Here we describe a rare case of optic nerve sheath meningioma (ONSM) which was previously mistaken for optic neuritis.

A 48-year-old woman presented to the emergency department with left eye pain. She has had 4 worsening episodes over the last 25 years of left eye pain which were treated as optic neuritis and idiopathic orbital inflammatory disease (IOI) with corticosteroids during each episode. On exam, her visual acuity was 20/25 right eye (OD), counting fingers left eye (OS) with relative afferent pupillary defect (RAPD) OS. Fundus examination showed normal optic disc OD and optic disc pallor OS. Magnetic resonance imaging (MRI) of orbits was consistent with optic nerve sheath meningioma with extension to left optic canal and extending along the posterior wall of the sphenoid sinus and left anterior clinoid process. Over the next 4 months visual acuity in the left eye progressively decreased likely due to optic nerve compression. Due to the rapid progression and symptomatic nature of the tumor, patient underwent left sided pterional craniotomy for sub frontal approach for resection of tuberculum sella meningioma, extensive decompression of the optic nerve and canal.

Our case highlights the difficulty in diagnosing ONSM when presented with acute visual loss in association with painful eye movements mimicking optic neuritis. Lack of recovery or progressive loss of vision should prompt the clinician to explore alternative diagnoses other than typical demyelinating optic neuritis. Finally selecting the appropriate imaging protocol in the setting of progressive loss of vision, particularly high-resolution contrast MRI of the orbit with fat-suppression sequences, can be crucial in making the correct diagnosis.