Vascular Supply of the Occipital Lobe Explains Why Certain Patterns of Visual Field Loss from Embolic Stroke Are Common and Others Are Prohibited

The cerebral cortex is supplied by microvascular lobules, comprised of half a dozen penetrating arterioles surrounding a single, central draining venule. Surface arterioles that supply penetrating arterioles form an anastomotic plexus. Consequently, embolic occlusion of a small surface vessel does not cause a local infarct, because collateral flow is available. Nor does an infarct occur after occlusion of a single penetrating arteriole. Infarction of striate cortex requires occlusion of a major arterial trunk vessels - e.g., the inferior or superior calcarine artery. The fixed relationship between the vascular supply of the occipital lobe and the retinotopic map causes stereotypical patterns of visual field defects after stroke. In this lecture, allowed and forbidden scotomas will be reviewed and explained.