A 62-year-old man with a right temporal lobe glioma reports difficulty seeing objects in his lower left visual field. Formal perimetry confirms a left homonymous superior quadrantanopia. Which structure has been interrupted?

• A Right calcarine cortex above the calcarine sulcus
• B Optic radiation fibres in the right parietal lobe
• C Right optic tract
• D Meyer's loop of the optic radiation in the right temporal lobe ✓

Explanation

Meyer's loop carries fibres from the inferior retinal quadrant, which represent the contralateral superior visual field, and it sweeps through the temporal lobe before joining the main optic radiation. D lesion here produces a contralateral superior quadrantanopia, classically described as the pie in the sky defect. Parietal lobe involvement of the radiation gives the opposite pattern, an inferior quadrantanopia, because those fibres carry superior field information.

Reference: Snell's Clinical Neuroanatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.