Section Editor: Sandy Cheng-Yu Chen, M.D.
Taipei Medical University Hospital, Taipei, Taiwan
West Nile virus (WNV) is a mosquito-borne flavivirus that can infect humans. Neuroinvasive WNV can manifest as encephalitis, meningitis, and/or myelitis. Classic MR imaging features of WNV encephalitis include T2/FLAIR hyperintensities in the thalami (A, arrows), basal ganglia, tegmentum/brainstem (B, arrows), and cerebellum. Diffusion restriction may be seen in the affected regions and the cerebral white matter (C, arrows). CSF PCR analysis of WNV RNA was diagnostic of West Nile encephalitis. Bilateral thalamic lesions carry an important differential diagnosis including vascular, toxic/metabolic, and neoplastic etiologies. In the setting of viral prodrome and appropriate environmental factors, WNV should be considered.