Inclusion criteria:

1. Signs and symptoms consistent with an acute posterior circulation ischemic stroke
2. mRS 0-2 at baseline for patients age 18-89. Patients ≥90 should be fully independent in all of their activities of daily living prior to stroke onset.
3. Age ≥18 years; patients ≥90 years must be fully independent in all activities of daily living prior to the stroke.
4. Baseline National Institutes of Health Stroke Scale Score ≥4 and remains ≥4 immediately prior to thrombectomy treatment
5. Stroke symptoms began within 48 hours of thrombectomy treatment. Stroke onset is defined as the time the patient was last known to be at his/her neurologic baseline. Wake-up strokes are eligible if they meet the above time limits.
6. Endovascular thrombectomy for PC-LVO planned as standard-of-care therapy. Patients may be treated by endovascular therapy that includes aspiration or mechanical thrombectomy, angioplasty, stent placement, or intravenous/intra-arterial GPIIb/IIIa inhibitor infusion
7. Time of arterial puncture (femoral or radial artery) occurred (or expected to occur) within 120 minutes of CT or MR imaging study completion
8. Patient or Legally Authorized Representative has signed the study Informed Consent form

Exclusion criteria:

1. Other serious, advanced, or terminal illness (investigator judgment) or life expectancy is less than 6 months
2. Pre-existing medical, neurological, or psychiatric disease that would confound the neurological or functional outcomes evaluation
3. Any condition that, in the opinion of the investigator, precludes an endovascular procedure or poses a significant hazard to the subject if an endovascular procedure was performed

Imaging inclusion criteria:

1. Planned to undergo standard neuroimaging evaluation by computed tomography (CT) or magnetic resonance (MR) imaging that includes CT or MR angiography or the intracranial circulation and cerebral perfusion imaging prior to thrombectomy
2. Vertebral artery or basilar artery occlusion or severe stenosis on CTA or MRA. (Alternative assessment if MRA/CTA technically inadequate or > 120 minutes old is cerebral perfusion imaging consistent with a basilar or vertebral artery occlusion)
3. Absence of cerebral hemorrhage on baseline CT or MRI

Imaging exclusion criteria:

1. Acute symptomatic arterial occlusions in more than one vascular territory on CTA (ie – associated anterior circulation LVO of the internal, middle, or anterior cerebral artery
2. Evidence of intracranial tumor (except small meningioma), acute intracranial hemorrhage, neoplasm or arteriovenous malformation
3. Mass effect with significant herniation above the cerebral tentorium or below the foramen magnum
4. Intracranial stent implanted in the same vascular territory that precludes safe deployment/removal of neurothrombectomy device