Abstracts

Rationale: Unilateral hippocampal atrophy is associated with an excellent surgical outcome after temporal lobectomy. The management of patients with bitemporal hippocampal atrophy is more controversial and many undergo intracranial EEG (iEEG) and deemed poor surgical candidates. The purpose of this study is to investigate the correlation of surgical outcome with intracranial monitoring and quantitative hippocampal volumetry in patients with bilateral hippocampal atrophy.Methods: Volumetric hippocampal analysis was performed on the MRIs of consecutive drug resistant temporal lobe epilepsy patients between the ages of 16 and 45 years who underwent bitemporal depth electrode recording at our institution from 1994 to 2007. The hippocampal volumes were compared to age matched controls, and significant atrophy defined as greater than two standard deviation difference from control. Symmetric hippocampal atrophy was defined by a difference between the right and left hippocampus between the range 0.1 and + 0.3 cm3, otherwise the patients were defined as asymmetric hippocampal atrophy. The localization of ictal and interictal discharges on scalp and iEEG were reviewed, and surgical outcome determined for each patient.Results: Of the 52 patients with bilateral hippocampal atrophy, 30 had symmetric and 22 had asymmetric hippocampal volumes. The surgical outcome was available for 33 patients with an average follow up of 42 months. Fourteen of 15 surgical patients with asymmetric atrophy (93%) had an Engel class 1 outcome. All of these 14 patients with a favorable outcome had most significant atrophy on the resected side. Additionally, predominant side of seizure onset on iEEG was concordant with asymmetric smaller hippocampus in almost all patients (14/15) with significant atrophy. On the other hand, nine of 18 surgical patients with symmetric hippocampal atrophy (50%) who underwent resection of the predominant side of seizure onset on iEEG had favorable outcomes, while seven of them had an Engel class 1 outcome. The asymmetric hippocampal atrophy group had better surgery outcome than symmetric hippocampal atrophy group (P<0.01) Conclusions: In this retrospective study, patients with significant asymmetric hippocampal atrophy had a high probability (93%) of seizure free outcome. The smaller hippocampus was concordant with the predominant side of iEEG seizure onset in all patients with significant asymmetric atrophy. On the other hand, only 50% of patients with symmetric hippocampal atrophy had favorable surgical outcomes. We found that iEEG recordings and quantitative hippocampal volumes are useful for localization of epileptogenic brain and selection of surgical candidates. The patients with asymmetrical hippocampal atrophy are potentially good surgical candidates, while patients with symmetric atrophy had less chance of excellent outcome.