Key Concepts
Introduction
Brainstem stroke syndromes represent a group of distinct clinical entities caused by ischemic or hemorrhagic events affecting specific regions of the brainstem (midbrain, pons, and medulla oblongata). The brainstem receives its blood supply from the vertebrobasilar arterial system: the two vertebral arteries (arising from the subclavian arteries) ascend through the transverse foramina of the cervical vertebrae and enter the skull through the foramen magnum, coursing along the ventral surface of the medulla. The vertebral arteries give off branches including the posterior inferior cerebellar artery (PICA) and the anterior spinal artery before merging at the pontomedullary junction to form the basilar artery. The basilar artery ascends along the ventral surface of the pons, giving off paired circumferential branches including the anterior inferior cerebellar artery (AICA) and the superior cerebellar artery (SCA), as well as numerous small perforating (paramedian and short circumferential) branches that supply the pontine tegmentum and basis pontis. At the upper border of the pons, the basilar artery bifurcates into the two posterior cerebral arteries (PCAs), completing the posterior circulation contribution to the Circle of Willis. Understanding this vascular...