Optic chiasm
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%)
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 title="Visual pathway deficits" href="/articles/visual-pathway-defecits">visual field defect</a> of bitemporal hemianopia, where there is loss of the temporal fields.</p>- +</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>
Image 1 Diagram ( create )
Image 2 MRI (STIR) ( update )
Image 4 Diagram ( update )
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