Combining fMRI Language Lateralization and Hippocampal Morphometry for Predicting Verbal Memory Outcome after Left Temporal Lobectomy (S28.003)

OBJECTIVE: To determine whether hippocampal volume measurements provide additional value beyond fMRI language lateralization alone in predicting verbal memory outcome in epilepsy following left anterior temporal lobectomy (L-ATL). BACKGROUND: Verbal memory decline is frequent after L-ATL and can be predicted with fair accuracy using an fMRI index of language lateralization. Here, we investigated the predictive value of hippocampal morphometry alone and in conjunction with fMRI. DESIGN/METHODS: Participants were 66 left temporal lobe epilepsy patients treated with L-ATL. All patients underwent preoperative fMRI using a semantic decision – tone decision contrast to measure language lateralization. All patients had preoperative and 6-month postoperative verbal memory testing, including a word-list learning and retention measure (Selective Reminding Test) and a story recall test (Wechsler Logical Memory). T1-weighted preoperative MRI scans were analyzed with FreeSurfer software to create automated initial parcellations of the hippocampus, which were then manually edited based on standard landmarks. RESULTS: Unlike fMRI language lateralization, the hippocampal volume measures provided no additional value for predicting postoperative change on the word-list learning test. In contrast, hippocampal volume was superior to fMRI for predicting change on the story memory test, with larger left hippocampal volume (r = -.361, p = .003) and smaller rightward hippocampal asymmetry (r = -.259, p = .037) correlating with greater decline in performance. Left hippocampal volume remained an independent predictor of story memory change after including fMRI and preoperative performance in a multivariate regression model (R2 change = .075, p = .027). CONCLUSIONS: Preoperative left hippocampal volume was predictive of postoperative change on a story recall task, whereas rote word-list learning was linked more closely to language lateralization. Encoding of meaningful stories likely engages bihemispheric semantic networks that are partially independent of the language system. Hippocampal morphometry adds predictive value for risk assessment prior to L-ATL surgery. Supported by: National Institute of Neurological Diseases and Stroke grant R01 NS35929. Disclosure: Dr. Bauer has nothing to disclose. Dr. Swanson has nothing to disclose. Dr. Sabsevitz has nothing to disclose. Dr. Stengel has nothing to disclose. Dr. Humphries has nothing to disclose. Dr. Rozman has nothing to disclose. Dr. Janecek has nothing to disclose. Dr. Raghavan has nothing to disclose. Dr. Mueller has nothing to disclose. Dr. Binder has received research support from the National Institutes of Health.