Optic Nerve Mass

Case A: Images demonstrate enlargement of the left optic nerve sheath with concentric avid enhancement evident on coronal postcontrast images, with a parallel “tram track” appearance to the optic nerve sheath on axial postcontrast images; these features are consistent with an optic nerve meningioma.

Case B: Asymmetric fusiform enlargement of the right optic nerve exhibits subtle contrast enhancement. The appearance of the enlarged nerve indicates a lesion intrinsic to the optic nerve, such as an optic nerve glioma.

Case C: Evidence of the tram track sign, with avid enhancement of the thickened right optic nerve sheath and an intrinsically normal-appearing optic nerve. A broad-based, homogeneously enhancing mass is noted in the left posterior fossa, consistent with an additional meningioma. Precontrast CT does not demonstrate calcification in this case, although homogeneous enhancement and the tram track sign are evident. Incidental note is made of an inferior right orbital schwannoma. Findings are suggestive of neurofibromatosis (NF) type 2 (NF2).