Hippocampal sclerosis and a second focal lesion--how often is it ipsilateral?

Hippocampal sclerosis (HS) is the most common pathologic finding in intractable temporal lobe epilepsy (TLE). In many patients, HS is accompanied by an extrahippocampal lesion (EHL). We sought to assess the lobar distribution and side of EHLs in relation to HS in a large consecutive series of patients presenting to our epilepsy surgery program.

The inclusion criterion was the presence of both definite HS and an unequivocal EHL on magnetic resonance imaging (MRI) studies in patients evaluated for potential epilepsy surgery at our tertiary epilepsy center.

Fifty-eight patients were identified over a 7-year period. This represented about one-third of all patients with HS. The mean age was 32 years (SD 18.4), and the mean age of seizure onset 13 years (SD 16.4). Fifty-four percent of the EHLs could be classified as acquired and 36% as developmental. In 98% of patients HS was found on the same side as EHL.

Our findings support the hypothesis that HS may be a secondary event from seizures generated initially by another focal lesion. However, HS and EHL may also originate from the same insult to the brain.