Thursday 21 September 2017

Giant Tumefactive Perivascular Spaces MRI

Clinical Details: headache.
MRI brain with Contrast

MRI study of brain with contrast shows a well defined, multilocular cystic lesion isointense to CSF, non-enhancing on post contrast involving left thalamus, adjacent mesencephalic mid brain. An associated mild mass effect causing third ventricle compression however no obvious obstructive hydrocephalus. No obvious low signal intensity haemosiderin staining on GRE. No obvious adjacent perilesional oedema on FLAIR.

Imaging findings suggestive of giant Tumefactive Peri vascular space – a benign non-tumoural cyst.
Suggested follow-up imaging for mass effect.

Giant Tumefactive Perivascular Spaces

Perivascular spaces (PVSs) are pial-lined, interstitial fluid-filled structures that accompany penetrating arteries, also known as Virchow-Robin spaces when enlarged, they may cause mass effect and can be mistaken for various ominous pathologic processes.
Often appear as clusters of variably sized cysts that are isointense to CSF on all pulse sequences and do not enhance, Gaint Tumefactive VR spaces assuming bizarre configurations with striking mass effect should not be mistaken for neoplasm.
They are most common in the mesencephalo thalamic region and may cause hydrocephalus.

Reference: Giant Tumefactive Perivascular Spaces Karen L. Salzman, Anne G. Osborn, Paul House, J. Randy Jinkins, Adam Ditchfield, James A. Cooper and Roy O. Weller
American Journal of Neuroradiology February 2005, 26 (2) 298-305

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.