Multiple hippocampal transections for mesial temporal lobe epilepsy

Ultrasound-Navigated Multiple Hippocampal Transections: An Anatomical Study

BACKGROUND

 Multiple hippocampal transection (MHT) is a surgical technique used for the treatment of drug-resistant mesial temporal lobe epilepsy in situations where standard procedures would pose a high risk for memory deterioration. During MHT, the longitudinal fibers of the hippocampus, implicated in epilepsy spreading, are interrupted, while the transverse memory circuits are spared. The extent of MHT is governed by intraoperative electrocorticography; abolition of epileptic discharges serves as an end point to terminate the transection. In other words, the aim of MHT is not the anatomical completeness of hippocampal transection. In contrast, we hypothesize that only the complete transection of hippocampal cross-section is needed to durably terminate epilepsy, avoiding possible postoperative reorganization of longitudinal pathways. Here, we report an anatomical study designed to evaluate the feasibility of complete transection of hippocampus with the aid of ultrasound neuronavigation and we propose new instruments to reach this goal.

METHODS

 Five cadaveric brains were analyzed in this study. MHT was performed on both sides of each brain either with or without ultrasound neuronavigation. The percentage of transected cross-section of the hippocampus was measured using magnetic resonance imaging (MRI) and both sides were compared.

RESULTS

 The ultrasound-guided MHTs were more likely to achieve complete hippocampal transection compared with the nonnavigated MHT transection (73 vs 58%; p < 0.01). Our study also allowed us to propose specialized transectors to minimize invasivity of this procedure.

CONCLUSION

 Completeness of MHT can be better reached with the aid of an ultrasound neuronavigation system; modified instruments for this procedure were also designed.

The high frequency oscillations in the amygdala, hippocampus, and temporal cortex during mesial temporal lobe epilepsy

The mesial temporal lobe epilepsy (MTLE) seizures are believed to originate from medial temporal structures, including the amygdala, hippocampus, and temporal cortex. Thus, the seizures onset zones (SOZs) of MTLE locate in these regions. However, whether the neural features of SOZs are specific to different medial temporal structures are still unclear and need more investigation. To address this question, the present study tracked the features of two different high frequency oscillations (HFOs) in the SOZs of these regions during MTLE seizures from 10 drug-resistant MTLE patients, who received the stereo electroencephalography (SEEG) electrodes implantation surgery in the medial temporal structures. Remarkable difference of HFOs features, including the proportions of HFOs contacts, percentages of HFOs contacts with significant coupling and firing rates of HFOs, could be observed in the SOZs among three medial temporal structures during seizures. Specifically, we found that the amygdala might contribute to the generation of MTLE seizures, while the hippocampus plays a critical role for the propagation of MTLE seizures. In addition, the HFOs firing rates in SOZ regions were significantly larger than those in NonSOZ regions, suggesting the potential biomarkers of HFOs for MTLE seizure. Moreover, there existed higher percentages of SOZs contacts in the HFOs contacts than in all SEEG contacts, especially those with significant coupling to slow oscillations, implying that specific HFOs features would help identify the SOZ regions. Taken together, our results displayed the features of HFOs in different medial temporal structures during MTLE seizures, and could deepen our understanding concerning the neural mechanism of MTLE.

Multiple hippocampal transection for mesial temporal lobe epilepsy: A systematic review

PURPOSE

Multiple hippocampal transection (MHT) is a surgical technique that offers adequate seizure control with minimal perioperative morbidity. However, there is little evidence available to guide neurosurgeons in selecting this technique for use in appropriate patients. This systematic review analyzes patient-level data associated with MHT for intractable epilepsy, focusing on postoperative seizure control and memory outcomes.

METHODS

The systematic review was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Relevant articles were identified from 3 databases (PubMed, Medline, Embase) up to August 1, 2021. Inclusion criteria were that the majority of patients had received a diagnosis of intractable epilepsy, the article was written in English, MHT was the primary procedure, and patient-level metadata were included.

RESULTS

Fifty-nine unique patients who underwent MHT were identified across 11 studies. Ten (17%) of 59 patients underwent MHT alone. Forty-three (75%) of 57 patients who had a follow-up 12 months or longer were seizure free at last follow-up. With respect to postoperative verbal memory retention, 9 of 38 (24%) patient test scores did not change, 14 (37%) decreased, and 16 (42%) increased. With respect to postoperative nonverbal memory retention, 12 of 38 (34%) patient test scores did not change, 13 (34%) decreased, and 13 (33%) increased.

CONCLUSION

There are few reported patients analyzed after MHT. Although the neurocognitive benefits of MHT are unproven, this relatively novel technique has shown promise in the management of seizures in patients with intractable epilepsy. However, structured trials assessing MHT in isolation are warranted.