Viral Encephalitis: Imaging Features

Encephalitis commonly referred to as brain fever, implies inflammation of the brain. Since meningeal inflammation often accompanies this inflammatory process, term meningoencephalitis is sometimes used. Symptoms of encephalitis include sudden fever, headache, vomiting, weak muscles, impaired judgement and irritability. Encephalitis is usually caused by viral infection of the brain tissue but can also be caused by other factors such as exposure to certain bacteria, fungi, parasites, harmful chemicals or heavy metal poisoning. Herpes simplex encephalitis (HSE) is the commonest sporadic acute viral encephalitis all over the world. With few exceptions (for example, HSE), no specific therapy is available for most forms of viral encephalitis. The brain damage caused by acute encephalitis is due to a combination of intracellular viral growth and the host inflammatory response. Acute viral encephalitis is caused by direct viral infection of neural cells with associated perivascular inflammation and destruction of gray matter. Acute encephalitis constitutes a medical emergency. Early diagnosis is important for appropriate management. Magnetic resonance imaging of brain is the investigation of choice and the diagnosis may be confirmed by the polymerase chain reaction test for the virus in the cerebrospinal fluid. Mortality and morbidity may be high and long term sequelae are known among survivors. The emergence of some of the zoonotic encephalitis like Japanese encephalitis and Dengu encephalitis have posed an important public health problem in India. Encephalitis resulting from viral infection manifests as either acute viral encephalitis or postinfectious encephalomyelitis. Postinfectious encephalomyelitis follows infection with various viral or bacterial agents; the primary pathologic finding is demyelination of white matter, a non-infective inflammatory encephalitis that may require to be treated with steroids. In emergency cases, the presence of focal neurological signs and focal seizures will distinguish encephalitis from encephalopathy.