In acute encephalitis, inflammation

In acute encephalitis, inflammation and edema occur in infected areas throughout the cerebral hemispheres, brain stem, cerebellum, and, occasionally, spinal cord. Petechial hemorrhages may be present in severe infections. Direct viral invasion of the brain usually damages neurons, sometimes producing microscopically visible inclusion bodies. Severe infection, particularly untreated HSV encephalitis, can cause brain hemorrhagic necrosis.

Acute disseminated encephalomyelitis is characterized by multifocal areas of perivenous demyelination and absence of virus in the brain.