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Mesial temporal sclerosis and temporal lobe epilepsy

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Mesial temporal sclerosis is the most common lesion found in adults with temporal lobe epilepsy. For many years it has been held that these lesions may be related to complicated febrile convulsions in childhood but the association is based on retrospective data and a cause-and-effect relationship has not been proved. A magnetic resonance imaging (MRI) follow up study of children after febrile convulsions (

) has shown no evidence of mesial temporal sclerosis.

From a total of 329 children with febrile convulsions 64 were selected for study; 24 who had had a prolonged (30 minutes or more) convulsion, 8 who had had at least one unprovoked seizure on follow up, and 32 controls who had had a single simple febrile convulsion (short (15 minutes or less), non focal, and not repeated within the episode). MRI scans were performed after a mean follow up of 12.3 years. No patient had mesial temporal sclerosis and the volumes of right and left hippocampal formations and amygdala were similar in the three groups. A lower mean difference in volume between right and left hippocampal formations in the prolonged febrile convulsion group was not thought to be clinically significant. These researchers conclude that mesial temporal sclerosis is not a common sequel of even prolonged febrile convulsions and they believe that there is no causal relationship between the two.

On the other hand, mesial temporal sclerosis is common in children with severe temporal lobe epilepsy. In Montreal (

) the neuropathology was reviewed of 22 children who had undergone anterior temporal lobectomy for refractory temporal lobe epilepsy during a 20 year period (1979–99). Fourteen of the 22 temporal lobes had cortical dysplasia (CD) of the neocortex and mesial temporal sclerosis was present in 12 of 15 specimens with available hippocampal tissue. Seven children had both kinds of lesion. The importance of dual pathology (mesial temporal sclerosis plus an extra-hippocampal lesion) in patients with severe temporal lobe epilepsy is increasingly recognised as are the clinical differences between paediatric and adult temporal lobe epilepsy. (Children describe fewer auras, have simpler automatisms, and more frequent motor manifestations, mostly tonic.)

The relationship between prolonged febrile convulsions and later mesial temporal sclerosis is questionable and temporal lobe epilepsy in children may be a different entity from temporal lobe epilepsy in adults.