Optic chiasm

Last revised by Rohit Sharma on 3 Apr 2024

Citation, DOI, disclosures and article data

Citation:

Hacking C, Sharma R, Gaillard F, et al. Optic chiasm. Reference article, Radiopaedia.org (Accessed on 24 Apr 2024) https://doi.org/10.53347/rID-52110

DOI:

https://doi.org/10.53347/rID-52110

Permalink:

https://radiopaedia.org/articles/52110

rID:

52110

Article created:

22 Mar 2017, Craig Hacking ◉ ◈

Disclosures:

At the time the article was created Craig Hacking had no recorded disclosures.

View Craig Hacking's current disclosures

Last revised:

3 Apr 2024, Rohit Sharma ◉

Disclosures:

At the time the article was last revised Rohit Sharma had no financial relationships to ineligible companies to disclose.

View Rohit Sharma's current disclosures

Revisions:

19 times, by 13 contributors - see full revision history and disclosures

Systems:

Central Nervous System

Sections:

Anatomy

Synonyms:

optic chiasma
chiasm

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.

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. However, this has been suggested to possibly be artifactual ^ref.

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.