Rasmussen encephalitis is a chronic, progressive inflammation of the brain of un-known origin. The onset is in childhood and is characterized by an abrupt appear-ance of focal, persistent motor seizure activity (epilepsia partialis continua), followed by hemiplegia and progressive cognitive deterioration. Early diagnosis and treatment with immunoactive agents or hemispherectomy are sought to prevent the cognitive decline. A hypothesis of the pathogenesis is glutamate receptor autoimmunity associated with persistent viral infection (24). This receptor activation may trigger seizures in these patients.
Histopathologic examination of biopsy material reveals a characteristic triad of findings: perivascular lymphocytic cuffing of round cells, gliosis and microglial nodules. CT and MRI demonstrate progressive destruction of a single cerebral hemisphere (Figure 10). Decreased NAA and elevation of glutamate/glutamine levels on MRS are reported (25).
Figure 10. An 11-year-old girl with Rasmussen encephalitis proven by pathology.
A. T2WI shows mild right hemispheric atrophy.
B. Six years follow-up T2WI shows progression of right hemispheric atrophy.