Physical Address

304 North Cardinal St.
Dorchester Center, MA 02124

Miscellaneous Encephalitis


KEY FACTS

Terminology

  • Diffuse brain parenchymal inflammation caused by variety of pathogens, most commonly viruses

  • Location dependent on etiology

Imaging

  • Abnormal T2 hyperintensity of gray matter ± white matter or deep gray nuclei

  • Large, poorly delineated areas of involvement common, ± patchy hemorrhage

  • Imaging is often nonspecific, mimics other etiologies

Top Differential Diagnoses

  • Acute ischemia

  • Autoimmune encephalitis

  • Herpes encephalitis

  • Status epilepticus

  • Toxic/metabolic lesions

Pathology

  • Most (but not all) are caused by viruses

  • Spread of virus to CNS is hematogenous or neural

Clinical Issues

  • Herpes: Most common cause of sporadic (nonepidemic) viral encephalitis

  • Japanese encephalitis: Most common endemic encephalitis in Asia

  • Many encephalitides have high morbidity, mortality

  • Rapid diagnosis and early treatment with antiviral or antibacterial agents can decrease mortality, may improve outcome

Diagnostic Checklist

  • Clinical history often helpful for accurate diagnosis

  • DWI may detect lesions earlier than conventional MR

Axial FLAIR MR shows hyperintense signal primarily in the left posterior frontal lobe
in an immunosuppressed patient with CMV meningoencephalitis. CMV typically involves the periventricular white matter.

Axial DWI MR in the same patient shows restricted diffusion in the left posterior frontal lobe
with involvement of the gray and white matter. DWI is often positive in encephalitis and may be the most sensitive MR sequence.

Axial FLAIR MR shows symmetric abnormal hyperintensity in the basal ganglia
and thalami in this patient with West Nile virus encephalitis. Symmetric appearance of deep gray nuclei involvement mimics toxic and metabolic etiologies.

Axial FLAIR MR in a patient with ataxia shows diffuse hyperintensity and enlargement of brainstem
. Rhombencephalitis is often caused by viruses; other pathogens include Listeria monocytogenes, Legionnaire, Mycoplasma, Lyme disease.

TERMINOLOGY

Definitions

  • Diffuse brain parenchymal inflammation caused by variety of pathogens, most commonly viruses

  • Location dependent on etiology

IMAGING

General Features

  • Best diagnostic clue

    • Abnormal T2 hyperintensity of gray matter (GM) ± white matter (WM) or deep gray nuclei

    • Large, poorly delineated areas of involvement common, ± patchy hemorrhage

    • Imaging is often nonspecific

  • Location

    • Herpes simplex virus type 1 ( HSV1 ): Limbic system

    • Cytomegalovirus ( CMV ): Deep periventricular WM

    • Epstein-Barr virus ( EBV )

      • –

        Multifocal, diffuse involvement of brain and spinal cord

      • –

        Splenium of corpus callosum

    • Varicella-zoster virus ( VZV )

      • –

        Varicella: May affect multifocal areas of cortex

      • –

        Zoster: Brainstem/cortical GM, cranial nerves

    • Cerebellitis : Bilateral cerebellar hemispheres

    • Eastern equine encephalitis ( EEE ): BG and thalami

    • Enteroviral encephalomyelitis

      • –

        Enterovirus (EV) 71 : Posterior medulla, pons, midbrain, dentate nuclei, spinal cord

      • –

        Polio, Coxsackie : Midbrain, anterior spinal cord

    • Hantavirus : Pituitary gland hemorrhage

    • HIV-1 : Cerebral WM, brainstem, thalamus, BG

    • Japanese encephalitis : Bilateral thalami, brainstem, cerebellum, spinal cord, cerebral cortex

    • Murray Valley encephalitis ( MVE ): Bilateral thalami; may affect midbrain, cervical spinal cord

    • Nipah viral encephalitis : Multifocal WM

    • Rabies encephalitis : Brainstem, hippocampi, hypothalamus, WM, GM

    • Rhombencephalitis : Brainstem and cerebellum

    • St. Louis encephalitis : Substantia nigra

    • West Nile virus ( WNV ): BG &/or thalami; may affect brainstem, cerebral WM, substantia nigra, cerebellum, spinal cord

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here

Related Posts