By: Dr. Alishba Batool
Hippocampal Transection: Multiple hippocampal transection (MHT) is a novel surgical procedure that serves to disrupt seizure propagation fibers within the hippocampus without impairing verbal memory or the loss of stem cells. However, there is little evidence available to guide neurosurgeons in selecting this technique for use in appropriate patients. It was developed in 2006 to minimize potential hippocampal damage, which can be significant in resection or ablation techniques.
Procedures: The MHT procedure involves multiple transections of the longitudinal fibers of the hippocampus that are parallel to the anterior-posterior length of the hippocampus and are putatively involved in seizure propagation The majority of patients with epilepsy may achieve symptomatic relief with antiepileptic medications, but up to 30% of patients develop medically refractory, intractable epilepsy. In these patients, localization and surgical removal of focal epileptogenic zones are important steps in achieving seizure remission. The most common form of focal intractable epilepsy in adults is mesial temporal lobe epilepsy (MTLE), for which definitive surgical treatment includes anterior temporal lobectomy (ATL) or selective amygdalohippocampectomy.
Benefits and Risks: These procedures are effective in preventing seizures. Patients may experience significant postoperative behavioral, memory, and language deficits, especially in patients whose underlying anatomy and neuropsychological functioning are normal at baseline.
What happens before, during, and after surgery?
Recently, stereotactic laser ablation has gained momentum as a more precise means of treatment, further highlighting the drive toward less destructive interventions. However, even this less intrusive alternative has been associated with neurological complications and variable outcomes concerning seizure freedom. MHT spares the circular fibers, which course perpendicular to the long axis of the hippocampus and are associated with the input and output neuronal circuitry pivotal in memory function. After the extent of the epileptic area is determined, multiple transections of the pyramidal layer under the alveus are performed using specially designed ring transectors. After this procedure, epileptic discharges from the hippocampus can be completely abolished.
How is it performed?
For the treatment of mesial temporal lobe epilepsy on the language-dominant side in patients at high risk of memory decline, a minimally invasive diagnostic and treatment technique, adopting the principles of multiple hippocampal transections (MHT) using stereo-electroencephalography-guided radiofrequency (SEEG-guided-RF-MHT). This new technique allows targeting of the longitudinal fibers in the hippocampus critical for seizure spreading while sparing the transverse circuits which are considered important for memory processing and avoiding discomfort and longer post-operatory recovery time associated with craniotomies.
A new strategy of SEEG electrode placement was used to mimic MHT. After confirming hippocampal seizure onset, patients have three linear ablations perpendicular to the amygdalohippocampal complex. The procedure is performed at the patient’s bedside with the patient awake during the full length of the procedure. Visual inspection of brain MRI of patients at six months following SEEG-guided RF-MHT showed significant hippocampal volume preservation. Patients who received the procedure on the dominant side reported no subjective memory complaints in the follow-up clinic assessments at six months, the majority of patients are seizure-free. Since no lesions are made outside the amygdalo-hippocampal complex using this technique and the temporal stem remains intact, more favorable memory and language outcome is expected in patients at high risk of memory decline.
To establish a correlation between intraoperative electrocorticography data and seizure monitoring after multiple hippocampal transections in patients with drug-resistant symptomatic medial temporal epilepsy. Hippocampal transection is performed until synchronized epileptiform activity in the hippocampus on the electrocorticogram ceases. Control of seizures is achieved after transection, and synchronized epileptiform activity in the hippocampus disappeared in all cases. Multiple hippocampal transections provided the opportunity to achieve cessation of synchronized spike activity in the hippocampus.
Resources:
Abramov, I., Jubran, J.H., Houlihan, L.M., Park, M.T., Howshar, J.T., Farhadi, D.S., Loymak, T., Cole, T.S., Pitskhelauri, D., and Preul, M.C. (2022). Multiple hippocampal transection for mesial temporal lobe epilepsy: A systematic review. Seizure: European Journal of Epilepsy,(101)162-176. Retrieved from: https://doi.org/10.1016/j.seizure.2022.08.007
Kozlova, A.B., Korsakova, M.B., Pitskhelauri, D.I. et al. Neurophysiological Aspects of Multiple Hippocampal Transection in Temporal Epilepsy. Neurosci Behav Physi 52, 842–848 (2022). https://doi.org/10.1007/s11055-022-01305-4
Losarcos, N.G., Miller, J., Fastenau, P., Amina, S., Bailey, C., Deveraux, M., Fernandez-Baca Vaca, G., Eyring, L.G., Lacuey, N., Park, J., Rose, M., Shahid, A., Thyagaraj, S., Zande, J., and Lüders, H. (2021). Stereotactic-EEG-guided radiofrequency multiple hippocampal transection (SEEG-guided-Rf-MHT) for the treatment of mesial temporal lobe epilepsy: a minimally invasive method for diagnosis and treatment. Epileptic Disorders,(23)5, 682-694. Retrieved from: https://doi.org/10.1684/epd.2021.1314
Patil, A. A., Chamczuk, A. J., & Andrews, R. V. (2016). Hippocampal Transections for Epilepsy. Neurosurgery clinics of North America, 27(1), 19–25. https://doi.org/10.1016/j.nec.2015.08.013
Pitskhelauri, D., Kudieva, E., Kamenetskaya, M., Kozlova, A., Vlasov, P., Dombaanai, B., Eliseeva, N., Shishkina, L., Sanikidze, A., Shults, E., Moshev, D., Pronin, I., & Melikyan, A. (2021). Multiple hippocampal transections for mesial temporal lobe epilepsy. Surgical neurology international, 12, 372. https://doi.org/10.25259/SNI_350_2021
