Rasmussen’s encephalitis is a rare progressive seizure disorder of unknown aetiology, commonly presenting in childhood. It begins with partial motor seizures, secondary generalised seizures or epilepsia partialis continua and is associated with neurological deficits and unilateral hemispheric atrophy. The macroscopic brain changes are subtle and predominantly unilateral and include cerebral atrophy and mildly discoloured cortex. The histology in early stages shows an inflammatory process consisting of mainly T lymphocytes around blood vessels, microglial reaction and neuronophagia. These features are similar to those seen in viral encephalitis which needs to be excluded by appropriate tests. At a later stage, there is pan-cortical neuronal loss, gliosis and spongiosis with minimal inflammation. The inflammatory process is multifocal, patchy, and although unilateral in most cases, occasional post-mortem cases with bilateral pathology have been described. There is no convincing evidence of an infectious aetiology [1] and some evidence suggests that this represents an immunological disease [2]. There can be associated lesions such as focal cortical dysplasia, vascular malformation, and tumours. Early treatment with immunosuppression or surgery (hemispherectomy) may be effective in slowing the disease progression and controlling seizures.

Focal cortical dysplasia (FCD) represents a malformative lesion arising from an abnormal cortical development (the term ‘dysplasia’ in this context should not be mistaken for a premalignant condition). FCD is frequently associated with epilepsy (usually refractory to drugs), in both children and adults. The lesions are commonly located within the frontal or temporal lobes and may be visible as focally thickened cortex or blurred grey-white matter junction on naked eye inspection. The International League Against Epilepsy (ILAE) task force has introduced a three-tiered consensus classification system based largely on neuropathological features (Table 8.2) [3].