Temporal lobectomy for intractable epilepsy: Correlation of ictal onset determined by chronic electrocorticography and seizure outcome with degree of hippocampal sclerosis

This study sought to determine whether hippocampal sclerosis (HS) can be predicted from the results of electrocorticography (ECoG). One hundred seven patients underwent anterior temporal lobectomy (ATL) (44 R, 63 L) for epilepsy in the absence of a structural lesion and had the degree of HS graded pathologically from 0 to 4. Preoperative evaluation included ictal chronic ECoG with subdural strip electrodes, which showed a temporal onset in each case. Twenty-seven (25%) specimens were grade 0, 15 (14%) were grade 1-2, and 65 (61%) were grade 3-4. ECoG showed a unilateral mesial temporal seizure onset in 70% of grade 0, 73% of grade 1-2, and 78% of grade 3-4 patients (p > 0.5). A unilateral regional onset, i.e., involving all temporal electrodes, occurred in 15% of grade 0, 13% of grade 1-2, and 12% of grade 3-4, patients (p > 0.5). Bilateral independent onset occurred in 11% of grade 0, 13% of grade 1-2 (p > 0.5), and none of grade 3-4 patients (p < 0.01). We conclude that results of ECoG cannot reliably predict HS. Its use in planning whether mesial structures should be preserved during ATL is therefore limited. With regard to outcome, 1 year after surgery 64% grade 0 patients were seizure-free, 73% grade 1-2, and 78% grade 3-4 (p < 0.05). Results of ECoG were more reliable predictors of outcome. Sixty-five percent of those with unilateral mesial temporal onset were seizure-free at 1 year-50% of those with unilateral regional onset (p < 0.05) and 40% of those with bilateral independent onset (p < 0.001).