25 year-old man noticed slow progressive decrease in vision in left eye. Vision was 20/20 OD and 20/40 OS, there was swelling of left optic nerve head. MRI demonstrated white matter lesions in left frontal lobe; cerebrospinal fluid composition was normal. Patient was seen in MS clinic and treatment with dimethyl fumarate commenced. Vision continued to deteriorate and when seen by neuro-ophthalmology service 4 months later it was 20/200 in affected eye with brisk left RAPD and dramatically swollen left optic nerve head. Urgent MRV was interpreted as normal and MRI demonstrated white matter changes in deep left frontal lobe, felt to be microischemic, not demyelinating. Dimethyl fumarate was discontinued; serological workup (HIV, Lyme, Toxoplasma, Bartonella, VDRL, ACE, ANA, ds-DNA, ENA and NMO testing) was unrevealing. CT body was normal. Vision remained stable. Dramatic swelling of left optic nerve persisted as he was followed over 2 years. 2.5 years after initial presentation the patient experienced sudden seizure. MRI demonstrated mass lesion surrounded by edema in left frontal lobe. After transfer to our center biopsy of the lesion was interpreted as "indeterminate" but negative for neoplasm. Second opinion on the biopsy commented on findings inconsistent with both demyelination and arterial infarct. Cerebral Angiography (angiogram) reported unusual tortuous left hemispheric cortical veins without arteriovenous shunting lesion. After extensive multidisciplinary consultation, neurosarcoidosis was felt to be a unifying diagnosis despite absence of tissue diagnosis proving it. Treatment with intravenous methylprednisolone and mycophenolate commenced. MRI done 2 months after starting immunosuppression demonstrated dramatic resolution of the left frontal lobe lesion. Unsatisfied with the diagnosis, all neuro-imaging was re-reviewed. On angiogram the unusual tortuous cortical veins in the left hemisphere were reminiscent of the "pseudophlebitic pattern" seen with brain dural AV fistula (BDAVF). Diagnostic procedure was performed
