Abstracts

Rationale: Resecting the dominant hippocampus in epilepsy surgery has been shown to be associated with significant verbal memory deficits, especially in patients with intact verbal memory pre-surgically. Multiple hippocampal transections (MHT) is a relatively new method, designed to interrupt the longitudinal hippocampal circuitry involved in seizure propagation, and at the same time preserving the circular fibers involved in memory function. This technique has been used to treat mesial temporal lobe epilepsy in both dominant and non-dominant cases. It is applied to either normal or sclerotic hippocampi. Although there is literature on using MHT in cases where there are “nearby” lesions to the hippocampus, no detailed description of the location and relationship of these lesions to the hippocampus exists. Here we report the first detailed case of MHT in a left (dominant), functional hippocampus with an amygdalar tumor abutting and displacing it. Methods: A 12-year-old, right-handed boy presented with refractory left temporal lobe epilepsy since the age of 4 months. Semiology was behavioral arrest and loss of memory (dialeptic seizure) followed by occasional secondary generalization. Average frequency was 2/month. Ictal onset was in the left temporal region on surface electroencephalography (EEG). Magnetic resonance imaging (MRI) showed an amygdalar tumor pushing a normal looking hippocampus posteriorly. Functional MRI showed left hemispheric language and speech dominance. Neuropsychology evaluation showed average verbal and visual memory scores without deficits. A WADA test revealed left language dominance and bilateral memory representation. Case was presented to the multidisciplinary epilepsy surgery conference (MESC) and consensus was to proceed with an invasive stereo EEG (SEEG) study to confirm the ictal onset zone. Results: Orthogonal depth electrodes were placed stereotactically sampling the left temporal tip, amygdala, hippocampal head and body, basal temporal region, posterior temporal region, anterior and posterior insulae and the orbitofrontal region. Interictals arose from the contacts in the hippocampal head and body, temporal tip and basal temporal regions and to a lesser extent the amygdalar tumor. Typical seizures arose from the hippocampal head and spread posteriorly to the hippocampal body and the rest of the temporal lobe. Case represented at MESC and MHT recommended to preserve the memory function in the left hippocampus. MHT were performed through a transsylvian approach and using intraoperative monitoring to gauge the effectiveness in suppressing the hippocampal discharges. Initial transections of the middle hippocampal body and tail did not abolish the spikes, nor did resecting the amygdalar tumor. Finally transecting the hippocampal head produced >90% improvement in the amplitude and frequency of interictals. Patient became seizure free after surgery till 9 months postoperatively when he had one breakthrough seizure. He has had no further seizure since then at the last follow up visit, 14 months post-operatively. Repeat neuropsychology evaluation at 7 months postoperatively showed no deficits in verbal or visual memory scores. Conclusions: There is no detailed literature of utilizing MHT in cases of tumors adjacent to the hippocampus in a pediatric patient. This is the first case in the literature to provide clear clinical, electrophysiologic, imaging and neuropsychological details of MHT successfully treating epilepsy in a structurally normal appearing hippocampus with an abutting amygdalar tumor. This case expands the application of MHT beyond the traditional sclerotic or normal hippocampi. Additionally, this is the youngest patient to receive MHT reported to date. Funding: None.