"X" Marks the Spot

This 24 year-old man presented with several months of progressive visual loss in both eyes. His past medical, surgical and ocular history was unremarkable. There was no family history of phacomatosis. He complained of occasional binocular diplopia, but denied headaches or any other neurological symptoms. He denied galactorrhea, fatigue, and abdominal pain. On exam, his visual acuity was 20/125 OD and 20/50 OS. He had incomplete atypical bitemporal defects that respected the vertical meridian and pallor of both optic nerves, right more than left. Magnetic resonance imaging (MRI) of the brain showed an enlarged optic chiasm and a hyperintense left frontal periventricular lesion that was abutting the genu of the corpus callosum. Both lesions showed mild contrast enhancement. The differential diagnosis included a primary intrinsic chiasmal glioma versus an inflammatory etiology. An extensive infectious, inflammatory, and rheumatologic work-up was unrevealing. Cerebrospinal fluid (CSF) evaluation showed a mild lymphocytic pleocytosis (11/mL) and mildly increased protein concentration (54 mg/dL). The CSF showed 3 oligoclonal bands. CSF cytology and cultures were negative. Based on these findings, he received a 1-month course of high dose steroid treatment without clinical improvement and further visual loss in both eyes. Repeat MRI brain showed no radiological improvement. At this point, the patient started complaining of increased thirst. A diagnostic procedure was performed