Acute Viral Encephalitis Neuroimaging Spectrum

Acute viral encephalitis involves inflammation of the brain caused by multiple different viruses, with CT of the head and MR imaging of the brain involved in the initial diagnostic work-up. Although viral encephalitis may have nonspecific findings on neuroimaging, some imaging patterns have been identified in viral subtypes on MR imaging. The most common cause of encephalitis is herpes simplex virus, with the typical imaging features demonstrating unilateral medial temporal lobe signal abnormalities. Bilateral temporal lobe, cerebellum, and brain stem signal abnormalities are seen in herpes simplex virus 2, with associated edema, necrosis, and hemorrhage. Signal abnormalities are commonly seen in the bilateral basal ganglia, thalami, and mesial temporal lobes in West Nile virus encephalitis. HIV encephalitis is associated with symmetric signal abnormality in the periventricular and deep white matter, which can be differentiated from progressive multifocal leukoencephalopathy by asymmetric U-fiber involvement. The purpose of this article is to present imaging findings associated with typical and atypical cases of viral encephalitis to guide diagnosis, promote early intervention, and improve clinical outcomes.Learning Objective: Identify unique radiologic findings associated with different types of viral encephalitis to guide diagnosis and improve clinical outcomes.