An Update on Diagnostic Imaging Studies for Viral Encephalitis

Naoki Kawamura; Madoka Kizawa; Akihiro Ueda; Yoshiki Niimi; Tatsuro Mutoh


Future Virology. 2012;7(9):901-909. 

In This Article

Other Characteristic MRI Findings From Virus-related Infections

Japanese Encephalitis Virus

Japanese encephalitis virus has affinity to thalami of the brain. Therefore, typical cases of this viral infection showed bilateral thalamic involvement on both T2-W and FLAIR MRI sequences.[27] The Japanese encephalitis virus can invade the CNS by way of the hematogenous route, and subsequent spreading occurs along the dendritic axons not only to the thalami but also to the basal ganglia, brain stem, cerebellum and cortical areas of the brain. Typical lesions on brain MRI show as hyperintense on T2-W images and hypointense on T1-W images (Table 1).

JC Virus

JC virus is the virus responsible for the development of progressive multifocal leukoencephalopathy. Progressive multifocal leukoencephalopathy is a demyelinating disease caused by the reactivation of JC virus in immunocompromised patients. In this disorder, the lesions are hypointense on T1-W and hyperintense on T2-W imaging compared with normal white matter.[28] The involvement is most often asymmetric, with relative sparing of the periventricular white matter. Involvement of parieto-occipital white matter and the corpus callosum is often observed in most patients with this disorder (Table 1).

Influenza Virus

Influenza virus encephalitis is a rare complication of infection with this virus. We recently found a patient with H1N1 influenza virus encephalitis who showed a hyperintense lesion on DWI sequence in the splenium of corpus callosum, which disappeared with treatment.[29] The presence of a hyperintense splenial lesion seems to be a useful indicator for a good prognosis in this disorder (Table 1).[29]


In childhood, many individuals may suffer from chickenpox, of which the causative virus is VZV. CNS complications of acute infection of VZV include aseptic meningitis, leukoencephalopathy, vasculopathy, dorsal root or cranial nerve ganglionitis, polyradiculoneuritis, ventriculitis, necrotizing angitis and meningoencephalitis. Postherpetic neuralgia, vaculopathy and retinal necrosis are the most serious complications of VZV reactivation. Neuroimaging studies have shown abnormalities such as abnormal signal intensity and swelling of the cerebral cortex, basal ganglia, cortical–white matter junction or cerebellum. In some cases, they exhibit plexitis or radiculitis, thickening of the nerve roots with significant post-contrast enhancement (Table 1).[30]

Dengue Virus

Dengue virus is a RNA arbovirus and serologically exists in four different types. Serological types 2 and 3 usually affect the CNS, causing encephalitis and myelitis. Previous patients in the literature have exhibited encephalitis (general cerebral edema) and focal abnormalities involving the basal ganglia, hippocampus and thalami, pontine hemorrhage, and even acute disseminated encephalomyelitis.[31] Brain lesions associated with this virus showed mixed hyperintensity on T2-W and FLAIR sequences, with hypointensity on T1-W imaging.