A 35-year-old woman presents with bitemporal hemianopia. A coronal MRI of the brain demonstrates a mass arising from the sella turcica extending upward. The structure lying immediately superior to the tumour and responsible for the visual defect is the:

• A Optic tract
• B Anterior cerebral artery
• C Mammillary body
• D Optic chiasm ✓

Explanation

The optic chiasm lies in the suprasellar region directly above the diaphragma sellae, so an enlarging pituitary macroadenoma compresses its decussating nasal retinal fibres, causing bitemporal hemianopia. The optic tracts lie posterolateral to the chiasm and compression there produces homonymous defects. The mammillary bodies are posterior to the chiasm, and although the anterior cerebral arteries are nearby they do not explain the field loss.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.