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

Abstract and Introduction


Viral encephalitis is still a life-threatening disease occurring at any age. It is critical to make a rapid and correct diagnosis for a better outcome of the disease. Accumulating evidence has suggested that MRI is a powerful tool for the detection of any lesion of the CNS caused by viral infections and helps to initiate the timely treatment. In this review, we summarize the current understanding of MRI findings of viral encephalitis, especially related to HSV, HIV, varicella zoster, Japanese encephalitis, John Cunningham, and influenza viruses. With these considerations, we learnt that the inclusion of diffusion-weighted image sequences on routine MRI examination would have a significant value in detecting the pathologic changes that occur following viral invasion of the CNS.


Viral encephalitis is a life-threatening disease that can occur at any age. The most common virus causing encephalitis in humans is HSV. In recent years, however, the incidence of infection with HIV has abruptly increased in Japan. This increasing incidence of HIV infection has also increased the frequency of HIV-associated encephalopathy and concomitant opportunistic infections of the CNS. Previous studies have shown that persistent viral infection of the CNS by HIV results in structural alterations that are detectable by MRI.[1–4] These studies have permitted the identification of individuals at risk of developing CNS abnormalities and have helped the initiation of the early treatment. Thus, MRI is now widely accepted as a sensitive technique for the diagnosis of various kinds of encephalitis and is very useful for detecting early changes caused by viral infection.[5]

Here, we will summarize the current achievements of neuroimaging studies of various kinds of viral encephalitis and discuss the most reliable methods for the evaluation of the disease. In the present manuscript, we will focus on encephalitis caused by HSV, HIV and varicella zoster virus (VZV) and describe the most recent understanding of the findings of neuroimaging studies on viral encephalitis.