A solid understanding of the pathophysiology of a posterior cerebral artery (PCA) stroke as well as the syndrome relating to it, requires adequate knowledge of the structures and vascular anatomy of the brain. Anterior and posterior circulations provide the primary blood circulation of the brain. Both circulations are connected by the posterior communicating arteries (PCOM), which make up the circle of Willis. When there is an occlusion in the cerebral vasculature, the circle of Willis, as well as collateral circulations, provide blood to the occluded areas. Posterior circulation is supplied by the vertebral arteries (VA), posterior inferior cerebellar arteries (PICA), basilar artery (BA), anterior inferior cerebellar arteries (AICA), pontine branches of the basilar artery, superior cerebellar arteries (SCA), PCA, and PCOM. The VAs arise from the subclavian arteries and fuse into the BA within the cranium. The BA typically divides into PCAs near the pituitary stalk at the pontomesencephalic junction. PCAs can originate from BA 70 percent of the time, 20 percent of the time from PCOMs, and 10 percent of the time from a mix of the two. The PCAs then give off branches to the midbrain, subthalamic nucleus, basal nucleus, thalamus, temporal, occipital, and occipitoparietal cortices (See Figure). PCA is divided into four segments, P1 to P4. The segments can be further categorized into deep and superficial segments or proximal and distal, respectively.