A 55-year-old white woman presented with 1 week of decreased visual acuity and ache on abduction in the right eye. She had decreased right-sided hearing and tinnitus, a moderate right-sided frontal headache, and an unsteady gait. She did not have diplopia, facial numbness, or paresthesias. She had a history of stage IV breast cancer treated with letrozole after a mastectomy 5 years prior. On an initial examination, her best-corrected visual acuity was 20/50 OD and 20/25 OS, with dyschromatopsia, relative afferent pupillary defect, and visual-field defects on the right side. Her extraocular movements were full. A dilated fundus examination demonstrated a pale right optic nerve. Magnetic resonance imaging (MRI) of the brain was reported to have normal results, but on review, we noted thickening and enhancement of both optic nerves (with the right eye larger than the left eye) (Figure 1A), cranial nerve III in the right eye, cranial nerve V bilaterally, the pituitary infundibulum, and the hypothalamus, as well as adjacent cavernous sinuses. Leptomeningeal thickening over the convexities of the anterior frontal lobes was also evident (Figure 1B). The patient’s cerebrospinal fluid contained a small population of polyclonal CD19+ B cells and CD4+ and CD8+ T cells. An extensive laboratory workup, including tests for HIV, antinuclear antibodies, anti–double-stranded DNA, antineutrophil cytoplasmic antibodies, serum protein electrophoresis, erythrocyte sedimentation rate, C-reactive protein, complete blood cell count, antiganglioside antibodies, anti–myelin-associated glycoprotein antibodies, and angiotensin-converting enzyme, gave normal results. A computed tomographic (CT) scan of the thorax and a whole-body positron emission tomography (PET)/CT scan revealed no abnormalities.