Ultrastructural study of Rasmussen encephalitis.

Rasmussen encephalitis (RE) is a well-known cause of seizures in children, manifesting histopathology of chronic inflammation of the brain. Its etiology remains unknown. Many reports have suggested the possibility of etiological heterogeneity of this disorder, including the possibility that it is caused by viral infection of the central nervous system, autoimmune phenomena, or a combination of both. The authors report ultrastructural study of 12 cases of RE. They identified most of the features of RE that have been described at the light microscopic level, but did not find any evidence of viral particles, immune complex deposits, or disruption of the blood-brain barrier except in 3 cases: intranuclear (intraneuronal) measle virus-like particles were seen in 1 patient, an electron-dense deposit in the basement membrane of the capillary of another, and a tubuloreticular body in the endothelium of a brain parenchymal capillary in a third (the first 2 rather exceptional findings were previously reported). At present, these appear to be rare findings and not reliable features of RE ultrastructure. The authors also investigated evidence of programmed cell death (apoptosis) of neurons, but only nonspecific degenerative changes of the neurons were found. At present, despite interesting light microscopic and ultrastructural features of RE, its pathogenesis remains cryptogenic.