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INTRODUCTION

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Vertebrobasilar arterial disease has a heterogeneous, clinical presentation that depends on the underlying pathophysiology of the lesion. Regardless of etiology, however, vertebrobasilar arterial strokes can be devastating and have, until recently, been associated with a high rate of death and disability. With technical advances in neuroimaging and endovascular procedures, as well as data from randomized, clinical trials on stroke prevention and management of acute stroke, we have gained a better understanding of the pathophysiology and treatment options for vertebrobasilar disease. Although currently there is not always definitive data to guide the treatment of choice, immediate expert evaluation by a stroke neurologist may help in selecting the appropriate imaging modality and treatment plan that can often be lifesaving.

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ANATOMY

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Vertebral Artery

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The anatomic course of the vertebral artery (VA) is divided into four segments. The first segment (V1) lies between the origin of VA from the subclavian artery (SA) and the transverse foramen of C5 or C6. The second segment (V2) is located within the transverse foramina from C5 or C6 to C2. The third segment (V3), also known as the vertebral siphon, courses posteriorly and laterally between the atlas and occiput. The fourth segment (V4) is the intracranial portion of the VA; the vessel pierces the dura mater and enters the cranium through the foramen magnum, then courses medially and superiorly to merge with the opposite VA at the level of pontomedullary junction giving rise to the basilar artery (BA).

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The left VA originates directly from the aortic arch in approximately 8% of cases. Asymmetry between the vertebral arteries is found in 66% of cases with the left VA being dominant in 45% cases.1 The VA has three major intracranial branches: anterior spinal artery, posterior spinal artery, and posterior inferior cerebellar artery (PICA).

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The anterior spinal artery is a midline unpaired vessel formed by anastamosis of two branches from each VA. It originates at the level of the olivary nucleus to the conus medullaris and descends caudally to supply to the ventral surface of the medulla and the anterior two-thirds of the spinal cord.

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The posterior spinal artery is a branch of either the VA or PICA and supplies the posterior third of the spinal cord.

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The PICA is usually the largest branch of the distal intracranial portion of the VA, branching in close proximity to the BA origin. Fifteen percent of individuals lack one PICA and 5% have a hypoplastic PICA. Additionally, a PICA originating from the proximal BA directly or from a common trunk with AICA can be occasionally seen.1 The lateral medulla, inferior cerebellar vermis, and inferior surface of the cerebellum are supplied by the PICA.

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Basilar Artery

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The BA lies ventral to the pons and extends from the pontomedullary junction to the pontomesencephalic junction where it ...

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