Viral Encephalitis Imaging Characteristics

Viral encephalitis presents distinct imaging features depending on the specific type of virus involved. These characteristics are essential for accurate diagnosis and effective treatment planning. Below is a detailed overview of the most common forms of viral encephalitis and their associated imaging findings:

Herpes Simplex Virus (HSV) Encephalitis

Herpes simplex virus encephalitis is one of the most clinically significant and recognizable forms of viral brain infection. It typically affects the temporal lobes and hippocampal regions, either unilaterally or bilaterally. On head CT scans, early signs may include hypodense lesions in these areas accompanied by edema. Due to the high risk of hemorrhage, mixed hyperdense regions may also be observed. In MRI imaging, lesions often appear as iso- or hypointense on T1-weighted sequences and hyperintense on T2-weighted sequences. In cases of prominent cytotoxic edema, diffusion-weighted imaging (DWI) can reveal bright hyperintense signals, further supporting the diagnosis.

Varicella-Zoster Virus (VZV) Encephalitis

Varicella-zoster virus encephalitis can involve the brain, spinal cord, and nerve roots. In mild cases, no visible abnormalities may appear on imaging. However, as the disease progresses, localized cerebral edema and reduced tissue density may become apparent. These changes can be detected through both CT and MRI, particularly in the later stages of infection. MRI is often more sensitive in identifying subtle inflammatory changes and demyelination associated with VZV-related encephalitis.

Cytomegalovirus (CMV) Encephalitis

Cytomegalovirus encephalitis predominantly affects the periventricular regions of the brain. Imaging typically reveals periventricular demyelination or "periventricular dropout" patterns. On CT scans, these lesions appear as hypodense areas surrounding the ventricles. In MRI studies, T1-weighted images may show slightly hypointense signals around the ventricles, while T2-weighted sequences highlight these regions as hyperintense, indicating widespread inflammation and damage to the surrounding white matter.