Abstract
A 49-year-old previously healthy woman presented with acute painless visual loss in the right eye, a right relative afferent pupillary defect, and a normal fundus examination. She was diagnosed with retrobulbar "optic neuritis" and given a course of intravenous steroids. Despite treatment, however, she continued to lose vision and serial visual field testing confirmed a junctional scotoma in the fellow eye. Cranial magnetic resonance imaging (MRI) showed a mass at the junction between the right optic nerve and the anterior aspect of the chiasm and a right frontal lesion that proved to be multicentric glioblastoma multiforme. Clinicians should be aware of the possibility of aggressive neoplasm in the differential diagnosis of retrobulbar optic neuritis.