The optic chiasm is the site where the two optic nerves cross.
Anatomy
The optic chiasm is located in the middle cranial fossa within the sulcus chiasmatis of the sphenoid bone. In its immediate vicinity, the floor and anterior wall of the third cerebral ventricle meet. Inferior to the chiasm lies the sella turcica with the pituitary gland, and posteriorly lies the pituitary stalk.
Anatomical variants
| Variant | Optic chiasm location1 | Frequency2 |
|---|---|---|
| Normal | Above the diaphragma sellae | ~ 80 % |
| Prefixed | Above the tuberculum sellae | ~ 10 % |
| Postfixed | Above the dorsum sellae | ~ 10 % |
Clinical relevance
Tumors in the region of the pituitary gland, such as pituitary adenomas or craniopharyngiomas, can cause displacement or compression of the optic chiasm, resulting in visual field defects, typically a bitemporal hemianopia, or visual impairment.
Imaging
The optic chiasm can be visualized on MRI.
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