Multiple Hippocampal Transections Research Articles

Ultrasound-Navigated Multiple Hippocampal Transections: An Anatomical Study.

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

Left Temporal Pole Encephalocele With Independent Hippocampal Seizures: Surgical Strategy and Relevance of Epileptic Biomarkers.

Temporal pole encephalocele (TE) is an increasingly recognized surgically treatable subtype of refractory temporal lobe epilepsy that rarely shows hippocampal involvement. A 27-year-old patient presented with medically intractable epilepsy because of a left temporal pole encephalocele with a normal hippocampus on MRI. Extraoperative electrocorticography showed independent seizure onset with distinct morphology of seizure onset pattern from the temporal pole encephalocele and hippocampus. Additional analysis of ictal and interictal fast ripples revealed different electrophysiological fast ripple profiles in the two seizure onset zones. The patient underwent temporopolar disconnection, eliminating the need for large dural repair and multiple hippocampal transections that helped preserve the intrahippocampal and extrahippocampal memory pathways. Herein, the authors report that independent hippocampal seizures can be observed in patients with temporal pole encephalocele. Features of the ictal and interictal fast ripples can differ depending on the morphology of the seizure onset pattern. The authors suggest that, the interpretation of fast ripples in clinical practice should take seizure onset patterns into consideration.

Epilepsy surgery for dominant-side mesial temporal lobe epilepsy without hippocampal sclerosis

Although anterior temporal lobectomy (ATL) is an established surgery for medically intractable mesial temporal lobe epilepsy (MTLE), it can harm memory function, especially in dominant-side MTLE patients without hippocampal sclerosis (HS). To avoid this complication, multiple hippocampal transection (MHT) was developed, but its efficacy has not been fully elucidated. We report the detailed treatment results of MHT compared with that of ATL. We retrospectively analysed the records of 30 patients who underwent surgery for dominant-side MTLE. ATL was completed for 23 patients with HS, and MHT was completed for 7 patients without HS. The seizure control status, number of anti-seizure medicines, neurocognitive function, and psychiatric disorders of each patient were reviewed. The mean follow-up period was 70 months. Seizure control of Engel class I was achieved in 16 patients (70%) in the ALT group versus 5 patients (71%) in the MHT group. The mean number of anti-seizure medicines administered in the ATL group changed significantly from 2.4 to 1.9 (p = 0.01), while that in the MHT group was unchanged (from 2.1 to 2.0, p = 0.77). Eleven patients (48%) in the ATL group developed psychiatric disorders during the postoperative follow-up period, whereas no psychological complications were observed in the MHT group. Neither group showed neurocognitive decline after the surgery in any of the WAIS-III or WMS-R subtests. In conclusion, MHT may achieve reasonable postoperative seizure reduction, preserve neurocognitive function, and reduce postoperative psychiatric complications. Therefore, it can be considered as a therapeutic option for dominant-side MTLE without HS.

Neurophysiological Aspects of Multiple Hippocampal Transection in Temporal Epilepsy

Neurophysiological Aspects of Multiple Hippocampal Transection in Temporal Epilepsy

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.

For the treatment of mesial temporal lobe epilepsy on the language-dominant side in patients at high risk of memory decline, we propose 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. We report the efficacy and safety of this procedure in a preliminary observational study of cases. Five patients at high risk of memory decline, including three with non-lesional hippocampi on MRI, had temporal lobe epilepsy (TLE) necessitating depth electrode implantation. A new strategy of SEEG electrode placement was used to mimic MHT. After confirming hippocampal seizure onset, all the patients had three linear ablations perpendicular to the amigdalohippocampal complex. The procedure was performed at the patient's bedside with the patient awake during the full length of the procedure. Four out of five patients were seizure-free (average follow up: 14-18 months). There were no associated complications. Visual inspection of brain MRI of patients at six months following SEEG-guided RF-MHT showed significant hippocampal volume preservation. Subjects who received the procedure in the dominant side reported no subjective memory complaints in the follow-up clinic assessments at six months. Our preliminary seizure outcome seems very promising since the majority of our patients (four out of five patients) were 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.

Multiple hippocampal transections for mesial temporal lobe epilepsy.

Background: The purpose of this study was to evaluate the effectiveness of multiple hippocampal transections (MHT) in the treatment of drug-resistant mesial temporal lobe epilepsy.Methods: Six patients underwent MHT at Burdenko Neurosurgery Center in 2018. The age of the patients varied from 18 to 43 years. All patients suffered from refractory epilepsy caused by focal lesions of the mesial temporal complex or temporal pole in dominant side. Postoperative pathology revealed neuronal-glial tumors in two patients, focal cortical dysplasia (FCD) of the temporal pole – in two patients, cavernous angioma – in one patient, and encephalocele of the preuncal area – in one patient.Results: All patients underwent surgery satisfactorily. There were no postoperative complications except for homonymous superior quadrantanopia. This kind of visual field loss was noted in four cases out of six. During the follow-up period five patients out of six had Engel Class I outcome (83.3%). In one case, seizures developed after 1 month in a patient with FCD in the uncus (Engel IVA). After surgery, three out of six patients developed significant nominative aphasia. Two patients relative to the preoperative level demonstrated improvement in delayed verbal memory after MHT. Two patients showed a decrease level in delayed verbal memory. In preoperative period, visual memory was below the normal in one patient. Delayed visual memory in two cases impaired compared to the preoperative level.Conclusion: MHT can be considered as an effective method of drug-resistant mesial temporal lobe epilepsy caused by tumors of the medial temporal complex. At the same time, MHT makes it possible to preserve memory in patients with structurally preserved hippocampus. However, MHT do not guarantee the preservation of memory after surgery.

Multiple hippocampal transections for refractory pediatric mesial temporal lobe epilepsy: seizure and neuropsychological outcomes.

Temporal lobe epilepsy (TLE) is the most common focal epilepsy across adult and pediatric age groups. It is also the most amenable to surgery, with excellent long-term seizure outcome. Most TLE cases have an epileptogenic zone in the mesial temporal structures, namely the hippocampus. Resecting the dominant hippocampus has been shown to be associated with significant verbal memory deficits, especially in patients with intact verbal memory scores presurgically. Multiple hippocampal transection (MHT) is a relatively new surgical technique designed to interrupt the longitudinal hippocampal circuitry involved in seizure propagation yet preserve the circular fibers involved in memory function. This technique has been used to treat mesial TLE in both dominant- and nondominant-hemisphere cases, almost exclusively in adults. It has been applied to normal and sclerotic hippocampi. In this study, information on 3 pediatric patients who underwent MHT for mesial TLE at Children's Wisconsin between 2017 and 2018 is included. Clinical, electroencephalographic, and neuropsychological features and outcomes are described in detail. MRI revealed a tumor in the amygdala with a normal hippocampus in 1 patient and hippocampal sclerosis in 2 patients. All patients underwent stereoelectroencephalography confirming the involvement of the hippocampus in seizure onset. MHTs were completed under intraoperative monitoring, with amygdala and temporal tip resection in all patients due to early spread to these regions. All patients had excellent seizure outcomes at 1 year, and 2 of the 3 patients remain seizure free at last follow-up (range 20-36 months), all with stable or improved neuropsychological profiles, including verbal memory. MHT is a relatively new surgical procedure designed to preserve essential memory circuitry while disrupting seizure propagation pathways in the hippocampus. A growing body of literature shows good seizure and neuropsychological results, but mainly in adults. This is the first series of MHTs used exclusively in children at one medical center, showcasing excellent seizure control and preservation of neuropsychological functioning. One of the patients is also the first described to have MHT in the setting of an amygdalar tumor abutting the hippocampus, further expanding the pathological setting in which MHT can be used effectively.

The epileptogenic zone in pharmaco-resistant temporal lobe epilepsy with amygdala enlargement.

Temporal lobe epilepsy with amygdala enlargement (TLE-AE) has been considered a subtype of TLE. We evaluated the epileptogenic zone in patients with TLE-AE, who underwent intracranial video-EEG (ivEEG) and/or intraoperative electrocorticography (ioECoG) as well as epilepsy surgery. Eleven patients with TLE-AE were enrolled and investigated based on seizure profile, volumetric MRI, the Wechsler Memory Scale-Revised (WMS-R), the location of seizure onset zone (SOZ) and irritative zone (IZ) based on ivEEG (n=8), the location of interictal epileptiform discharges (IEDs) based on ioECoG (11), surgical procedure, and seizure outcome. The mean age at seizure onset was 34.9 years (range: 23-57). The mean duration of seizures was 5.0 years (range: 1-10). The number of AEDs was 2.3 (range: 1-5). The mean seizure frequency was nine per month (range: 1-30/month). All patients presented with focal impaired awareness seizures with (n=9) and without (2) secondary generalized convulsions. Volumetric MRI analysis showed unilateral enlarged amygdala with statistical significance (p<0.01). None of the patients' hippocampi had any abnormality based on MRI. Pre-operative mean verbal, visual, and delayed recall scores based on the WMS-R were over 100. The SOZ and IZ were identified in both the amygdala and hippocampus in seven patients and in only the amygdala in one patient based on ivEEG. IEDs were identified in the hippocampus in six patients and in both the amygdala and hippocampus in four patients based on ioECoG. All 11 patients underwent anterior temporal lobectomy, including amygdala resection, with multiple hippocampal transections (dominant hemisphere: seven patients) and resection (non-dominant hemisphere: three patients). Nine (81.8%) of 11 patients achieved seizure freedom with a mean follow-up of 26 months (range: 12-47). Post-operative WMS-R results did not show any significant deterioration, with a mean follow-up of 15 months (range: 12-24). The resected amygdala showed no histopathological abnormality. The epileptogenic zone of TLE-AE involves both the amygdala and hippocampus. ivEEG may be needed to explore the SOZ in normal hippocampus in addition to enlarged amygdala. Amygdala resection and multiple hippocampal transections may control the epileptogenic limbic system and save memory function in patients with TLE-AE.

P19-T Neurophysiological evaluation in multiple hippocampal transections for intractable temporal epilepsy

The purpose of this study was to evaluate the neurophysiological tactic in 9 patients during the multiple hippocampal transections (MHT). 9 patients with temporal lobe epilepsy underwent MHT, lesionectomy in uncus and nearby hippocampus, with additional resections in pole in 4 patients. Follow up was more than 6 months. The left dominant hemisphere was affected in all cases. They had normal or nearly normal memory function. Intraoperatively ECoG was performed on basal and lateral temporal cortex and leaded resection of possible lesion. ECoG was then recorded from strip of 4-6 electrodes over hippocampus and amygdala region. Transections were performed and then added to posterior part when epileptiform discharges persisted. After multiple transections were made control ECoG was repeated. 7 patients are seizure free, one has IIIA outcome and one has IVA. Memory worsening occured in 1 patient with intraoperative vascular damage in hippocampus. The epileptiform activity completely disappeared in hippocampus in 7 cases. Local epileptiform patterns were observed limited under 1 electrode in hippocampus in 2 patients. Basal epileptiform discharges persisted after MHT in 6 patients. It was significantly reduced in 4 cases, in 2 with local predominance. Residual cortical epileptiform activity was presented in the form of high-amplitude spikes. Spread of discharges from the basal or lateral cortex to hippocampus was suspected when small spikes persisted and were observed over a wide area of the hippocampus simultaneously with high amplitude cortical spikes, noted in 2 cases. Precise neurophysiologic evaluation is crucial for epilepsy surgery using MHT.

T03. Responsive Neurostimulation Device (RNS) vs. Multiple Hippocampal Transections (MHT) as treatments for refractory Temporal Lobe Epilepsy (TLE) – Outcomes from a single center, the University of California, Davis Medical Center (UCDMC)

Temporal lobectomy remains the gold standard for treatment of refractory TLE. However, patients with preserved or significantly asymmetric memory are not considered resection candidates due to the potential of memory deficits postoperatively. In our center these patients are offered placement of RNS or to undergo MHT. Some patients also undergo additional resection wherever possible. There are no head to head studies comparing these two procedures, we retrospectively compared clinical outcomes in patients with refractory TLE who have undergone RNS or MHT. 6 consecutive patients with the seizure onset zone in the dominant temporal lobe underwent either placement of RNS or had MHT at UCDMC. Of these patients, 2 had RNS placement, 2 had MHT only, and 2 had MHT plus resection of other temporal lobe structures. For these 6 patients, we analyzed post procedure clinical outcomes and presence of adverse effects. Median duration following intervention was 29 months in the RNS group and 5 in the MHT group. One of the RNS patients is seizure free 30 months after the implant, while the other showed no changes in seizure frequency or severity 28 months post implant. In that patient, the device was not capturing the seizures as determined by invasive monitoring which both RNS patients had prior to implantation. We were able to change the detection parameters; however not enough clinical data is currently available to determine if this lead to seizure reduction. Alternatively, 3 of 4 MHT patients had significant seizure reduction and 2 are seizure free at 4 and 6 months postoperatively. 2 patients had additional resection (amygdala ± temporal neocortex). 2 of the 4 MHT patients had invasive monitoring prior to the procedure; out of these, 1 is seizure free and 1 did not respond to the procedure. 2 of the 4 MHT patients self-reported word finding difficulties at the last follow up and 3 reported changes in mood and/or behavior. These were worse in the patients who had additional resection. Taking into consideration the limited size of our cohort and short study duration, our results suggest that in patients with refractory dominant TLE who are poor candidates for standard resection, MHT is more likely to lead to significant reduction in seizures; however was also associated with word finding difficulties and changes in mood and behavior. On the other hand, RNS did not result in any deficits and implanting the device offers more flexibility in terms of where the epileptic network maybe stimulated with a goal of optimizing clinical outcomes. Further observations of seizure frequency and standard assessments of higher integrative functions are needed to determine the long term impact of these procedures in order to better delineate who will benefit from one procedure over the other.

Resection of Temporal Neocortex During Multiple Hippocampal Transections for Mesial Temporal Lobe Epilepsy Does not Affect Seizure or Memory Outcome.

Multiple hippocampal transection (MHT) is a surgical treatment for mesial temporal lobe epilepsy associated with improved postoperative neuropsychological outcomes compared with lobectomy. To determine whether resection of the amygdala and anterior temporal neocortex during MHT affects postoperative seizure/memory outcome. Seventeen patients with normal magnetic resonance imaging and stereo-electroencephalogram-proven drug-resistant dominant mesial temporal lobe epilepsy were treated with MHT. Nine patients underwent MHT alone (MHT-) and 8 patients underwent MHT plus removal of the amygdala and anterior 4.5 cm of temporal neocortex lateral to the fusiform gyrus (MHT+). Verbal and visual-spatial memory were assessed in all patients preoperatively and in 14 patients postoperatively using the Wechsler Memory Scale. Postoperative seizure control was assessed at 12 months for all patients. Overall, 11 of 17 patients (64.7%) were Engel class 1 at 1 year (6/9 MHT-, 5/8 MHT+, P = .38), and 10 of 14 patients (71.4%) had no significant postoperative decline in either verbal or visual memory (6/8 MHT-, 4/6 MHT+, P = .42). Verbal memory declined in 2 of 8 MHT- and 1 of 6 MHT+ patients, and visual memory declined in 1 of 8 MHT- and 2 of 6 MHT+ patients. Two patients had improved visual memory postoperatively, both in the MHT+ group. MHT on the dominant side is associated with high rates of seizure freedom and favorable memory preservation outcomes regardless of the extent of neocortical resection. Preservation of the temporal neocortex and amygdala during MHT does not appear to decrease the risk of postoperative memory decline, nor does it alter seizure outcome.

Long-term outcome and neuroradiologic changes after multiple hippocampal transection combined with multiple subpial transection or lesionectomy for temporal lobe epilepsy.

Multiple hippocampal transection (MHT) is a surgical procedure developed to avoid postoperative memory decline. Its efficacy has been documented in only a few small series with relatively short observation periods. We prospectively evaluated the long-term seizure and cognitive outcomes of MHT combined with multiple subpial transection or lesionectomy (MHT + MST/L). Moreover, we quantitatively evaluated the structural and metabolic neuroradiologic changes after the procedure to elucidate the anatomofunctional correlates of memory preservation. Twenty-four patients underwent MHT + MST/L for treatment of drug-resistant mesial temporal lobe epilepsy (mTLE) and were followed for more than 5 years. Indications for the procedure were the following: (1) verbally dominant-sided surgery in patients with a radiologically normal hippocampus or normal/near normal memory, and (2) surgery for patients with concomitant epileptic activity on the contralateral side, that is, when the surgery was considered a high risk for severe postoperative memory decline. Seizure outcome was evaluated using Engel's classification 1, 2, and 3 years after surgery, and at the last visit (LV). Three subgroups were evaluated as well: magnetic resonance imaging (MRI) negative (MN), hippocampal sclerosis (HS), and normal hippocampus with extrahippocampal lesion (NHEL). The long-term cognitive outcome was followed through to LV in patients who underwent verbally dominant-sided surgery. Hippocampal volume (HV), diffusion tensor parameters (DTP), and glucose utilization (GU) were determined from MRI and fluorodeoxyglucose-positron emission tomography (FDG-PET) studies performed before and >6 months after surgery. Whereas the rate of Engel class I as a whole was 71% at 1 year and 67% at LV, the rates in the MN, HS, and NHEL groups were 60%, 67%, and 100% at 1 year, respectively, and 70%, 56%, and 80% at LV, respectively. Memory indices after verbally dominant-sided surgery transiently declined at 1 month but recovered to and remained at the preoperative level through LV. The HV, DTP of the fornix, and GU of the temporal lobe on the treated side showed pathologic changes even when the transiently declined memory indices had recovered to the preoperative level. The long-term outcome for complex partial seizures after MHT + MST/L was comparable to that seen after anterior temporal lobectomy. The long-term cognitive outcome was favorable, even for patients with a high risk of severe postoperative memory decline. MHT + MST/L may be a treatment option for mTLE in which resective surgery carries a risk of postoperative memory decline, particularly in patients without MRI lesion. A discrepancy between the preserved memory and the pathologic neuroradiologic changes indicates the necessity for further studies including functional MRI.

Multiple hippocampal transections for intractable hippocampal epilepsy: Seizure outcome.

The purpose of this study was to evaluate the seizure outcomes after transverse multiple hippocampal transections (MHTs) in 13 patients with intractable TLE. Thirteen patients with normal memory scores, including 8 with nonlesional hippocampi on MRI, had temporal lobe epilepsy (TLE) necessitating depth electrode implantation. After confirming hippocampal seizure onset, they underwent MHT. Intraoperative monitoring was done with 5-6 hippocampal electrodes spaced at approximately 1-cm intervals and spike counting for 5-8min before each cut. The number of transections ranged between 4 and 7. Neuropsychological assessment was completed preoperatively and postoperatively for all patients and will be reported separately. Duration of epilepsy ranged between 5 and 55years. There were no complications. Intraoperatively, MHT resulted in marked spike reduction (p=0.003, paired t-test). Ten patients (77%) are seizure-free (average follow-up was 33months, range 20-65months) without medication changes. One of the 3 patients with persistent seizures had an MRI revealing incomplete transections, another had an additional neocortical seizure focus (as suggested by pure aphasic seizures), and the third had only 2 seizures in 4years, one of which occurred during antiseizure medication withdrawal. Verbal and visual memory outcomes will be reported separately. Right and left hippocampal volumes were not different preoperatively (n=12, p=0.64, Wilcoxon signed-rank test), but the transected hippocampal volume decreased postoperatively (p=0.0173). Multiple hippocampal transections provide an effective intervention and a safe alternative to temporal lobectomy in patients with hippocampal epilepsy.

Status epilepticus results in region-specific alterations in seizure susceptibility along the hippocampal longitudinal axis

Temporal lobe epilepsy (TLE) is the most common epilepsy syndrome in adults. In particular, the hippocampus is highly susceptible to abnormal synchronization. Recent advances in the surgical treatment of patients with refractory TLE have shown that multiple hippocampal transections can effectively control seizures. It has been suggested that in TLE the synchrony in the longitudinal connections is required for seizure generation; however the physiological background for the increase in hippocampal synchronization along the longitudinal axis is not fully understood. The hippocampus varies in seizure susceptibility along its longitudinal axis with the ventral hippocampus (VH) region being more seizure-prone and susceptible to neuronal damage than the dorsal hippocampus (DH). In the present study we studied seizure susceptibility along the longitudinal axis of the hippocampus following pilocarpine-induced status epilepticus (SE). In control conditions the VH generates epileptiform activity (EA) more frequently than the DH when exposed to a low Mg(2+)/1Ca(2+)/5K(+) solution. Following SE the probability of inducing epileptiform activity (EA) is similar in the VH and DH slices. This SE-induced change is due to an increase in the proportion of DH slices responding to the low Mg(2+)/1Ca(2+)/5K(+) solution with EA. Moreover, both the VH and DH show similar responses to a low Mg(2+)/1Ca(2+)/5K(+) solution. These findings indicate that the hippocampus undergoes significant functional changes following SE, which may provide the necessary increase of synchrony along the longitudinal axis to generate seizures in TLE.

Long term follow-up after multiple hippocampal transection (MHT)

PurposeMultiple hippocampal transection (MHT) is a new surgical procedure which disrupts seizure propagation within the hippocampus without impairing verbal memory or the loss of stem cells. Since there are very few papers on this procedure, the authors are presenting their long term results to increase the database on this procedure. MethodLong term outcome in 15 consecutive patients who had MHT for unlilateral temporal lobe epilepsy, had intra-operative electro-corticography (ECoG) and have a minimum follow-up of at least 2 years is presented. The male/female ratio is 2/1; follow-up is 24–60 months (median of 41 months); and ages between 25 and 60 years. All patients had multiple subpial transection (MST) on the neocortex and MHT on the hippocampus. Amygdalectomy was done if seizure focus was present in the amygdala (10 patients). Temporal tip (1.5–2.5cm in length) was resected (11 patients) when it was resistant to MST, based on intraoperative EEG recordings. ResultsThere was no permanent neurological complication. Fourteen patients (94.7%) are seizure free (Engel's Class I) and 1 (5.3%) has rare seizures (Class II). Neuropsychological studies showed that verbal memory was preserved. ConclusionThe results show that the seizure outcome with MHT is equal or better than those reported with standard temporal lobectomy. Furthermore verbal memory is preserved. The study also shows that intraoperative ECoG is important in order to conclude adequacy of the procedure. Based on the result of this study the authors feel that this procedure needs to be persued as an alternate to hippocampectomy.

173 Long-term Follow-up After Multiple Hippocampal Transection (MHT)

INTRODUCTION: The conventional procedure of hippocampectomy can impair memory. Furthermore, the hippocampus is the main source of stem cells. On the other hand, multiple hippocampal transection (MHT) can disrupt seizure circuits without loss of function or stem cells. In this presentation therefore, the authors will present long term outcomes in patients who had MHT for unilateral temporal lobe epilepsy. METHODS: There were 15 patients with a male/female ratio of 2-to-1; follow-up of 24 to 60 months (median of 41 months); and ages between 25 and 60 years. Preoperative electrocorticography (ECoG) was done using subdural and depth electrodes. All patients had multiple subpial transection (MST) on the neocortex and MHT on the hippocampus. Access to the hippocampus was gained through the middle temporal gyrus. Transverse cuts were made in the hippocampus at 4 mm intervals. The fimbria and entorhinal cortex were left intact. Amygdala was removed if it was epileptogenic (10 patients). Intraoperative ECoG was then done. If recordings showed epileptogenic activity, transections were repeated. If this activity persisted, the involved neocortex was resected. RESULTS: Based on intraoperative ECoG, repeat transections were needed in every case; though the second pass was over a much smaller area. Resection of temporal tip (1-2.5 cm diameter) was needed in 11 patients. There were no permanent neurological complications. Fourteen patients (94.7%) are Seizure free (Engel's class I) and 1 (6%) has rare seizures (class II). Neuropsychological studies showed that verbal memory was preserved. CONCLUSION: Although the series is small the long-term follow-up is adequate to draw preliminary conclusions. The results show that the seizure outcome with MHT is better than those reported with standard temporal lobectomy. The study also shows that intraoperative ECoG is important in order to conclude adequacy of the procedure. These conclusions indicate that this procedure needs to be persued as an alternate to hippocampectomy.

Seizure Outcome and Memory Function after Multiple Hippocampal Transections (IN5-1.009)

Objective: To evaluate seizure outcome and memory function after multiple hippocampal transections (MHT) of the hippocampus in intractable nonlesional mesial temporal lobe epilepsy (MTLE). Background Hippocampal anatomy suggests that the circuits of memory processing (transverse lamellae) are different from those of seizure propagation (longitudinal pathways). Thus, transverse cuts may interrupt seizure circuitry without interfering with memory function. Design/Methods: 13 patients with nonlesional MTLE had depth electrode recordings confirming hippocampal seizure onset and underwent MHT. Duration of epilepsy ranged between 5 and 55 years. Antiepileptic drugs (AEDs) were not changed postoperatively. Intraoperative monitoring was done with 5-6 hippocampal electrodes spaced at around 1 cm intervals, and spike counting for approximately 10 minutes before each cut. The number of transections ranged between 4 and 7 resulting in marked spike reduction (p=0.003, paired t-test). Neuropsychological assessment was done preoperatively and 1 year postoperatively in all patients. Results: There were no complications. 10 patients (77%) are seizure-free (follow-up>1 year in 8 patients, and 0.3). Conclusions: MHT provides an effective intervention and a safer alternative than temporal lobectomy regarding memory preservation in patients with nonlesional MTLE. Disclosure: Dr. Kahriman has nothing to disclose. Dr. Miller has nothing to disclose. Dr. Macinuas has nothing to disclose. Dr. Bailey has nothing to disclose. Dr. Fastenau has nothing to disclose. Dr. Syed has nothing to disclose. Dr. Amina has nothing to disclose. Dr. Tanner has received personal compensation for activities with GlaxoSmithKline, Inc. as a speaker. Dr. Karanec has nothing to disclose. Dr. Luders has nothing to disclose. Dr. Koubeissi has received personal compensation for activities with UCB Pharma and Pfizer Inc as a speaker.

Seizure Outcome and Memory Function after Multiple Hippocampal Transections (S46.006)

Seizure Outcome and Memory Function after Multiple Hippocampal Transections (S46.006)

Requirement of longitudinal synchrony of epileptiform discharges in the hippocampus for seizure generation: a pilot study

The goal in this study was to assess the role of longitudinal hippocampal circuits in the generation of interictal and ictal activity in temporal lobe epilepsy (TLE) and to evaluate the effects of multiple hippocampal transections (MHT). In 6 patients with TLE, the authors evaluated the synchrony of hippocampal interictal and ictal epileptiform discharges by using a cross-correlation analysis, and the effect of MHT on hippocampal interictal spikes was studied. Five of the 6 patients were studied with depth electrodes, and epilepsy surgery was performed in 4 patients (anterior temporal lobectomy in 1 and MHT in 3). Four hundred eighty-two (95.1%) of 507 hippocampal spikes showed an anterior-to-posterior propagation within the hippocampus, with a fixed peak-to-peak interval. During seizures, a significant increase of synchronization between different hippocampal regions and between the hippocampus and the ipsilateral anterior parahippocampal gyrus was observed in all seizures. An ictal increase in synchronization between the hippocampus and ipsilateral amygdala was seen in only 24.1% of the seizures. No changes in synchronization were noticed during seizures between the hippocampi and the amygdala on either side. The structure leading the epileptic seizures varied over time during a given seizure and also from one seizure to another. Spike analysis during MHT demonstrated that there were two spike populations that reacted differently to this procedure--namely, 1) spikes that showed maximum amplitude at the head of the hippocampus (type H); and 2) spikes that showed the highest amplitude at the hippocampal body (type B). A striking decrease in amplitude and frequency of type B spikes was noticed in all 3 patients after transections at the head or anterior portion of the hippocampal body. Type H spikes were seen in 2 cases and did not change in amplitude and frequency throughout MHT. Type B spikes showed constantly high cross-correlation values in different derivations and a relatively fixed peak-to-peak interval before MHT. This fixed interpeak delay disappeared after the first transection, although high cross-correlation values persisted unchanged. All patients who underwent MHT remained seizure free for more than 2 years. These data suggest that synchronized discharges involving the complete anterior-posterior axis of the hippocampal/parahippocampal (H/P) formation underlie the spread of epileptiform discharges outside the H/P structures and, therefore, for the generation of epileptic seizures originating in the H/P structures. This conclusion is supported by the following observations. 1) Hippocampal spikes are consistently synchronized in the whole hippocampal structures, with a fixed delay between the different hippocampal areas. 2) One or two transections between the head and body of the hippocampal formation are sufficient to abolish hippocampal spikes that are synchronized along the anterior-posterior axis of the hippocampus. 3) Treatment with MHT leads to seizure freedom in patients with H/P epilepsy.