Macular sparing in a PCA territory stroke is explained by what vascular mechanism?

• A. The macula has dual blood supply from MCA and PCA, providing collateral flow.
• B. Blood flow to the macula is supplied solely by the PCA.
• C. Blood flow to the macula is supplied by the anterior choroidal artery.
• D. The macula has independent microcirculation unaffected by PCA occlusion.

Answer: (A)

Macular sparing is explained by collateral vascular supply to the macular region of the visual cortex. The macula, represented in the posterior calcarine cortex of the occipital lobe, receives perfusion from both the posterior cerebral artery and branches of the middle cerebral artery. If a stroke affects the PCA territory, the middle cerebral artery’s supply can continue to perfuse the macular area, preserving central vision, while the surrounding occipital cortex tied to the PCA loses blood flow and produces the typical contralateral homonymous hemianopia. The other potential sources (like the anterior choroidal artery) don’t provide the primary macular perfusion, and the macula isn’t supplied by an entirely independent microcirculation in this context.