Thursday 21 September 2017

Japanese encephalitis MRI

Clinical Details : fever with seizures, loss of consciousness.
Clinically no history of poisoning or primarily metabolic derangement.

This MRI study of brain FLAIR and Diffusion shows abnormal T2 hyperintensity with marked parenchymal swelling, bilateral and Symmetrically involving thalami, Pons, bilateral cerebellar hemisphere with restricted diffusion. Confluent T2 hyperintensity Bilateral Symmetrically involving fronto parietal Peri ventricular white matter.
Oedematous thalami causing Third ventricle compression leading to mild dilatation of lateral ventricles. Diffuse cerebral oedema.
Normal MR venography of brain.

Imaging wise differential diagnosis:
Viral encephalitis Japanese encephalitis
Toxic/Metabolic leukoencephalopathy.

Japanese encephalitis

Causative agent is Japanese encephalitis virus , a single-stranded RNA flavivirus.
Domestic pigs and wild birds are reservoirs for the virus, spreads by mosquitoes. Disease is prevalent in India, South East Asia.

Clinical presentation is usually rigors, fevers and headache.
Neck rigidity, cachexia, hemiparesis and convulsions as signs of meningitis as disease progresses.

Bilateral thalamic involvement is classical as hypodensities on CT and T2 hyperintensities on MRI with restricted diffusion, marked a focal parenchymal swelling. Associated midbrain, pons, cerebellum, basal ganglia, cerebral cortex and spinal cord involvement is well known. Imaging after 3-4 days of the onset may reveal haemorrhage giving rise to low signal intensity haemosiderin staining on GRE.

Treatment is only supportive with higher mortality rate. Vaccination may be preventive in endemic areas.

Differential diagnosis
Other infectious causes that can cause a similar imaging pattern are Murray Valley encephalitis, West Nile fever, eastern equine encephalitis, herpes simplex encephalitis.
However in Herpes which is promptly treatable with antivirus treatment, the medial temporal lobe involvement is classical with uncommon thalamic involvement.
Bilateral thalamic haemorrhage in Japanese encephalitis is often confused with deep cerebral vein thrombosis. So it is important to run MR venography to demonstrate normal straight sinus.

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