Optic chiasm
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Updates to Article Attributes
The optic chiasm or chiasma is the midline structure where the nasal (medial) fibres of the optic nerves decussate to continue posteriorly as the optic tracts. It lies in the chiasmatic cistern and along with the pituitary stalk, is completely encircled by the circle of Willis.
Gross anatomy
Relations
The circle of Willis encircles the pituitary stalk and optic chiasma.
- lateral: anterior perforated substance
- anterior: optic nerves
- posterior: optic tracts, tuber cinereum, pituitary stalk, mammillary bodies, posterior perforated substance
- superior: supraoptic recess of the third ventricle, anterior commissure
- superoposterior: hypothalamus
- inferior: suprasellar cistern
The anterior-to-posterior location of the chiasm relative to the pituitary fossa is variable 4:
- prefixed: tuberculum sellae (15%)
- normal: diaphragma sellae (70%)
- postfixed: dorsum sellae (15%)
Historically, it has been believed that the crossing fibres made an anterior bend into the prechiasmatic optic nerve; this is known as Wilbrand knee. More recent work, however, has suggested this is artifactual.
Blood supply
Small branches of the anterior cerebral artery and the superior hypophyseal artery supply the chiasm and intracranial portion of the optic nerves whereas the optic tracts are supplied by small branches of the anterior choroidal and posterior communicating arteries.
Related pathology
Lesions compressing the chiasm classically produce the visual field defect of bitemporal hemianopia, where there is loss of the temporal fields.
-</ul><h4>Blood supply</h4><p>Small branches of the <a href="/articles/anterior-cerebral-artery">anterior cerebral artery</a> and the <a href="/articles/superior-hypophyseal-artery">superior hypophyseal artery</a> supply the chiasm and intracranial portion of the optic nerves whereas the optic tracts are supplied by small branches of the <a href="/articles/anterior-choroidal-artery">anterior choroidal</a> and <a href="/articles/posterior-communicating-artery">posterior communicating arteries</a>.</p><h4>Related pathology</h4><p>Lesions compressing the chiasm classically produce the <a href="/articles/visual-pathway-defecits">visual field defect</a> of bitemporal hemianopia, where there is loss of the temporal fields.</p>- +</ul><p>Historically, it has been believed that the crossing fibres made an anterior bend into the prechiasmatic optic nerve; this is known as <a title="Wilbrand knee (optic radiation)" href="/articles/wilbrand-knee-optic-radiation">Wilbrand knee</a>. More recent work, however, has suggested this is artifactual. </p><h4>Blood supply</h4><p>Small branches of the <a href="/articles/anterior-cerebral-artery">anterior cerebral artery</a> and the <a href="/articles/superior-hypophyseal-artery">superior hypophyseal artery</a> supply the chiasm and intracranial portion of the optic nerves whereas the optic tracts are supplied by small branches of the <a href="/articles/anterior-choroidal-artery">anterior choroidal</a> and <a href="/articles/posterior-communicating-artery">posterior communicating arteries</a>.</p><h4>Related pathology</h4><p>Lesions compressing the chiasm classically produce the <a href="/articles/visual-pathway-defecits">visual field defect</a> of bitemporal hemianopia, where there is loss of the temporal fields.</p>
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