation of endovascular therapy was between 3.5 and 4 hours across groups, reflecting prompt recognition of stroke symptoms and efficient stroke diagnosis and treatment. As expected, group 1 had the shortest time to recanalization, and groups 1 and 2 had better basilar artery recanalization rates (85%) than did group 3 (55%). The same research group recently published (6) their results treating emergent large vessel occlusion patients with and without in situ intracranial atherosclerotic stenosis. By including both the cerebral anterior and posterior circulations, the authors found that primary mechanical thrombectomy was almost 94% successful in recanalization for patients without intracranial atherosclerotic stenosis and only 29% successful in those with intracranial atherosclerotic stenosis; 84% of the intracranial atherosclerotic stenosis patients needed additional treatments such as angioplasty, stent placement, or antiplatelet medication. Unlike anterior circulation emergent large vessel occlusion randomized controlled trials, in which antiplatelet medication infusions and adjunctive angioplasty and stent placement were often excluded as protocol violations, these case series reflect so-called real-world practice by experienced neurointerventionalists. Despite this proactive treatment approach, symptomatic hemorrhagic complications were rare in the current series (6). Clinical outcomes differed between the groups. Whereas 53% of patients in group 1 had good clinical outcomes (ie, were functionally independent 90 days after stroke), only 29% of patients in group 2 and 20% of patients in group 3 had good clinical outcomes. Baseline core infarction volumes were not reported, although estimating brainstem and cerebellar infarction volumes from the CT and CT angiography triage protocol can be difficult. In their other recent series (6) that combined all patients with emergent large vessel occlusion with or without in situ intracranial atherosclerotic stenosis, the same research group reported good outcomes of 46% and 47%, respectively. Comparison of the results of Baik et al (5) to those of recent cerebral anterior circulation randomized controlled trials is also instructive. Patients in group 1 with basilar artery occlusion had outcomes similar to those observed at the mechanical thrombectomy arm of the endovascular treatment for small core and proximal occlusion ischemic stroke (ESCAPE) trial (2) (53% functional independence at 90 days), which also allowed enrollment of patients up to 12 hours after stroke symptom onset. Similar to the current study, the ESCAPE trial did not use perfusion imaging selection, although it did use multiphasic CT angiography to help estimate collateral blood flow in the brain. The clinical mismatch in the triage of wake up and late presenting strokes undergoing neurointervention with Trevo (DAWN) trial (7) enrolled patients between 6 and 24 hours after they were last observed as healthy; the DAWN investigators used diffusion MRI or CT perfusion imaging to exclude from therapy patients who had core infarctions of over 50 mL at the time of triage. The DAWN trial reported 49% functional independence at 90 days. In other words, patients with an embolus to an otherwise normal basilar artery and normal vertebral arteries (group 1 from Baik et al) had a similar rate of good outcome as did those in randomized controlled trials for cerebral anterior circulation. However, patients who had stenosis or Diving into a Shallow Pool: Endovascular Treatment for Basilar Artery Occlusion