Effects of hippocampus-sparing resections in the temporal lobe: Hippocampal atrophy is associated with a decline in memory performance.

Abstract

In patients with temporal lobe epilepsy (TLE) with a nonlesional and nonepileptogenic hippocampus (HC), in order to preserve functionally intact brain tissue, the HC is not resected. However, some patients experience postoperative memory decline, possibly due to disruption of the extrahippocampal memory network and secondary hippocampal volume (HV) loss. The purpose of this study was to determine the extent of hippocampal atrophy ipsilateral and contralateral to the side of the surgery and its relation to memory outcomes. Hippocampal volume and verbal as well as visual memory performance were retrospectively examined in 55 patients (mean age ± standard deviation [SD] 30±15years, 25 female, 31 left) before and 5months after surgery within the temporal lobe that spared the entire HC. HV was extracted based on prespecified templates, and resection volumes were also determined. HV loss was found both ipsilateral and contralateral to the side of surgery (P<.001). Postoperative left HV loss was a significant predictor of postoperative verbal memorydeterioration after left-sided surgery (P<.01). Together with the preoperative verbal memory performance, postoperative left HV explained almost 60% of the variance (P<.0001). However, right HV was not a clear predictor of visual memory performance. Larger resection volumes were associated with smaller postoperative HV, irrespective of side of surgery (left: P<.05, right: P<.01). A disruption of the memory network by any resection within the TL, especially within the language-dominant hemisphere, may lead to HC atrophy and memory decline. These findings may further improve the counseling of patients concerning their postoperative memory outcomebefore TL resections sparing the entire HC.