Metastatic Melanoma of the Optic Nerve Sheath.

A 23-year-old man with a history of metastatic melanoma developed painful vision loss to counting fingers with enhancement of optic nerve on contrast-enhanced magnetic resonance imaging (MRI) and received a diagnosis of optic neuritis from an outside hospital. Despite empiric corticosteroid therapy, the patient worsened and developed secondary central retinal vein occlusion with further deterioration of vision. Repeat MRI demonstrated optic nerve sheath (ONS) involvement suggestive of optic perineuritis (OPN) and an ONS biopsy confirmed a rare case of isolated metastatic melanoma. Our case highlights the clinical and radiographic features that can mimic OPN and delay diagnosis and treatment.