A 52-year-old man presents because he keeps bumping into doorframes on both sides and recently narrowly missed a cyclist approaching from his left. His central vision is 6/6 and he has no headache, but his wife notes he seems to miss food on the sides of his plate. This has crept up over a year.
Examination Findings
Visual acuity 6/6 each eye, colour vision slightly reduced. Confrontation and automated perimetry: bitemporal hemianopia respecting the vertical midline, denser superiorly (a ‘pie in the sky’ quadrantic start that has progressed). Optic discs: bilateral temporal pallor with a band pattern. Pupils normal, movements full. Endocrine review reveals reduced libido and fatigue over the same period.
Investigations
MRI of the brain with dedicated pituitary views — the definitive test — shows a pituitary macroadenoma compressing the optic chiasm from below. Formal visual fields document the defect. Endocrine workup (prolactin and full pituitary panel) with endocrinology. Baseline fields and OCT for post-treatment comparison.
Questions to Think About
- Why does a chiasmal lesion respect the vertical midline?
- Why did central vision stay 6/6 while the fields collapsed?
- Which extra-ocular clues pointed to the pituitary?
Diagnosis
Bitemporal hemianopia due to optic chiasm compression by a pituitary macroadenoma.
Reasoning
Reasoning: The nasal retinal fibres — which see the temporal fields — cross at the chiasm, so a mass compressing the chiasm from below knocks out both temporal fields in a defect that respects the vertical midline: the signature of chiasmal compression. Central acuity survives early because the macular fibres are relatively resistant and the compression starts superiorly (the inferior nasal fibres, serving superior temporal field, are compressed first by a pituitary mass growing upward). The slow course, the band (bow-tie) optic atrophy, and the endocrine symptoms — fatigue, reduced libido — complete the pituitary picture. Diagnosis: bitemporal hemianopia from a pituitary macroadenoma compressing the optic chiasm. Management: typical management includes urgent joint neurosurgical-endocrine-ophthalmic care: most such adenomas are removed via transsphenoidal surgery, with prolactinomas sometimes managed medically per endocrinology. Fields often improve after decompression — earlier surgery gives better recovery — and lifelong endocrine and ophthalmic follow-up continues. He is told the doorframes were his visual fields warning him, and that treatment aims to halt and partly reverse the loss.
Differential Diagnosis
- Glaucoma — ruled out: glaucomatous defects respect the horizontal midline and start arcuate; these respect the vertical midline.
- Tilted myopic discs with field artefacts — ruled out: refractive error is mild and the defect is a clean hemianopia.
- Bilateral occipital lesions — ruled out: congruent homonymous defects would result, not bitemporal; MRI shows the chiasmal mass.
Management
Typical management includes urgent referral to neurosurgery and endocrinology, transsphenoidal resection for most macroadenomas (or medical therapy for prolactinomas per endocrinology), pre- and post-operative visual field and OCT documentation, and long-term endocrine replacement and tumour surveillance as needed. Vision is monitored for recovery, which is best when decompression is early.
Key Learning Points
- Chiasmal defects respect the vertical midline; retinal/optic-nerve defects respect the horizontal.
- A pituitary mass compresses from below: superior temporal quadrants go first.
- Band (bow-tie) optic atrophy is the chronic signature of chiasmal compression.
- Ask about endocrine symptoms in every bitemporal hemianopia — fatigue, libido, periods, galactorrhoea.
Red Flags
- Bitemporal field loss — chiasmal compression until proven otherwise; image promptly.
- Endocrine symptoms with visual field loss — the pituitary declares itself twice.
- Sudden worsening with severe headache (pituitary apoplexy) — emergency.
Educational content only — not medical advice. Clinical decisions must be made by a qualified professional for the individual patient.
Discuss this case with colleagues in the comments below.