A lesion in the visual cortex causing a homonymous hemianopia with macular sparing is most likely located in which brain region?

A lesion in the visual cortex causing a homonymous hemianopia with macular sparing is most likely located in which brain region?

• A. Occipital lobe (calcarine cortex)
• B. Frontal lobe
• C. Temporal lobe
• D. Parietal lobe

Answer: (A)

The key idea is that the primary visual cortex sits in the occipital lobe along the calcarine fissure and maps the opposite visual field for each eye. A lesion there disrupts the contralateral half of the visual field in both eyes, producing a homonymous hemianopia. The macula is spared because its representation in the cortex is especially large and often has input that can be preserved or supported by collateral blood supply, so central vision stays intact even when surrounding occipital cortex is damaged. That pattern points to the occipital lobe, specifically the calcarine cortex, as the most likely location. Frontal, temporal, or parietal lesions produce different visual-field patterns (for example, quadrant defects due to involvement of Meyer's loop or dorsal/ventral stream pathways), which don’t match this presentation as well.

The key idea is that the primary visual cortex sits in the occipital lobe along the calcarine fissure and maps the opposite visual field for each eye. A lesion there disrupts the contralateral half of the visual field in both eyes, producing a homonymous hemianopia. The macula is spared because its representation in the cortex is especially large and often has input that can be preserved or supported by collateral blood supply, so central vision stays intact even when surrounding occipital cortex is damaged. That pattern points to the occipital lobe, specifically the calcarine cortex, as the most likely location. Frontal, temporal, or parietal lesions produce different visual-field patterns (for example, quadrant defects due to involvement of Meyer's loop or dorsal/ventral stream pathways), which don’t match this presentation as well.