Temporal Lobe Epilepsy Resection May Disrupt Hippocampal Memory Network

Kathrin Wagner, MD, neuropsychologist, Epilepsy Centre, Medical Center of the University of Freiburg

Kathrin Wagner, MD

Results from a new study suggest that patients with temporal lobe epilepsy (TLE) with a nonlesional and nonepileptogenic hippocampus can experience hippocampal atrophy and memory decline as a result of resection in the temporal lobe, caused by a disruption of the memory network.

The work, conducted by Kathrin Wagner, MD, neuropsychologist, Epilepsy Centre, Medical Center of the University of Freiburg, and colleagues, included 55 patients who were evaluated presurgery and at 5 months postsurgery. The data showed that hippocampal volume (HV) loss was identified in both the ipsilateral and contralateral sides of the surgery (P <.001), with postoperative left HV loss being a significant predictor of verbal memory deterioration in those undergoing left-side surgery (n = 31; P <.01).

When considered in combination with preoperative verbal memory performance, postoperative HV on the left was able to elucidate almost 60% of the variation (P <.0001), though right side HV was not a significant predictor of visual memory performance.

“A disruption of the memory network by any resection within the temporal lobe, especially within the language&#8208;dominant hemisphere, may lead to hippocampus atrophy and memory decline,” Wagner and colleagues wrote. “These findings may further improve the counseling of patients concerning their postoperative memory outcome before temporal lobe resections sparing the entire hippocampus.”

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The Verbal Learning and Memory Test (VLMT) was used to investigate changes in verbal memory, while visual learning and memory were assessed with a revised iteration of the Diagnosticum fuer Cerebralschaedigung (DCS-R).

Postoperative verbal memory performance was influenced positively by preoperative performance (P <.01), and negatively impacted by left-sided surgery (P <.01). After left-sided surgery, those with a smaller postoperative left HV performed lower in verbal memory than those with larger left HV, regardless of their verbal memory performance prior to surgery.

After right-sided surgery, Wagner et al. observed increased performance in verbal memory performance compared to left-sided surgery (repeated-measures analysis of variance [rmANOVA]: F = 5.91; P <.05), though this did not reach significance for the interaction between time point and side of surgery (F = 2.59; P = .11).

Visual memory performance, meanwhile, trended toward loss over time (F = 3.51; P = .07), though neither side of surgery impact nor interactions of significance were identified. A better baseline performance significantly predicted higher post-surgical performance (P <.0001), with right HV and side of surgery showing a significant interaction (P <.05). Right-side HV was positively linked to better postoperative visual memory performance, though the association was slight.

Larger resection volumes were associated with smaller postoperative HV, irrespective of the side of surgery (left: P <.05; right: P <.01).

“To our knowledge, no study to date has investigated secondary hippocampal atrophy and its association with memory performance in patients with temporal lobe resections that spared the entire hippocampus,” Wagner and colleagues wrote. “Postoperative hippocampal shrinkage associated with memory decline has been described previously in patients receiving partial hippocampus resections. HV and memory loss were also observed in our patient group, even though the hippocampus was completely spared to preserve functional tissue.”

They added that due to the integral role the hippocampus plays in the distributed memory network made up of different structures within and beyond the temporal lobe, assuming that any resection of the temporal lobe which causes disruption to this network may lead to secondary hippocampal atrophy and corresponding memory disturbances.

As far as seizures were concerned, 69.1% (n = 38) of patients were completely seizure-free at follow-up, with 42 patients classified as Engel class 1, 8 as Engel class 2, 2 as Engel class 3, and 3 as Engel class 4. Those who still had ongoing seizures (n = 17; ipsilateral −0.42 ±0.35 mm³; contralateral −0.06 ±0.11 mm³) did not have significantly different postoperative HV loss compared to those who were seizure-free (ipsilateral, −0.67 ±0.47 mm³; contralateral, −0.07 ±0.12 mm³; P >.01).

REFERENCE

Wagner K, Gau K, Metternich B, et al. Effects of hippocampus-sparing resections in the temporal lobe: Hippocampal atrophy is associated with a decline in memory performance. Epilepsia. Published online March 12, 2020. Accessed March 18, 2020. doi: 10.1111/epi.16473