Optic nerve sheath meningioma and optic neuropathy: A clinical and diagnosis crossroad.

Optic nerve sheath meningiomas (ONSMs) are rare, benign tumors of the central nervous system that arise from arachnoid cap cells. They most commonly affect middle-aged women and account for approximately 2% of orbital tumors. ONSMs typically present with slowly progressive, painless, ipsilateral optic neuropathy; however, atypical acute or subacute onset may mimic inflammatory optic neuritis. We describe the case of a 45-year-old woman who presented with a 1-month history of progressive visual blurring in the left eye, accompanied by retro-orbital pain and optic disc swelling. Initial clinical and paraclinical findings were suggestive of optic neuritis, and high-dose corticosteroid therapy was initiated, leading to transient improvement. Recurrence of symptoms, lack of sustained steroid response, and magnetic resonance imaging (MRI) findings showing circumferential thickening of the optic nerve sheath with the characteristic "tram-track" appearance on axial views and the "doughnut" sign on coronal sections ultimately led to the diagnosis of ONSM. The patient was managed conservatively with regular ophthalmologic and radiologic follow-up. This case underscores the diagnostic challenge of distinguishing ONSM from inflammatory optic neuropathies and highlights the pivotal role of magnetic resonance imaging (MRI) in confirming the diagnosis, avoiding unnecessary biopsy, and guiding therapeutic decisions.