A) Noncontrast, sagittal T1-weighted magnetic resonance image of the brain of a 67-year-old woman with suspected Powassan virus encephalitis, obtained 4 days after admission. Image is notable for nonspecific signal changes within the thalami, midbrain, cerebellar vermis, and both cerebellar hemispheres. B) Noncontrast, sagittal T1-weighted magnetic resonance image of the brain obtained 8 days after patient's admission. Changes include marked interval progression of signal abnormality involving t
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