Cerebrovascular Anatomy: Special Considerations

Abstract

The brain-supplying arteries can be divided into two communicating circulatory systems: the anterior and the posterior circulation. The anterior circulation originates in both internal carotid arteries (ICA) and in part from both external carotid arteries (ECA) if a high-grade stenosis of the ipsilater-al ICA is present. The posterior circulation arises from both vertebral arteries and the unpaired basilar artery. The posterior and anterior circulation is connected via the circle of Willis, which is known to have a very heterogeneous anatomical structure. The circle of Willis is a vascular polygon with ten components: both ICAs, both posterior communicating arteries (PCoAs), the single anterior communicating artery (ACoA), the anterior cerebral arteries (ACAs), the posterior cerebral arteries (PCAs), and the basilar artery (BA). Circle of Willis is an inefficient collateral in 50% of subjects due to insufficient communication between the anterior and the posterior circulation, and between the left-sided and the right-sided circulation secondary to the hypoplasia of the PCoA and ACoA respectively.