Abstracts

Rationale: Preoperative hippocampal volumes and hippocampal asymmetry indices may be useful as predictors of postoperative neuropsychological outcomes when planning surgical resection for medically refractory epilepsy. We investigated whether preoperative hippocampal volumes and asymmetry indices predict postoperative verbal memory declines. Methods: Thirty-four patients (mean age 36.7 +/- 10.4) referred to the Clinical Epilepsy Section, NINDS, NIH for evaluation of intractable epilepsy underwent a frontotemporal, temporoparietal, or temporal lobectomy. Preoperative hippocampal volumes were calculated for each patient from 1.5 or 3 T MPRAGE MRIs using FreeSurfer. Each patient completed pre- and postoperative neuropsychological testing with the Wechsler Memory Scale (WMS-III). We examined pre- to postoperative change in immediate and delayed verbal memory (Logical Memory subtest). Results: We found a significant relationship between preoperative right/left hippocampal ratio and postoperative decline in Logical Memory immediate score (F = 4.5, p = 0.04, r² = 0.14), independent of side of resection. We also examined percent of hippocampus resected and found that a larger resection predicted greater verbal memory decline irrespective of resection side (F = 7.5, p = 0.01, r² = 0.22). For patients with right-sided resections (n=17), relatively smaller preoperative right hippocampal volume was associated with increased postoperative verbal memory decline (Logical Memory Immediate: F = 6.9, p = 0.024; Logical Memory Delayed: F = 8.4, p = 0.02). No significant relationships were found between preoperative hippocampal volume and verbal memory outcomes for patients with left-sided resections. Conclusions: Greater preoperative hippocampal volume asymmetry (right>left) and larger hippocampal resections are both associated with postoperative verbal memory decline. Resection of a relatively smaller right hippocampus is associated with increased verbal memory decline, suggesting that right-sided resection may affect logical memory. Preoperative hippocampal volume asymmetry may be a useful predictor of postoperative verbal memory outcomes.