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Primary visual cortex lesion — MRCPsych Paper A MCQ

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ModerateNeuroanatomyPrimary visual cortex lesionMRCPsych Paper A

A 72-year-old woman develops a right homonymous hemianopia following an ischaemic stroke. Central vision is relatively spared, and MRI shows an infarct confined to the medial left occipital lobe around the calcarine sulcus. Which structure is most directly affected?

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Correct answer: B — Left primary visual cortex

The correct answer is **B, left primary visual cortex**. The primary visual cortex lies around the calcarine sulcus in the medial occipital lobe. Each visual cortex represents the contralateral visual hemifield, so a left-sided lesion causes right homonymous visual-field loss. Relative macular sparing is also characteristic of occipital cortical infarction, although the MRI localisation is decisive here. A left lateral geniculate lesion can cause right homonymous hemianopia but is excluded by the cortical MRI location. Lesions of the right optic tract or right primary visual cortex would cause left homonymous hemianopia. An optic chiasm lesion classically causes a heteronymous, usually bitemporal, field defect rather than homonymous hemianopia.

Reference: PubMed, “Splenial Callosal Disconnection in Right Hemianopic Patients Induces Right Visual-Spatial Neglect,” 2022. https://pubmed.ncbi.nlm.nih.gov/35625026/