Seizure outcome following standard temporal lobectomy: correlation with hippocampal neuron loss and extrahippocampal pathology

Abstract

The authors reviewed 149 patients who underwent standard anterior temporal lobectomies for intractable complex partial epilepsy with a mean follow-up period of 5 years. Quantitative analyses of hippocampal neuron loss showed that all patients had some cell loss compared to control hippocampi obtained at autopsy. The average hippocampal cell loss was categorized as severe (greater than 30% of autopsy control levels) or mild. Analysis of hippocampal and extrahippocampal pathologies showed that in 109 cases (73%, the hippocampal lesion group) hippocampal cell loss was mild in 17 cases (16%) and severe in 92 cases (84%); in the remaining 40 cases (27%, the extrahippocampal structural lesion group) hippocampal cell loss was mild in 24 cases (60%) and severe in 16 (40%). The first index of surgical outcome was worthwhile seizure reduction, which occurred in 94 cases (86%) with mild or severe hippocampal lesions and in 33 cases (82%) with extrahippocampal pathology. In the hippocampal lesion group, worthwhile seizure reduction occurred in 90% of cases with severe and in only 65% of cases with mild hippocampal cell loss (p = 0.015). In the extrahippocampal pathology group, worthwhile seizure was not statistically different, whether hippocampal cell loss was severe (94% of cases) or mild (75% of cases). The second index of surgical outcome was the occurrence of residual seizures in the patients with worthwhile seizure reduction, which would indicate remaining epileptogenic tissue. In the hippocampal lesion group, the incidence of residual seizures was not statistically different whether hippocampal cell loss was severe (24% of cases) or mild (45% of cases). However, in the extrahippocampal pathology group, residual seizures occurred in 53% of cases with severe cell loss (dual pathology) but in only 11% of cases with mild cell loss (p = 0.025). Worthwhile seizure reduction can be predicted by the presence of either severe hippocampal cell loss or an extrahippocampal structural lesion. However, residual seizures more frequently follow in cases with a combination of both (extrahippocampal pathology associated with severe hippocampal cell loss, or dual pathology), suggesting that epileptogenic tissue more likely extends outside the boundaries of a standard temporal lobectomy.