INCREASED NEOCORTICAL SPIKING AND SURGICAL OUTCOME AFTER SELECTIVE AMYGDALO-HIPPOCAMPECTOMY

We studied the electrocorticogram (ECoG) before and immediately after transcortical selective amygdalo-hippocampectomy, prospectively in 13 consecutive patients and retrospectively in three others. ECoG was per formed with surface and two depth electrodes inserted through T2 aimed at the amygdala and anterior hippocampus. Before resection the ECoG s howed a variable amount of interictal spiking, recorded either indepen dently from the depth and surface, or synchronously. A small cortical incision (2-3 cm) was made in T2. The hippocampus, amygdala and parahi ppocampal gyrus were removed subpially. After the resection, increased epileptiform abnormality was observed in all 16 patients and a differ ent ECoG pattern emerged. It consisted of repetitive, high amplitude s pikes and polyspikes, separated by attenuated background, recorded fro m the most anterior temporal area. Similar observations were reported by Niemeyer in 1958. The outcome was comparable to that of standard an terior temporal resection: 62.5% class I and 25% class II (Engel's sca le). ECoG is often used to tailor the amount of resection, and the per sistence of epileptic abnormalities correlates with worse outcome. Thi s is not the case in selective amygdalo-hippocampectomy, suggesting th at a different underlying mechanism is responsible for the increased i nterictal spiking following this procedure.