QUIZ: No. 15, 15/06/2025

ANS – Right oculomotor nerve sheath meningioma at the orbital apex.

DD : Orbital apex meningioma with mass effect on CN III

Findings: Well-defined extra-axial lesion at the right orbital apex, along the expected course of the right oculomotor nerve. The lesion appears isointense on T1WI, hypointense on T2WI and FLAIR sequences, with homogeneous and avid contrast enhancement on post-contrast T1WI. There is no evidence of diffusion restriction on DWI/ADC sequences. The lesion is located lateral to the optic nerve, exerting mild mass effect, without signs of bony erosion. There is mild atrophy of the EOM supplied by CN III.

Take home points

·       Oculomotor nerve meningiomas can present with isolated third nerve palsy symptoms. Imaging clues include a homogeneously enhancing lesion at the orbital apex with close relation to the oculomotor nerve.