A five-year-old otherwise healthy boy presented with a two-week history of behavioral changes, nausea, vomiting, headache, and subacute vision loss bilaterally. Six weeks prior to presentation to our hospital, he had presented to an outside hospital with esotropia and blurred vision in both eyes. At that time, he had bilateral 4+ optic nerve edema. MRI demonstrated a right mesiotemporal lobe arachnoid cyst. Opening pressure on lumbar puncture was elevated, and the patient underwent an arachnoid cyst fenestration. He improved clinically for two weeks but subsequently had a rapid decline in vision and mental status. Repeat MRI showed global enhancement of the leptomeninges, especially of the right mesiotemporal lobe near the arachnoid cyst, and enhancement of both optic nerves and the optic chiasm. Repeat lumbar puncture showed an opening pressure >55cm H2O. He was transferred to our hospital for further care. Initial ophthalmologic examination at our hospital revealed 20/400 visual acuity in the right eye and 20/800 visual acuity in the left eye. Visual fields were constricted to approximately 10-degree nasal islands bilaterally. Motility and alignment were normal. Ophthalmoscopy revealed bilateral 4+ optic disc edema with surrounding peripapillary retinal edema. Given the significant bilateral vision loss, an optic nerve sheath fenestration was attempted, but engorgement of the ophthalmic vessels prevented completion of the procedure. Repeat lumbar puncture showed an opening pressure again of >55cm H2O. An extraventricular drain was placed and dura was biopsied, revealing benign dense connective tissue. An infectious, autoimmune, and paraneoplastic laboratory work-up was unrevealing, and CSF cytology was negative for malignancy and infection. Repeat MRI brain and spine revealed a possible primary tumor involving the right mesiotemporal lobe and hippocampus and multifocal areas of leptomeningeal enhancement outlining the spinal cord conus, raising a question of metastatic disease. Spinal cord arachnoid biopsy was performed, showing histiocytic infiltration with reactive changes. An additional procedure was performed
