Background purpose:
Clinical outcome of patients suffering from acute ischemic stroke (AIS) in the anterior cerebral circulation depends on onset-to-reperfusion time (OTRT). Therefore, clinical outcome of patients with AIS in the posterior circulation probably depends on OTRT, too. Transfemoral approach is common but limited by aortic or peripheral artery conditions and then transbrachial access is an alternative. 
Hypothesis:
There are anatomical features of the vertebral artery that transbrachial access makes it easier to navigate thrombectomy catheters into the basilar artery than transfemoral one.
Methods:
We included in our retrospective study patients 1) who were admitted to our institution from October 1st, 2013 to March 1st, 2018, 2) who were diagnosed as acute ischemic stroke due to the basilar artery occlusion, 3) who  underwent cerebral-cervical-thoracic 3D-CT scanning and transbrachial thrombectomy via the dominant sided vertebral artery for access to the basilar artery. 
We evaluated the patient’s baseline features, the dominant sided vertebral artery, the diameter of the dominant sided vertebral artery at the level of the fourth cervical vertebral body, the angle formed by the dominant sided vertebral artery and the subclavian artery, the success rate of the navigation into the basilar artery.

Results:
Twelve patients matched our inclusive criteria and were analyzed. Median age was 78 years, 8 patients ( 62%) were men, eight right vertebral arteries (62%) were dominant. The diameter of the dominant sided vertebral artery ranged from 3.33 to 4.84mm and its median diameter was 4.35mm. The angle formed by two arteries ranged from 47 to 98 degree and its median angle was 68 degree. Penumbra system was used in 8 patients, stent retrievers in 2 patients, both of Penumbra system and stent retrievers in 2 patients. No transbrachial approach was abandoned. 

Conclusion:
The diameter of the dominant sided vertebral artery of 3.33 mm or more and the angle formed by the subclavian and vertebral arteries of 47 degree or more are anatomical features of the vertebral artery that transbrachial access is more appropriate to navigation of thrombectomy catheters into the basilar artery.

Anatomical features of the vertebral artery for transbrachial approach for emergency thrombectomy in the ischemic posterior circulation stroke