CT sign of optic nerve (Optic track sign)

Image representation

Most pronounced
on enhanced cross-sectional optic nerve CT or fat suppressed T1-weighted magnetic resonance images.
On these images, the optic nerve appears as strip-like low-density (signaling) bands
relative to the reinforced optic sheath on its sides.

interpretation

The optic nerve orbital sign is most commonly used to describe optic nerve sheath meningioma.
Optic nerve sheath meningiomas often present as segmental or diffuse optic sheath thickening.
When injected with an enhancer, the optic nerve appears as an unenhanced, low-density (signal) line-like structure on CT or MR images, surrounded by surrounding reinforced meningioma.
Produce track-like signs in a cross-sectional or sagittal plane with two tracks of the tumor separated by a low-signal optic nerve.
On the coronal surface, it appears as a bagel-like structure.
When linear calcification occurs in tumors, this sign can also be seen on non-contrasted CT, but is less common than in contrast-enhanced CT.

discuss

Orbital signs are used to distinguish optic gliomas from optic schwan meningiomas.
Optic glioma, regardless of the growth type, is closely connected to the optic nerve, so there is no clear boundary between the tumor and the optic nerve, which is manifested by the homogeneity of the optic nerve-sheath structure, and there is no distinguishable low-density optic nerve structure.

Optic nerve sheath meningioma originates from arachnoid epithelial cells along the optic sheath, grows early under the dura, envelops the optic nerve, does not invade the optic nerve, grows along the optic nerve, and is located in the orbit, in the optic nerve tube, and in the intracranial optic tube opening.

On contrast CT, it shows a) low density of the optic nerve, b) mass-like density of meningioma tissue, and c) parallel line-like high-density enhancement area
adjacent to the optic nerve.

Orbital signs are not specific signs and can also be seen in other intraorbital diseases, such as intraorbital inflammatory pseudotumors, perioptic neuritis, sarcoidosis, leukemia, lymphoma, metastases, perioptic hemorrhage, etc.
, all need to be distinguished by attention.