Original contributionThe role of histopathologic subtype in the setting of hippocampal sclerosis-associated mesial temporal lobe epilepsy

- The most common hippocampal sclerosis pattern observed was ILAE type Ib.
- The majority of hippocampal sclerosis cases were associated with adjacent focal cortical dysplasia.
- Hippocampal sclerosis subtype does not appear to affect epilepsy surgery outcomes.
- Coexistent focal cortical dysplasia was associated with better postoperative outcomes.

SummaryHippocampal sclerosis (HS) and focal cortical dysplasia (FCD) are among the most common neuropathological findings in those undergoing surgery for refractory mesial temporal lobe epilepsy. Existing data regarding differences among the most recent International League Against Epilepsy (ILAE) HS subtypes remain limited. This study sought to characterize the roles of HS subtype and coexistent FCD. Epilepsy surgery pathologic specimens in 307 cases of temporal lobe epilepsy with HS were reviewed (mean age ± SD, 37 ± 15 years; 56% women). HS and coexistent FCD were classified according to ILAE guidelines. Medical records were reviewed for data on seizure recurrence and seizure burden (clinical follow-up mean duration ± SD, 5 ± 4 years). Cases of typical HS (ILAE type I) predominated (ILAE type Ia: 41%, Ib: 47%, II: 11%, and III: 0.7%]. The HS subtypes shared similar demographic and etiologic characteristics, as well as associated pathology and postoperative seizure outcomes. Individuals with type Ib HS were more likely to remain seizure free at long-term follow-up when compared with other subtypes, and they had a later age of seizure onset. Two hundred forty-three cases (79%) demonstrated FCD within the adjacent temporal lobe. Its presence was associated with a significantly decreased risk of seizure recurrence (P = .02). When present, FCD was predominantly type I (98%). HS subtype does not appear to affect epilepsy surgery outcomes despite some clinical differences between the subgroups. FCD is often observed in association with HS in mesial temporal lobe epilepsy; the finding of FCD was associated with better postoperative outcomes.