Optic Neuropathy in Neurosarcoidosis Masquerading as Optic Nerve Sheath Meningioma: A Case Report and Literature Review.

Sarcoidosis is a multisystem granulomatous disorder that often mimics inflammatory, demyelinating, or neoplastic neuro-ophthalmic conditions. We describe a 39-year-old woman with two episodes of progressive visual loss in the right eye over 6 months, with partial responsiveness to steroid. Examination revealed optic disc edema and mild proptosis. Extensive evaluation for demyelinating, autoimmune, infectious, and neoplastic causes was unremarkable. A diagnosis of optic nerve sheath meningioma was initially made at a peripheral center based on the presence of a "tram-track" appearance along the optic nerve sheath on imaging. However, associated orbital fat stranding, lacrimal gland enlargement, and pachymeningeal enhancement prompted further systemic evaluation, which revealed mediastinal lymphadenopathy and omental deposits. Biopsy demonstrated noncaseating granulomas with Schaumann bodies, confirming sarcoidosis after exclusion of alternative granulomatous disorders, including tuberculosis. The patient was treated with immunosuppressive therapy. This case highlights that atypical features, responsiveness to steroid, and extraneural imaging findings should prompt systemic evaluation to enable timely diagnosis and appropriate immunosuppressive therapy.