A 50-year-old woman has slowly progressive left visual loss. Contrast-enhanced MRI orbits shows diffuse thickening and enhancement of the left optic nerve sheath with a normal-appearing central nerve, producing parallel lines of enhancement on axial images. Which sign is described and what is the most likely diagnosis?

• A Tram-track sign, optic nerve glioma
• B Tram-track sign, optic nerve sheath meningioma ✓
• C Double vision sign, orbital apex meningioma
• D Target sign, optic neuritis

Explanation

Optic nerve sheath meningioma encases and enhances the sheath while the nerve itself remains unenhanced, giving the tram-track sign on contrast-enhanced axial images, often with associated hyperostosis of adjacent bone. An optic nerve glioma replaces and expands the nerve itself, so enhancement involves the nerve rather than sparing its center, which is the key fact excluding option A. The target sign belongs to neurofibromas elsewhere.

Reference: Som and Curtin Head and Neck Imaging, 5th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.