Bitemporal hemianopia

Overview

•Optic chiasm sits above the pituitary - crossing nasal retinal fibres (carrying temporal field information) are most vulnerable to compression

•Compression disrupts decussating fibres bilaterally → loss of temporal field in both eyes → bitemporal hemianopia; nasal fields preserved

Presentation

•Bitemporal visual field loss - upper quadrants first, progressing to full temporal loss

•Headache - bifrontal/bitemporal from raised ICP or dural stretch

•Reduced visual acuity - late feature

•Optic disc pallor on fundoscopy - longstanding compression → optic atrophy

•Endocrine symptoms by cause: amenorrhoea/galactorrhoea (prolactinoma); growth failure/short stature, polyuria/polydipsia, delayed puberty (craniopharyngioma/GH deficiency); features of hypopituitarism (fatigue, cold intolerance, reduced libido)

🚨

Child with growth failure + polyuria/polydipsia + bitemporal hemianopia = craniopharyngioma until proven otherwise. Urgent MRI required.

Investigations

🥇 First-line

•formal visual field testing (Humphrey/Goldmann perimetry) - maps and quantifies the defect; confrontation is a screen only

🏆 Gold standard

•MRI pituitary with gadolinium - definitive for chiasmal compression and tumour characterisation

•Also first-line: full pituitary hormone profile (LH, FSH, testosterone/oestradiol, prolactin, IGF-1, ACTH/cortisol, TFTs, GH)

•CT head - if MRI unavailable urgently; craniopharyngioma shows characteristic suprasellar calcification

Management

•Prolactinoma: cabergoline (dopamine agonist) - first-line; shrinks tumour and restores vision without surgery in most cases

•Non-functioning pituitary macroadenoma: trans-sphenoidal surgical resection - decompresses chiasm

•Craniopharyngioma: surgical resection (craniotomy or endoscopic endonasal) ± adjuvant radiotherapy if incompletely resected

🥈 Second-line

•stereotactic radiosurgery (Gamma Knife) for residual/recurrent pituitary adenoma; hormone replacement for hypopituitarism (hydrocortisone, levothyroxine, sex steroids, GH as indicated)

Complications

•Permanent visual loss - prolonged compression → optic atrophy; may be irreversible even after decompression

•Hypopituitarism - from tumour or as complication of surgery/radiotherapy; may require lifelong hormone replacement

•Diabetes insipidus - especially after craniopharyngioma surgery or hypothalamic involvement

🚨

Pituitary apoplexy - haemorrhage/infarction into a pituitary adenoma; sudden severe headache, acute visual loss, ophthalmoplegia - neurosurgical emergency.

💡

Visual recovery is best when decompression occurs before optic atrophy is established. In craniopharyngioma, long-term hypopituitarism and hypothalamic obesity are common regardless of visual outcome.

Causes by age

Common causes of chiasmal compression

Feature	Children	Adults
Most common cause	Craniopharyngioma	Pituitary macroadenoma (>10 mm)
Origin	Rathke's pouch remnant; suprasellar	Anterior pituitary; expands superiorly
Key imaging feature	Calcified, mixed cystic/solid on CT/MRI	Sellar/suprasellar mass on MRI
First-line treatment	Surgical resection ± radiotherapy	Cabergoline if prolactinoma; surgery if non-functioning

Localising rule

•Anterior to chiasm (optic nerve/retina) → monocular defect

•At the chiasm → bitemporal hemianopia

•Posterior to chiasm (tract, radiation, cortex) → homonymous hemianopia (most commonly stroke)

🎯

Bitemporal hemianopia = chiasmal lesion until proven otherwise.