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Rasmussen encephalitis

Rasmussen encephalitis (RE) (not to be confused with a Rasmussen aneurysm) is a chronic inflammatory disease of unknown origin, usually affecting one brain hemisphere.

Epidemiology

Children of ten years or younger age group are affected in 85% cases1. However, disease detection rate in adults is increasing, with routine MRI investigations in intractable seizure patients5.

Pathology

Pathologic features are similar to viral encephalitis, with lymphocytes around round cells, and diffuse proliferation of microglia. However, later spongiform degeneration and cortical atrophy sets in.

Aetiology

Exact cause of the disease is unknown, however various viral (SSPE like, EBV or CMV), or inflammatory episodes have been implicated by different authors3, 4, 6.

Clinical features

Patients frequently have episodes of epilepsia partialis continua and, much less frequently, generalized status epilepticus. The seizures are intractable despite aggressive medical management 1.

Apart from seizures, patient may have hemiparesis, and speech disturbances, as well as hemianopia (pertaining to unilateral cerebral involvement). Mental deterioration over time may also be seen, especially in patient presenting later in younghood.

Radiographic features

CT

CT may not show any specific feature in early imaging, however patchy hypodense attenuation areas (similar to viral encephalitis) may be seen. Late stage disease may show unilateral cortical atrophy. CT perfusion may show decreased cerebral blood flow (CBF)1.

MRI
  • T1 - unilateral cortical atrophy, with ex-vacuo ventricular dilatation.
  • T2 - hyperintense signal areas in the affected hemisphere.
  • DWI - restricted diffusion may be seen in altered signal areas.
  • T1 C+ (Gd) - no significant post-contrast enhancement.

Treatment and prognosis

Medical treatment in form of anti-epileptics may or may not help during seizure episodes. Usually, disease progresses to intractable and continuous seizures, when surgical treatment in form of hemispherectomy, may be the only option.

Differential diagnosis

General imaging differential considerations include

Etymology

It was first described by T Rasmussen in 1958 2

See also

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