Abstracts

Unilateral hippocampal atrophy is associated with an excellent surgical outcome after temporal lobectomy. The management of patients with bitemporal disease is more controversial and many undergo intracranial EEG (iEEG) with bitemporal depth electrodes. The purpose of this study is to evaluate the usefulness of intracranial monitoring for predicting surgical outcomes in patients with both asymmetric and symmetric hippocampal volumes., Volumetric hippocampal analysis was performed on the MRIs of all consecutive intractable temporal lobe epilepsy patients between the ages of 16 and 45 years who underwent bitemporal depth electrode recording at our institution over a seven year period. Symmetric hippocampal volumes were defined by a difference between the right and left hippocampus between the range [ndash] 0.1 and + 0.3 cm³. The hippocampal volumes were compared to age matched controls, and significant atrophy defined as greater than two standard deviation difference from control. The localization of ictal and interictal discharges on scalp and iEEG were reviewed, and surgical outcome determined for each patient., Of the 27 patients, 14 had asymmetric and 13 had symmetric hippocampal volumes. The surgical outcome was available for 22 patients (four did not have surgery and one was lost to follow up) with an average follow up of 51 months.
Ten of 12 surgical patients with asymmetric atrophy (83%) had an Engel class 1 outcome. Nine of these patients with a favorable outcome had significant atrophy on the resected side. The predominant side of seizure onset during iEEG was concordant with the smaller hippocampus in all patients who had significant atrophy.
Four out of ten surgical patients with symmetric atrophy (40%) had a favorable outcome. The degree of atrophy did not predict surgical outcome. Two of the patients with a favorable outcome (50%) and three of the patients with an unfavorable outcome (50%) had significant bilateral atrophy. Of the four patients who had a favorable surgical outcome, three had a predominance of seizures arising from the resected side during iEEG, and three of the patients who had unfavorable outcomes also had a predominance of seizures from the resected side., In this limited retrospective study, patients with asymmetric hippocampal atrophy had a high probability (83%) of seizure free outcome. The smaller hippocampus was concordant with the predominant side of iEEG seizure onset in all patients with significant asymmetric atrophy. Conversely, only 40% of patients with symmetric hippocampal atrophy had favorable surgical outcomes, and iEEG did not prove helpful for predicting outcome.,