Abstracts

Rationale: To provide follow up on seizure outcome and memory function after multiple hippocampal transections (MHT) of the hippocampus in patients with intractable mesial temporal lobe epilepsy (MTLE) and normal memory scores. Hippocampal anatomy suggests that the circuits of memory processing (transverse lamellae) may be different from those of seizure propagation (longitudinal pathways). Thus, transverse cuts may interrupt seizure circuitry without interfering with memory function. Methods: 13 patients with nonlesional MTLE had depth electrode recordings confirming hippocampal seizure onset and underwent MHT. Duration of epilepsy ranged between 5 and 55 years. Antiepileptic drugs (AEDs) were not changed postoperatively. Intraoperative monitoring was done with 5-6 hippocampal electrodes spaced at around 1 cm intervals, and spike counting for approximately 10 minutes before each cut. The number of transections ranged between 4 and 7. Neuropsychological assessment was completed preoperatively and at 6 months postoperatively for 5 patients and at 1 year postoperatively for 5 other patients. Results: There were no complications. MHT resulted in marked spike reduction (p=0.003, paired t-test) intraoperatively. 10 patients (77%) are seizure-free (average follow-up = 25 months, range 9-55 months) without medication changes. One of the 3 patients with persistent seizures had an MRI revealing incomplete transections, another proved to have a neocortical seizure focus, and the third had only 2 seizures in 4 years, one of which occurred during AED withdrawal. Using a 90% confidence interval for reliable change indices that were corrected for practice (RCI-P), Two of 9 dominant-side MHT patients (22.2%) 2 of 10 patients (20%) declined on auditory-verbal memory and 3 of 10 (30%) declined on visual-spatial memory after MHT, compared to 38% and 28% of patients who declined in auditory-verbal and visual-spatial memory (respectively) after L temporal lobectomy (Lineweaver et al. Epilepsia 2006;47:1895-1903). One of 10 patients (10%) improved reliably on visual-spatial memory after MHT, compared to 16% improved after L temporal lobectomy (Baxendale et al. Neurology 2008;71:1319-25). declined reliably on Auditory-Verbal Memory after MHT, and 3 of 9 patients (33%) declined reliably on Visual-Spatial Memory, while one patient (10%) improved on Visual-Spatial Memory after MHT. Right and left hippocampal volumes were not different preoperatively (n=12, p=0.64, Wilcoxon signed-rank test), but the transected hippocampal volume decreased postoperatively (p=0.0173). Conclusions: MHT provides an effective intervention and a safer alternative than to temporal lobectomy regarding memory preservation in patients with MTLE. MHTand appears to spare verbal memory in about 1 of 2 more L TLE patients compared to lobectomy, while yielding similar results to left temporal lobectomy for visual memory.