A 48-year-old man with a left temporal lobe tumour reports difficulty seeing objects in one quadrant. Visual field testing shows a right superior homonymous quadrantanopia. Which structure is involved?
- A Left parietal optic radiation
- B Meyer's loop in the left temporal lobe ✓
- C Right calcarine cortex above the sulcus
- D Left lateral geniculate body
Correct answer: B. Meyer's loop in the left temporal lobe
Explanation
Meyer's loop carries fibres from the inferior retina, which represent the contralateral superior visual field. It sweeps through the temporal lobe, so a left temporal lesion produces a right superior homonymous quadrantanopia, classically called pie in the sky. Parietal radiation fibres serve the inferior field, and a calcarine lesion would produce a congruous quadrantic defect with macular sparing tendencies rather than an isolated quadrant from a mass.
Reference: Snell's Clinical Neuroanatomy, 8th ed.
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