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At the time the article was created Craig Hacking had no recorded disclosures.View Craig Hacking's current disclosures
At the time the article was last revised Frank Gaillard had the following disclosures:
- Radiopaedia Australia Pty Ltd, Founder and CEO (ongoing)
- Biogen Australia Pty Ltd, Investigator-Initiated Research Grant for CAD software development in multiple sclerosis (past)
These were assessed during peer review and were determined to not be relevant to the changes that were made.View Frank Gaillard's current disclosures
The optic chiasm or chiasma is the midline structure where the nasal (medial) fibers 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.
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 fibers made an anterior bend into the prechiasmatic optic nerve; this is known as Wilbrand knee. More recent work, however, has suggested this is artifactual.
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.
Lesions compressing the chiasm classically produce the visual field defect of bitemporal hemianopia, where there is loss of the temporal fields.
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