Abstracts

Rationale: Amygdalohippocampectomy (AHP) has been widely applied for medically refractory temporal lobe epilepsy (TLE). However, its indication for the verbal dominant hemisphere is limited due to the possibility of postoperative memory impairment. To prevent this disabling complication, methods with strong predictive power are highly required. Based on our preliminary experience, we describe the efficacy of provocative test by electrical stimulation of the entorhinal area in preventing postoperative memory impairment. Methods: We performed the abovementioned provocative test on ten consecutive patients with medically refractory TLE involving the dominant hemisphere. Prior to AHP, depth electrodes were inserted to the entorhinal area with stereotaxic technique. During the provocative test, verbal and visual memory functions were evaluated with delayed recall and/or recognition tasks. Electrical stimulation through the depth electrodes was performed during memorization (Figure 1). The pre and postoperative memory function were evaluated using Mini-Mental State Examination (MMSE) and Wechsler Memory Scale-Revised (WMS-R) and were compared in 6 patients who underwent AHP. Results: Table 1 shows the results of the provocative test and postoperative memory functional outcome. Out of the 10 patients, delayed recall and recognition tasks following electrical stimulation during memorization were performed in 8 and 10 patients respectively for verbal memory. Visual memory task was performed in 7 patients. Following electrical stimulation during memorization, delayed recall for verbal memory was affected in 6 out of 8 and recognition in 6 out of 10 patients. Among the 6 patients who underwent AHP, postoperative memory impairment developed in 2 patients in whom disturbances of both delayed recall and recognition for verbal memory were provoked. In contrast, memory function was intact in 3 without provoked verbal memory disturbance and also in one who demonstrated only provoked disturbance of delayed recall for verbal memory. None of the patients demonstrated provoked visual memory disturbance. AHP was considered not applicable to the remaining 4 patients based on the result of the provocative test. Conclusions: Our result suggests that recognition tasks following electrical stimulation during memorization is the most predictive for the possibility of postoperative memory impairment. Provocative test using depth electrodes implanted in the entorhinal area might be promising in preventing the memory disturbance following AHP of dominant hemisphere. This technique warrants further evaluation as a predictive tool for possible post-AHP memory impairment.