label: Optic nerve tram-track sign
label_lc: optic nerve tram-track sign
description: "A tram-track sign is composed of two enhancing areas of tumor separated from each other by the negative defect of the optic nerve. It is seen on contrast-enhanced CT scan and MRI images, in optic nerve sheath meningioma. The sign helps distinguish between optic nerve sheath meningioma and optic glioma. Optic glioma arises from glial cells within the optic nerve and there is no clear separation between the nerve and the tumor; hence the tram-track sign is not seen in optic gliomas. Calcification may be seen in optic nerve sheath meningiomas in 20-50% of cases and hence the tram-track sign may be seen on nonenhanced CT scan images as a linear calcification around the nerve, but this is less common."