Case of the season: dural arteriovenous fistula mimicking a bithalamic neoplasm or viral encephalitis.

A 51-year-old man presented to an outside emergency department with progressive somnolence, memory impairment, and gait instability for 5 weeks, with acute worsening of symptoms 2 days prior to presentation. The patient was a former cigarette smoker, with a history of hypertension and coronary artery disease. He otherwise had no significant medical history. Magnetic resonance imaging (MRI) performed at the outside facility revealed bilateral expansile contrast-enhancing lesions within the thalami. The leading diagnostic considerations were neoplasm or infectious viral encephalitis. The patient was referred to our facility and admitted for further evaluation. On physical examination, the patient was hypertensive (blood pressure1⁄4 175/87), with otherwise normal vital signs. Neurologic examination revealed a flattened affect, a narrow shuffling gait, and cogwheel rigidity in the upper arms. Memory recall was impaired. Right lateral gaze nystagmus was present. The remainder of the examination was normal. Cerebrospinal fluid analysis revealed mild leukocytosis (6.7 white blood cell per high-power field), elevated levels of protein (97.3 mg/dL), and normal level of glucose (58 mg/ dL). The findings of cerebrospinal fluid gram stain, culture, venereal disease research laboratory test, herpes simplex virus polymerase chain reaction, and bacterial antigens were negative. The findings of blood carboxyhemoglobin, serum thiamine, serum Lyme, and antinuclear antibody titers were