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Topic

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Optic canal

The optic canal is a short, cylindrical bony passage located at the orbital apex, within the sphenoid bone. It serves as the conduit through which the optic nerve (cranial nerve II) and ophthalmic artery traverse from the cranial cavity into the orbit. Precise knowledge of the optic canal’s anatomy and radiological appearance is crucial for diagnosing lesions, trauma, and diseases affecting the visual pathway.

Synonyms

  • Optic foramen

  • Canalis opticus

Function

  • Transmits the optic nerve (cranial nerve II) from the brain to the orbit

  • Allows passage of the ophthalmic artery

  • Serves as a critical structure in the visual pathway, connecting the eye to the brain

MRI Appearance

  • T1-weighted imaging:

    • The bony walls appear as low signal (dark) structures.

    • The optic nerve within the canal demonstrates intermediate to low signal intensity.

    • The surrounding fat (in the orbital apex) appears hyperintense (bright).

  • T2-weighted imaging:

    • The optic nerve appears hyperintense relative to the bone (which remains hypointense).

    • Cerebrospinal fluid (CSF) within the nerve sheath may be seen as a hyperintense rim around the nerve.

  • STIR (Short Tau Inversion Recovery):

    • The bony walls appear as low signal (dark) structures.

CT Appearance

  • The optic canal appears as a well-defined, short bony tunnel in the sphenoid bone, visualized best on thin axial or coronal sections.

  • The canal is seen as a round or oval lucency (dark) through the dense sphenoid bone.

  • Any bony abnormalities, fractures, or narrowing (stenosis) can be readily identified.

  • Contrast CT may help delineate vascular structures adjacent to the canal.

MRI images

Optic canal mri image