A 45-year-old woman with a tumour in the deep white matter of the left temporal lobe reports difficulty seeing objects in the upper right quadrant of both visual fields. Which structure is most likely compressed?
- A Meyer's loop ✓
- B Optic radiations in the parietal lobe
- C Optic chiasm
- D Lingual gyrus of the occipital lobe
Correct answer: A. Meyer's loop
Explanation
Meyer's loop consists of fibres of the optic radiation that sweep forward into the temporal lobe before passing back to the calcarine cortex. These fibres carry the contralateral superior visual quadrant information, so a temporal lobe lesion produces a contralateral superior quadrantanopia, classically described as pie in the sky. Parietal lobe radiation fibres carry the inferior quadrant, so their damage causes an inferior quadrantanopia, which eliminates option B.
Reference: Gray's Anatomy, 42nd ed.
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Written and medically reviewed by the StethoPrep medical team.