Comparison of mesial versus neocortical onset temporal lobe seizures: neurodiagnostic findings and surgical outcome

Temporal lobe epilepsy page: Role of temporal lobe structures and subjacent pathology in the intracranial ictal onset pattern in pediatric patients with temporal lobe epilepsy: A stereo-electroencephalogram analysis

OBJECTIVE

To determine the intracranial ictal onset and early spread patterns in pediatric patients with Temporal lobe epilepsy and its possible association with histopathology, temporal structure involved, mesial structural pathology, and possible implication in postsurgical outcome.

METHODS

A descriptive, retrospective, cross-sectional study was carried out in a group of children from Children's Wisconsin between 2016 and 2022.

RESULTS

This study showed a strong association between ictal onset patterns and underlying histology (p < 0.05). Low-Frequency High Amplitude periodic spikes were seen only in patients with HS (20.6 %). A strong statistically significant association was found between different ictal onset patterns and the temporal lobe structure involved in the ictal onset (p < 0.001). Seizures with ictal onset consisting of Slow Potential Shift with superimposed Low Voltage Fast Activity arise from the Inferior Temporal Lobe or Middle Temporal Gyrus in a more significant proportion of seizures than those that originated from mesial temporal structures (Difference of proportion; p < 0.05). Low Voltage Fast Activity periodic spikes as an ictal pattern were seen in a patient with seizures arising outside the mesial temporal structure. The most frequent early spread pattern observed was Low Voltage Fast Activity (89.4 %); this pattern did not depend on the type of mesial structure pathology. Ictal onset patterns were associated with postsurgical outcomes (p < 0.001). The ictal onset pattern depends on the histopathology in the ictal onset zone and the temporal lobe structure involved in the ictal onset (p = 0.001).

CONCLUSIONS

Intracranial ictal onset patterns in TEMPORAL LOBE EPILEPSY depend on underlying histology and the temporal lobe structure involved in its onset.

Identifying important factors for successful surgery in patients with lateral temporal lobe epilepsy

OBJECTIVE

Lateral temporal lobe epilepsy (LTLE) has been diagnosed in only a small number of patients; therefore, its surgical outcome is not as well-known as that of mesial temporal lobe epilepsy. We aimed to evaluate the long-term (5 years) and short-term (2 years) surgical outcomes and identify possible prognostic factors in patients with LTLE.

METHODS

This retrospective cohort study was conducted between January 1995 and December 2018 among patients who underwent resective surgery in a university-affiliated hospital. Patients were classified as LTLE if ictal onset zone was in lateral temporal area. Surgical outcomes were evaluated at 2 and 5 years. We subdivided based on outcomes and compared clinical and neuroimaging data including cortical thickness between two groups.

RESULTS

Sixty-four patients were included in the study. The mean follow-up duration after the surgery was 8.4 years. Five years after surgery, 45 of the 63 (71.4%) patients achieved seizure freedom. Clinically and statistically significant prognostic factors for postsurgical outcomes were the duration of epilepsy before surgery and focal cortical dysplasia on postoperative histopathology at the 5-year follow-up. Optimal cut-off point for epilepsy duration was eight years after the seizure onset (odds ratio 4.375, p-value = 0.0214). Furthermore, we propose a model for predicting seizure outcomes 5 years after surgery using the receiver operating characteristic curve and nomogram (area under the curve = 0.733; 95% confidence interval, 0.588-0.879). Cortical thinning was observed in ipsilateral cingulate gyrus and contralateral parietal lobe in poor surgical group compared to good surgical group (p-value < 0.01, uncorrected).

CONCLUSIONS

The identified predictors of unfavorable surgical outcomes may help in selecting optimal candidates and identifying the optimal timing for surgery among patients with LTLE. Additionally, cortical thinning was more extensive in the poor surgical group.

Drug-resistant epilepsy and mortality-Why and when do neuromodulation and epilepsy surgery reduce overall mortality

Patients with drug-resistant epilepsy have an increased mortality rate, with the majority of deaths being epilepsy related and 40% due to sudden unexpected death in epilepsy (SUDEP). The impact of epilepsy surgery on mortality has been investigated since the 1970s, with increased interest in this field during the past 15 years. We systematically reviewed studies investigating mortality rate in patients undergoing epilepsy surgery or neuromodulation therapies. The quality of available evidence proved heterogenous and often limited by significant methodological issues. Perioperative mortality following epilepsy surgery was found to be <1%. Meta-analysis of studies that directly compared patients who underwent surgery to those not operated following presurgical evaluation showed that the former have a two-fold lower risk of death and a three-fold lower risk of SUDEP compared to the latter (odds ratio [OR] 0.40, 95% confidence interval [CI]: 0.29-0.56; p < .0001 for overall mortality and OR 0.32, 95% CI: 0.18-0.57; p < .001 for SUDEP). Limited data are available regarding the risk of death and SUDEP in patients undergoing neuromodulation therapies, although some evidence indicates that vagus nerve stimulation might be associated with a lower risk of SUDEP. Several key questions remain to be addressed in future studies, considering the need to better inform patients about the long-term benefit-risk ratio of epilepsy surgery. Dedicated long-term prospective studies will thus be required to provide more personalized information on the impact of surgery and/or neuromodulation on the risk of death and SUDEP.

Strategic targeting of the temporal lobe with orthogonal placement of RNS leads

Responsive neurostimulation (RNS) is an effective treatment modality for refractory temporal lobe epilepsy (TLE). However, the optimal placement of RNS leads is not known. We use an orthogonal approach to lead placement instead of the more common longitudinal approach to target the entorhinal cortex (EC) given its potential for modulating activity entering and leaving the hippocampus. An orthogonal approach allows for coverage of the EC as well as the anterior lateral temporal cortex, which may be particularly beneficial for patients with mesial-lateral TLE and may also enable greater modulation of the limbic network. The objective of this study was to determine treatment outcomes for orthogonally placed RNS depth leads targeting the entorhinal cortex. We performed a retrospective analysis of prospectively collected data on a cohort of 13 patients. Mean follow-up duration was 57.3 months and the 50% responder rate was 76.9%. These results show that orthogonally placed RNS leads are safe and effective for the treatment of refractory TLE. Larger cohorts are needed to further delineate the clinical utility of this novel targeting strategy.

Surgery procedures in temporal lobe epilepsies

Temporal lobe epilepsy (TLE) is the most common cause of refractory epilepsy amenable for surgical treatment and seizure control. Surgery for TLE is a safe and effective strategy. The seizure-free rate after surgical resection in patients with mesial or neocortical TLE is about 70%. Resective surgery has an advantage over stereotactic radiosurgery in terms of seizure outcomes for mesial TLE patients. Both techniques have similar results for safety, cognitive outcomes, and associated costs. Stereotactic radiosurgery should therefore be seen as an alternative to open surgery for patients with contraindications for or with reluctance to undergo open surgery. Laser interstitial thermal therapy (LITT) has also shown promising results as a curative technique in mesial TLE but needs to be more deeply evaluated. Brain-responsive stimulation represents a palliative treatment option for patients with unilateral or bilateral MTLE who are not candidates for temporal lobectomy or who have failed a prior mesial temporal lobe resection. Overall, despite the expansion of innovative techniques in recent years, resective surgery remains the reference treatment for TLE and should be proposed as the first-line surgical modality. In the future, ultrasound therapies could become a credible therapeutic option for refractory TLE patients.

Surgical Considerations of Intractable Mesial Temporal Lobe Epilepsy

Surgery of temporal lobe epilepsy is the best opportunity for seizure freedom in medically intractable patients. The surgical approach has evolved to recognize the paramount importance of the mesial temporal structures in the majority of patients with temporal lobe epilepsy who have a seizure origin in the mesial temporal structures. For those individuals with medically intractable mesial temporal lobe epilepsy, a selective amygdalohippocampectomy surgery can be done that provides an excellent opportunity for seizure freedom and limits the resection to temporal lobe structures primarily involved in seizure genesis.

Medial temporal lobe epilepsy associated with hippocampal sclerosis is a distinctive syndrome

Epileptic syndromes are distinctive disorders with specific features, which when taken together, permit a specific diagnosis. There is actually a debate on that medial temporal lobe epilepsy with hippocampal sclerosis is an epileptic syndrome. To address this issue, we searched for discriminative semiological features between temporal lobe epilepsy patients with hippocampal sclerosis (TLE-HS patients or group 1), TLE patients with medial structural lesion other than hippocampal sclerosis or in MRI-negative cases with medial onset on further investigations (group 2) and lateral TLE patients (LTLE or group 3). We retrospectively collected data from medical and EEG-video records of 523 TLE patients, referred for surgery to the Pitié-Salpêtrière Epileptology Unit between 1991 and 2014. We identified 389 patients belonging to group 1, 61 patients belonging to group 2, and 73 patients belonging to group 3 and performed a comparative analysis of their clinical data and surgical outcomes. TLE-HS patients (group 1): (1) began epilepsy earlier (11 ± 9 vs. 20 ± 10 vs. 15 ± 9 years); (2) exhibited more frequently early febrile convulsions (FC) (59 vs 7 vs 5%); (3) presented more: ictal gestural automatisms (90 vs 54 vs 67%), dystonic posturing (47 vs 20 vs 23%), and secondary generalized tonic-clonic seizures (GTCS) (70 vs 44% vs 48%) as compared to both groups 2 and 3 patients (all p < 0.001). With respect to auras, abdominal visceral auras were more reported by TLE-HS than by LTLE patients (49 vs 16%). Three cardinal criteria correctly classified 94% of patients into TLE-HS group: history of FC, dystonic posturing, and secondary GTCS. Postoperative outcome was significantly better in TLE-HS group than in the two other groups (p = 0.03 and 0.003). Our study demonstrates that cardinal criteria are reliably helpful to distinguish patients with TLE-HS from those with other TLE and may allow considering TLE-HS as a distinctive syndrome.

Focal drug-resistant epilepsy: Progress in care and barriers, a Morroccan perspective

INTRODUCTION

The aim of this study is to determine the clinical, paraclinical, therapeutic and outcome aspects of drug resistant patients with epilepsy in our region and consequently to discuss methods that may improve the management of these patients.

PATIENTS AND METHODS

This paper presents a retrospective study of 25 adult patients that were followed for focal drug resistant epilepsy in epileptology unit of the University Hospital of Fez, Morocco.

RESULTS

This study recorded 25 patients including 48% of males and 52% of females. The mean age of patients was 24years-old. Hippocampal sclerosis was present in 28.5% of patients (7 cases); brain malformations were found in 19% of patients (5 cases); tumors were found in 24% of patients (6 cases); post-traumatic, post-surgical and anoxic-ischemic lesions were found in 28.5% of patients (7 cases). Resective epilepsy surgery was performed in 28,5% of patients (7 cases). Post surgical outcome was good for 5/7 patients (Engel I and II).

CONCLUSION

The clinical characteristics, etiologies and clinical course of medically refractory focal epilepsy in our region are similar to that reported in the global literature. We also demonstrated a long delay between onset of seizures and surgery (15years range 8-34years) and barriers to epilepsy surgery.

Differences between mesial and neocortical magnetic-resonance-imaging-negative temporal lobe epilepsy

OBJECTIVE

The aim of this study was to assess clinical and electrophysiological differences within a group of patients with magnetic-resonance-imaging-negative temporal lobe epilepsy (MRI-negative TLE) according to seizure onset zone (SOZ) localization in invasive EEG (IEEG).

METHODS

According to SOZ localization in IEEG, 20 patients with MRI-negative TLE were divided into either having mesial SOZ-mesial MRI-negative TLE or neocortical SOZ-neocortical MRI-negative TLE. We evaluated for differences between these groups in demographic data, localization of interictal epileptiform discharges (IEDs), and the ictal onset pattern in semiinvasive EEG and in ictal semiology.

RESULTS

Thirteen of the 20 patients (65%) had mesial MRI-negative TLE and 7 of the 20 patients (35%) had neocortical MRI-negative TLE. The differences between mesial MRI-negative TLE and neocortical MRI-negative TLE were identified in the distribution of IEDs and in the ictal onset pattern in semiinvasive EEG. The patients with neocortical MRI-negative TLE tended to have more IEDs localized outside the anterotemporal region (p=0.031) and more seizures without clear lateralization of ictal activity (p=0.044). No other differences regarding demographic data, seizure semiology, surgical outcome, or histopathological findings were found.

CONCLUSIONS

According to the localization of the SOZ, MRI-negative TLE had two subgroups: mesial MRI-negative TLE and neocortical MRI-negative TLE. The groups could be partially distinguished by an analysis of their noninvasive data (distribution of IEDs and lateralization of ictal activity). This differentiation might have an impact on the surgical approach.

Neuroimaging for patient selection for medial temporal lobe epilepsy surgery: Part 1 Structural neuroimaging

The objective of part one of this review is to present the structural neuroimaging techniques that are currently used to evaluate patients with temporal lobe epilepsy (TLE), and to discuss their potential to define patient eligibility for medial temporal lobe surgery. A PubMed query, using Medline and Embase, and subsequent review, was performed for all English language studies published after 1990, reporting neuroimaging methods for the evaluation of patients with TLE. The extracted data included demographic variables, population and study design, imaging methods, gold standard methods, imaging findings, surgical outcomes and conclusions. Overall, 56 papers were reviewed, including a total of 1517 patients. This review highlights the following structural neuroimaging techniques: MRI, diffusion-weighted imaging, tractography, electroencephalography and magnetoencephalography. The developments in neuroimaging during the last decades have led to remarkable improvements in surgical precision, postsurgical outcome, prognosis, and the rate of seizure control in patients with TLE. The use of multiple imaging methods provides improved outcomes, and further improvements will be possible with future studies of larger patient cohorts.

Childhood temporal lobe epilepsy: correlation between electroencephalography and magnetic resonance spectroscopy: a case-control study

Background

The diagnosis of epilepsy should be made as early as possible to give a child the best chance for treatment success and also to decrease complications such as learning difficulties and social and behavioral problems. In this study, we aimed to assess the ability of magnetic resonance spectroscopy (MRS) in detecting the lateralization side in patients with Temporal lobe epilepsy (TLE) in correlation with EEG and MRI findings.

Methods

This was a case–control study including 40 patients diagnosed (clinically and by EEG) as having temporal lobe epilepsy aged 8 to 14 years (mean, 10.4 years) and 20 healthy children with comparable age and gender as the control group. All patients were subjected to clinical examination, interictal electroencephalography and magnetic resonance imaging (MRI). Proton magnetic resonance spectroscopic examination (MRS) was performed to the patients and the controls.

Results

According to the findings of electroencephalography, our patients were classified to three groups: Group 1 included 20 patients with unitemporal (lateralized) epileptic focus, group 2 included 12 patients with bitemporal (non-lateralized) epileptic focus and group 3 included 8 patients with normal electroencephalography. Magnetic resonance spectroscopy could lateralize the epileptic focus in 19 patients in group 1, nine patients in group2 and five patients in group 3 with overall lateralization of (82.5%), while electroencephalography was able to lateralize the focus in (50%) of patients and magnetic resonance imaging detected lateralization of mesial temporal sclerosis in (57.5%) of patients.

Conclusion

Magnetic resonance spectroscopy is a promising tool in evaluating patients with epilepsy and offers increased sensitivity to detect temporal pathology that is not obvious on structural MRI imaging.

Functional neuroimaging findings in patients with lateral and mesio-lateral temporal lobe epilepsy; FDG-PET and ictal SPECT studies

The differentiation of combined mesial and lateral temporal onset of seizures (mesio-lateral TLE, MLTLE) from lateral TLE (LTLE) is critical to achieve good surgical outcomes. However, the functional neuroimaging features in LTLE patients based on the ictal onset zone utilizing intracranial EEG (iEEG) in a large series have not been investigated. We enrolled patients diagnosed with MLTLE (n = 35) and LTLE (n = 53) based on the site of ictal onset zone from iEEG monitoring. MLTLE is defined when ictal discharges originate from the mesial and lateral temporal cortices independently, whereas seizures of LTLE arise exclusively from the lateral temporal cortex. Compared to patients with LTLE, patients with MLTLE were more likely to have 18F- fluorodeoxyglucose positron emission tomography (FDG-PET) hypometabolism and hyperperfusion on ictal single-photon emission computed tomography (SPECT) restricted to the temporal areas. MLTLE patients had more frequent aura or secondarily generalized seizures than LTLE patients. No significant differences were found in scalp EEG, MRI, and Wada asymmetry between groups. The overall seizure-free rate was good (73.8%, mean follow-up = 9.7 years), which was not different (Engel class I, 74.3% in MLTLE vs. 73.6% in LTLE). Postsurgical memory function was spared in LTLE patients, while visual memory was impaired in MLTLE patients when their mesial temporal structures were sufficiently resected. It suggests that functional neuroimaging (interictal PET and ictal and interictal SPECT) may play a crucial role to differentiate between MLTLE and LTLE.

Pediatric temporal lobe epilepsy surgery: resection based on etiology and anatomical location

Advances in electrophysiological assessment with improved structural and functional neuroimaging have been very helpful in the use of surgery as a tool for drug-resistant epilepsy. Increasing interest in epilepsy surgery has had a major impact on adult patients; a refined evaluation process and new criteria for drug resistance combined with refined surgical techniques resulted in large surgical series in many centers. Pediatric surgery has lagged behind this evolution, possibly because of the diverse semiology and electrophysiology of pediatric epilepsy obscuring the focal nature of the seizures and frustrating the treatment of catastrophic epileptic syndromes specific to children. Unfortunately, refractory -epilepsy is more -devastating in children than in adults as it interferes with all aspects of neural development. Nevertheless, during the last few decades, the efforts of a small number of centers with encouraging results in pediatric epilepsy surgery have motivated pediatric neurologists to gain interest. Although well behind in the number of patients compared with that of adults, pediatric series are increasing exponentially. While temporal lobe epilepsy is the focus of interest in adults, with almost 70 % of resections in the temporal lobe, the pediatric epilepsy spectrum is different. Resective or functional surgery techniques devoted to resistant extratemporal epilepsy are the major improvements in pediatric epilepsy surgery. Temporal lobe epilepsy in adults has been studied extensively but only recently has begun to receive attention in children. Several aspects of temporal lobe epilepsy in childhood remain unclear or controversial in terms of seizure semiology and its pathology. This is reflected in the surgical treatment. Information on the major contributors to a favorable outcome, such as type or extent of resection, in terms of seizure control and morbidity is not available as in adult temporal lobe epilepsy. This chapter discusses the major discrepancies between adult and pediatric temporal lobe epilepsy and outlines the current concepts in surgical treatment. The resection strategy based on the different substrates at different locations in the temporal lobe causing seizures is emphasized with respect to available literature.

Neocortical temporal lobe epilepsy

Complex partial seizures (CPSs) can present with various semiologies, while mesial temporal lobe epilepsy (mTLE) is a well-recognized cause of CPS, neocortical temporal lobe epilepsy (nTLE) albeit being less common is increasingly recognized as separate disease entity. Differentiating the two remains a challenge for epileptologists as many symptoms overlap due to reciprocal connections between the neocortical and the mesial temporal regions. Various studies have attempted to correctly localize the seizure focus in nTLE as patients with this disorder may benefit from surgery. While earlier work predicted poor outcomes in this population, recent work challenges those ideas yielding good outcomes in part due to better localization using improved anatomical and functional techniques. This paper provides a comprehensive review of the diagnostic workup, particularly the application of recent advances in electroencephalography and functional brain imaging, in neocortical temporal lobe epilepsy.

Temporal lobe epilepsy surgery failures: a review

Patients with temporal lobe epilepsy (TLE) are refractory to antiepileptic drugs in about 30% of cases. Surgical treatment has been shown to be beneficial for the selected patients but fails to provide a seizure-free outcome in 20–30% of TLE patients. Several reasons have been identified to explain these surgical failures. This paper will address the five most common causes of TLE surgery failure (a) insufficient resection of epileptogenic mesial temporal structures, (b) relapse on the contralateral mesial temporal lobe, (c) lateral temporal neocortical epilepsy, (d) coexistence of mesial temporal sclerosis and a neocortical lesion (dual pathology); and (e) extratemporal lobe epilepsy mimicking TLE or temporal plus epilepsy. Persistence of epileptogenic mesial structures in the posterior temporal region and failure to distinguish mesial and lateral temporal epilepsy are possible causes of seizure persistence after TLE surgery. In cases of dual pathology, failure to identify a subtle mesial temporal sclerosis or regions of cortical microdysgenesis is a likely explanation for some surgical failures. Extratemporal epilepsy syndromes masquerading as or coexistent with TLE result in incomplete resection of the epileptogenic zone and seizure relapse after surgery. In particular, the insula may be an important cause of surgical failure in patients with TLE.

Experimental models of seizures and epilepsies

Epilepsy is one of the most common neurological conditions that affect people of all ages. Epilepsy is characterized by occurrence of spontaneous recurrent seizures. Currently available drugs are ineffective in controlling seizures in approximately one-third of patients with epilepsy. Moreover, these drugs are associated with adverse effects, and none of them are effective in preventing development of epilepsy following an insult or injury. To develop an effective therapeutic strategy that can interfere with the process of development of epilepsy (epileptogenesis), it is crucial to study the changes that occur in the brain after an injury and before epilepsy develops. It is not possible to determine these changes in human tissue for obvious ethical reasons. Over the years, experimental models of epilepsies have contributed immensely in improving our understanding of mechanism of epileptogenesis as well as of seizure generation. There are many models that replicate at least some of the characteristics of human epilepsy. Each model has its advantages and disadvantages, and the investigator should be aware of this before selecting a specific model for his/her studies. Availability of a good animal model is a key to the development of an effective treatment. Unfortunately, there are many epilepsy syndromes, specifically pediatric, which still lack a valid animal model. It is vital that more research is done to develop animal models for such syndromes.

"MRI-negative PET-positive" temporal lobe epilepsy: invasive EEG findings, histopathology, and postoperative outcomes

The aim of this retrospective study was to analyze invasive EEG findings, histopathology, and postoperative outcomes in patients with MRI-negative, PET-positive temporal lobe epilepsy (TLE) (MRI-/PET+TLE) who had undergone epilepsy surgery. We identified 20 patients with MRI-/PET+TLE (8.4% of all patients with TLE who had undergone surgery; 11 men, 9 women). Of the 20 patients, 16 underwent invasive EEG. The temporal pole and hippocampus were involved in the seizure onset zone in 62.5% of the patients. We did not identify a lateral temporal or extratemporal seizure onset in any patient. Of the 20 patients, 17 had follow-up periods >1 year (mean follow-up=3.3 years). At the final follow-up, 70.6% patients were classified as Engel I, 5.8% of patients as Engel II, and 11.8% of patients as Engel III and IV (11.8%). Histopathological evaluation showed no structural pathology in any resected hippocampus in 58% of all evaluated temporal poles. The most common pathology of the temporal pole was focal cortical dysplasia type IA or IB. MRI-/PET+TLE should be delineated from other "nonlesional TLE." The ictal onset in these patients was in each case in the temporal pole or hippocampus, rather than in the lateral temporal neocortex. Standard surgery produced a good postoperative outcome, comparable to that for patients with lesional TLE. Histopathological findings were limited: the most common pathology was focal cortical dysplasia type I.

The value of intraoperative electrocorticography in surgical decision making for temporal lobe epilepsy with normal MRI

PURPOSE

We hypothesized that acute intraoperative electrocorticography (ECoG) might identify a subset of patients with magnetic resonance imaging (MRI)-negative temporal lobe epilepsy (TLE) who could proceed directly to standard anteromesial resection (SAMR), obviating the need for chronic electrode implantation to guide resection.

METHODS

Patients with TLE and a normal MRI who underwent acute ECoG prior to chronic electrode recording of ictal onsets were evaluated. Intraoperative interictal spikes were classified as mesial (M), lateral (L), or mesial/lateral (ML). Results of the acute ECoG were correlated with the ictal-onset zone following chronic ECoG. Onsets were also classified as "M,""L," or "ML." Positron emission tomography (PET), scalp-EEG (electroencephalography), and Wada were evaluated as adjuncts.

KEY FINDINGS

Sixteen patients fit criteria for inclusion. Outcomes were Engel class I in nine patients, Engel II in two, Engel III in four, and Engel IV in one. Mean postoperative follow-up was 45.2 months. Scalp EEG and PET correlated with ictal onsets in 69% and 64% of patients, respectively. Wada correlated with onsets in 47% of patients. Acute intraoperative ECoG correlated with seizure onsets on chronic ECoG in all 16 patients. All eight patients with "M" pattern ECoG underwent SAMR, and six (75%) experienced Engel class I outcomes. Three of eight patients with "L" or "ML" onsets (38%) had Engel class I outcomes.

SIGNIFICANCE

Intraoperative ECoG may be useful in identifying a subset of patients with MRI-negative TLE who will benefit from SAMR without chronic implantation of electrodes. These patients have uniquely mesial interictal spikes and can go on to have improved postoperative seizure-free outcomes.

Stereotactic electroencephalography with temporal grid and mesial temporal depth electrode coverage: does technique of depth electrode placement affect outcome?

OBJECT

Intracranial monitoring for temporal lobe seizure localization to differentiate neocortical from mesial temporal onset seizures requires both neocortical subdural grids and hippocampal depth electrode implantation. There are 2 basic techniques for hippocampal depth electrode implantation. This first technique uses a stereotactically guided 8-contact depth electrode directed along the long axis of the hippocampus to the amygdala via an occipital bur hole. The second technique involves direct placement of 2 or 3 4-contact depth electrodes perpendicular to the temporal lobe through the middle temporal gyrus and overlying subdural grid. The purpose of this study was to determine whether one technique was superior to the other by examining monitoring success and complications.

METHODS

Between 1997 and 2005, 41 patients underwent invasive seizure monitoring with both temporal subdural grids and depth electrodes placed in 2 ways. Patients in Group A underwent the first technique, and patients in Group B underwent the second technique.

RESULTS

Group A consisted of 26 patients and Group B 15 patients. There were no statistically significant differences between Groups A and B regarding demographics, monitoring duration, seizure localization, or outcome (Engel classification). There was a statistically significant difference at the point in time at which these techniques were used: Group A represented more patients earlier in the series than Group B (p < 0.05). The complication rate attributable to the grids and depth electrodes was 0% in each group. It was more likely that the depth electrodes were placed through the grid if there was a prior resection and the patient was undergoing a new evaluation (p < 0.05). Furthermore, Group A procedures took significantly longer than Group B procedures.

CONCLUSIONS

In this patient series, there was no difference in efficacy of monitoring, complications, or outcome between hippocampal depth electrodes placed laterally through temporal grids or using an occipital bur hole stereotactic approach. Placement of the depth electrodes perpendicularly through the grids and middle temporal gyrus is technically more practical because multiple head positions and redraping are unnecessary, resulting in shorter operative times with comparable results.

Long-term follow-up outcome after surgical treatment for lesional temporal lobe epilepsy

OBJECTIVES

Lateral or neocortical temporal lobe epilepsy (TLE) is regarded as a distinct clinical entity from medial TLE. Surgery for neocortical TLE can be considered as a viable treatment option; however, there is very limited information available on aspects such as long-term seizure outcome. Thus, we retrospectively reviewed our ten surgical cases of lateral TLE with a minimum 2 year follow-up outcome.

METHODS

The series comprised four male and six female patients, ranging in age from 3 to 46 years (mean: 28.8 years). Seven cases were found to be drug-resistant. Invasive pre-surgical evaluation for intractable epilepsy was performed in six patients.

RESULTS

The pathologic lesions were removed completely in nine cases. Lesionectomy alone was performed in four cases and total epileptogenic focus resection was confirmed in four cases. The epileptogenic regions within eloquent areas were preserved in two cases. The medial temporal structure was intact and preserved in all cases. Neuropathologic diagnoses were cavernoma in three cases, astrocytoma (grade 2) in two cases, arteriovenous malformation in two cases, gliosis in two cases and ganglioglioma in one case. The mean duration of follow-up was 6.5 years (range: 2.2-9.3 years). Outcomes categorized according to Engel classes were class I (E1) in six cases and class II (E2) in four cases. Patients who had post-operative seizures may also achieve long-term seizure decrease or freedom in three cases: case 5 (E4-E2), case 6 (E4-E2) and case 7 (E3-E1). Thus, worthwhile improvement was achieved in 100% of the cases in this series, with 60% of patients being seizure-free during the followed-up period.

CONCLUSIONS

The controlled long-term follow-up results suggested that surgery for lesional TLE can be considered as a viable treatment option to control seizure with a low morbidity rate and good outcomes.

Temporal lobe surgery in patients with normal MRI

PURPOSE OF REVIEW

The surgical approach to nonlesional temporal lobe epilepsy presents a significant challenge due to uncertainties regarding the extent of resection necessary to result in a seizure-free state. To outline an optimum surgical strategy, an understanding of the clinical and diagnostic presentation of mesial and lateral temporal epilepsy is required in order to properly characterize the location of the ictal onset zone. This review focuses on several methods used to identify this ictal onset zone, with emphasis on the impact each modality has on surgical outcome.

RECENT FINDINGS

Factors predicting an excellent surgical outcome include the presence of a discrete zone of low voltage fast activity and prolonged propagation time on the electroencephalogram, and the absence of metabolic dysfunction in the contralateral temporal lobe. Identifying epileptogenic regions in the temporal lobe using magnetic source imaging is a recent technique that has also yielded promising surgical outcomes. Recent prospective studies have shown that a temporal neocortical resection is very effective in providing a seizure free outcome given strict localization of the ictal onset zone to the lateral temporal region, highlighting the need for accurate characterization of mesial versus lateral nonlesional epilepsy.

SUMMARY

With accurate identification of the ictal onset zone with intracranial electroencephalography, a tailored temporal resection can yield excellent surgical results.

The localization and lateralization of memory deficits in children with temporal lobe epilepsy

PURPOSE

It is often reported that children with temporal lobe epilepsy (TLE) experience nonlateralized memory impairments. However, many of these studies have been exploratory and not based on memory theory. Further, differences between mesial and lateral subgroups have not been adequately examined. This study aimed to discern more specific patterns of memory impairment in children with TLE.

METHODS

Forty-three children (5-16 years) with lesional TLE participated. Subjects were categorized in terms of lesion laterality (left, n = 21; right, n = 22) and intratemporal location (mesial, n = 31; lateral, n = 12). Verbal and nonverbal memory tasks were administered that reflected associative, allocentric and recognition paradigms.

RESULTS

Facial recognition was poorer in right TLE (p = 0.03). There were no differences between left and right groups on any other memory task, even when comparisons were restricted to cases with mesial involvement. Irrespective of laterality, clear differences were observed between mesial and lateral lesion subgroups (arbitrary associative learning, p = 0.01; complex figure recall, p = 0.03). The lateral lesion subgroup displayed intact memory function relative to normative standards.

CONCLUSIONS

Memory is more frequently impaired in children with mesial as opposed to lateral TLE. Tasks with an associative component discriminated between these subgroups, supporting an associative model of hippocampal function. With the exception of facial recognition, memory deficits were not lateralized. Therefore, the nature of memory impairment experienced by children with TLE cannot be extrapolated from adult models.

Tailored anteromedial lobectomy in the treatment of refractory epilepsy of the temporal lobe: Long term surgical outcome and predictive factors

OBJECTIVE

To analyze long-term results and to determine prognostic factors on seizure outcome in a series of patients with temporal lobe epilepsy (TLE) who underwent anteromedial temporal lobectomy (AMTL).

MATERIALS AND METHODS

From 1995 to 1998 forty-two patients suffering from non-lesional TLE underwent tailored AMTL at our Institution. We retrospectively reviewed surgical results and calculated predictive factors of good outcome in the long term.

RESULTS

Sixty-four percent of patients were rendered seizure free (median follow up 60 months). Eleven cases (26.2%) had a significant reduction of disabling epileptic episodes. Poor seizure control was observed in four patients (9.5%). Overall surgical morbidity was 4.7%. Medial temporal sclerosis (MTS) was the most common histopathological finding (69% of cases). The presence of unilateral hippocampal abnormalities on qualitative MRI was significantly associated with excellent postoperative outcome (p<0.011). Qualitative preoperative MRI had a positive predictive value of 83% in detecting both MTS at pathological examination and excellent outcome.

CONCLUSIONS

Tailored AMTL is a safe and effective procedure in the treatment of selected patients with medically refractory TLE. Data from preoperative qualitative MRI well correlated with histopathological findings. The presence of unilateral hippocampal atrophy on qualitative MRI was predictive of excellent outcome in the long-term follow up.

Clinico-electrical Characteristics of Lateral Temporal Lobe Epilepsy; Anterior and Posterior Lateral Temporal Lobe Epilepsy

BACKGROUND AND PURPOSE

This study aimed to determine whether there are clinicoelectrical differences between anterior lateral temporal lobe epilepsy (ALTLE) and posterior lateral temporal lobe epilepsy (PLTLE), taking medial temporal lobe epilepsy (MTLE) as a reference.

METHODS

We analyzed the historical information, ictal semiologies, and ictal EEGs of temporal lobe epilepsy patients with a documented favorable surgical outcome (Engel class I or II) at follow-up after more than one year. LTLE was defined when a discrete lesion on MRI or an ictal onset zone in invasive study was located outside the collateral sulcus. LTLE was further divided into ALTLE and PLTLE by reference to the line across the cerebral peduncle. Total 107 seizures of 13 ALTLE, 8 PLTLE and 21 MTLE patients were reviewed.

RESULTS

Initial hypomotor symptom was frequently observed in PLTLE (P<0.001). Oroalimentary automatism (OAA) was not observed initially in PLTLE. Generalized tonic-clonic seizures occurred significantly earlier in PLTLE than in ALTLE or MTLE (P< 0.001). Ictal scalp EEG was not helpful in differentiating between ALTLE and PLTLE.

CONCLUSIONS

Frequent hypomotor onset, the absence of initial oroalimentary automatism, and early generalization are characteristic findings of PLTLE, although they are insufficient to differentiate it from ALTLE or MTLE.

The clinical and electrophysiological characteristics of temporal lobe epilepsy with normal MRI

Background and Purpose

To identify the clinical and electrophysiological characteristics of temporal lobe epilepsy (TLE) with normal MRI.

Methods

Twenty-six patients were diagnosed with TLE with normal MRI by stereotaxically implanted depth electrode EEG (SEEG) and quantitative MRI. We divided the patients into anterior or diffuse temporal groups by interictal EEG, into localized, hemispheric or non-lateralized onset groups by ictal scalp EEG, and into focal or regional onset groups by SEEG. The clinical and electrophysiological characteristics were compared with those of 25 TLE patients with unilateral hippocampal atrophy (HA) on MRI. Four patients of TLE with unilateral HA also underwent SEEG.

Results

Patients in the normal MRI group showed a significantly higher frequency of secondarily generalization (225±235, median 160 vs 68±48, median 50, p<0.05), shorter duration of epilepsy (16±10 yrs vs 25.9±7.8 yrs, p<0.001), and less favorable surgical outcome (50% vs 88%, p <0.05) than patients in the unilateral HA group. Also, patients with normal MRI frequently showed diffuse temporal (50% vs 20%, p<0.05) discharges on interictal EEG. The ictal seizure patterns of patients with normal MRI showed less localization to one temporal lobe on scalp EEG (28% vs 65%, p<0.001) and a higher frequency of regional onset on SEEG (68% vs 8%, p<0.001) than patients with unilateral HA.

Conclusions

The characteristics of TLE with normal MRI compared with TLE with unilateral HA are shorter duration of epilepsy, higher frequency of secondarily generalization, and less favorable surgical outcome, suggesting wider areas of temporal lobe involved compared with patients with unilateral HA.

Prognostic factors for surgery of neocortical temporal lobe epilepsy

OBJECTIVES

In the current classification of epilepsies two forms of temporal lobe epilepsy (TLE) were included: mesial and lateral (neocortical) TLE. We aimed at identifying prognostic factors for the surgical outcome of lesional neocortical TLE.

METHODS

We included consecutive patients who had undergone presurgical evaluation including ictal video-EEG and high-resolution MRI, who had TLE due to neocortical lateral epileptogenic lesions, who had a lesionectomy and who had >2-year follow-up.

RESULTS

There were 29 patients who met the inclusion criteria. Twenty of them became postoperatively seizure-free. Patients' mean age was 34.8+/-9 years (range 18-52). The age at epilepsy onset was 20.1+/-8 years. We found that left-sided surgery (p=0.048) and focal cortical dysplasia (FCD) on MRI (p=0.005) were associated with non-seizure-free outcome, while lateralized/localized EEG seizure pattern (p=0.032), tumors on the MRI (p=0.013), and a favorable seizure situation at the 6-month postoperative evaluation were associated with 2-year postoperative seizure-freedom (p<0.001). Multivariate analysis indicated that the side of surgery was not an independent predictor.

CONCLUSION

More than two-thirds of the patients with neocortical TLE became seizure-free postoperatively. Lateralized/localized EEG seizure pattern and tumors on the MRI were associated with postoperative seizure-freedom, while FCD were associated with a poor outcome. The 6-month postoperative outcome is a reliable predictor for the long-term outcome.

[Extra-hippocampal temporal lesions inducing symptomatic drug-resistant epilepsies. Which surgical procedure?]

In partial symptomatic epilepsy due to discrete brain lesion, total removal of the epileptogenic lesion generally yields major reduction of seizures, achieved in 85% of the patients. However, prognosis is worse in patients with symptomatic temporal lobe epilepsy. Implication of the temporo-mesial structures in the seizures genesis is generally considered. Careful electroclinical and radiological analysis can provide useful but insufficient information. In order to evaluate the criteria we used to guide our surgical strategy, we analyzed retrospectively a series of 47 patients with drug-resistant symptomatic extra hipocampic temporal epilepsy surgically treated either by isolated lesionectomy (group 1, n=17) or by resection of temporo-mesial structures and associated lesionectomy (group 2, n=30). Patients with extrahippocampal lesions and hippocampal sclerosis (dual pathology) were excluded from this study. With a mean follow-up of 72 months, overall results showed that 84% of group 2 patients (Engel's grade Ia) were seizure-free compared with only 47% of group 1 patients. Statistical analysis showed that the type of surgical procedure was the main prognostic factor. In conclusion, the optimal surgical procedure cannot be defined only with the criteria usually retained for temporo-mesial involvement in seizure genesis. Taking into account the prognostic value of such implication, although complex, is of paramount importance. Our results could be explained by the presence of an acquired dual functional pathology.

The Effects on Cognitive Performance of Tailored Resection in Surgery for Nonlesional Mesiotemporal Lobe Epilepsy

PURPOSE

Mesiotemporal lobe epilepsy (MTLE) can be treated with different surgical approaches. In tailored resections, neocortex is removed beyond "standard" margins when spikes are present in the electrocorticogram. We hypothesized that these larger resections are justified because spiking neocortex is dysfunctional. This would imply that in patients with spikes (a) postoperative cognitive performance is not affected, and (b) preoperative performance is worse than without spikes.

METHODS

We studied 80 operated-on MTLE patients with pathologically confirmed nonlesional hippocampal sclerosis. All patients were left-sided language dominant and underwent cognitive tests 6 months pre- and postoperatively. A repeated measures analysis of variance (ANOVA) was performed, looking for within- and between-subjects interactions with presence of intraoperative neocortical spikes.

RESULTS

Intraoperatively, neocortical spikes were present in 61% of patients. Improved postoperative cognitive outcome was seen only in left-sided patients with spikes. Their performance IQ (PIQ) increased by 8.1 points (95% confidence interval, 3.8-12.3; p = 0.02), and visual naming latency by 12.8 s (95% CI, 2.1-23.5; p = 0.07). Conversely, in left-sided patients without spikes, naming latency declined by 7.5 s (95% CI, -2.3-17.2; p = 0.07). Preoperative scores were comparable except for a 15.3-point (95% CI, 0.1-30.5; p = 0.02) lower VIQ in left-sided patients without spikes.

CONCLUSIONS

Tailoring does not harm cognitive performance and is, in left-sided MTLE, associated with postoperative improvement. Left-sided MTLE without neocortical spikes has lower verbal scores, which tend to decline after standard resection and may represent a special pathophysiologic entity.

Semiologic and electrophysiologic correlations in temporal lobe seizure subtypes

PURPOSE

The International League Against Epilepsy (ILAE) classification distinguishes medial and neocortical temporal lobe epilepsies. Among other criteria, this classification relies on the identification of two different electroclinical patterns, those of medial (limbic) and lateral (neocortical) temporal lobe seizures, depending on the structure initially involved in the seizure activity. Recent electrophysiologic studies have now identified seizures in which medial and neocortical structures are both involved at seizure onset. The purpose of the study was therefore to study the correlations of ictal semiology with the spatiotemporal pattern of discharge in temporal lobe seizures.

METHODS

The 187 stereoelectroencephalography-recorded seizures from 55 patients were analyzed. Patients were classified into three groups according to electrophysiologic findings: medial (M; seizure onset limited to medial structures, n=24), lateral (L; seizure onset limited to lateral structures, n=13), and medial-lateral (ML; seizure onset involving both medial and lateral structures, n=18). Clinical findings were compared between groups.

RESULTS

Initial epigastric sensation, initial fear, delayed oroalimentary and elementary upper limb automatisms, delayed loss of contact, long seizure duration, and absent or rare secondary generalizations were associated with M seizures. Initial auditory illusion or hallucination, initial loss of contact, shorter duration of seizures, and more frequent generalizations were associated with L seizures. Initial epigastric sensation, initial loss of contact, early oroalimentary and verbal automatisms, and long duration of seizures were associated with ML seizures.

CONCLUSIONS

Although the syndrome of mesial temporal epilepsy is now relatively well defined, our findings support the idea that the organization of temporal lobe seizures may be complex and that different patterns exist. We demonstrate three distinct patterns, characterized by both semiologic and electrophysiologic features. This distinction may help to define better the epileptogenic zone and the subsequent surgical procedure.

Use of intraoperative magnetic resonance imaging in tailored temporal lobe surgeries for epilepsy

PURPOSE

We investigated whether intraoperative magnetic resonance imaging (MRI) was able to assess immediately the extent of a tailored temporal lobe resection for epilepsy in comparison to delayed postoperative MRI. The recently proposed concept of an individually tailored procedure, preserving tissue not involved in seizures, leads to a variety of differently shaped resections.

METHODS

For intraoperative imaging we used a Magnetom Open 0.2 Tesla scanner. Fifty-eight patients undergoing temporal lobe resections for pharmacoresistant epilepsy were investigated. Half of these were nonlesional. All patients had delayed postoperative follow-up scans, which were compared with the intraoperative, postresection images.

RESULTS

In 49 (84%) of 58 cases, intraoperative MRI depicted the resection cavity identical to delayed postoperative studies. Complete resection of the visible lesion was primarily proved in 23 of the 29 cases. In two patients with lesions and in one nonlesional case, the resection was extended after intraoperative imaging, thus increasing the rate of total resections in gliomas from 73 to 87%. In four patients, an extension into eloquent areas did not allow complete removal. In the nonlesional cases (n = 29), the extent of tailored temporal resections also could be exactly documented intraoperatively.

CONCLUSIONS

Intraoperative MRI allowed a reliable evaluation of the localization and extent of resection in epilepsy surgery within the operative procedure. Furthermore, it provided the possibility of an image-based correction of an initially incomplete resection, particularly in lesional cases. In the majority of patients, the intraoperative images would have been able to replace delayed postoperative MRI. However, in 16%, there were postoperative changes in the resection volume.

Seizure outcome after temporal lobectomy: current research practice and findings

PURPOSE

The literature regarding seizure outcome and prognostic factors for outcome after temporal lobectomy is often contradictory. This is problematic, as these data are the basis on which surgical decisions and counseling are founded. We sought to clarify inconsistencies in the literature by critically examining the methods and findings of recent research.

METHODS

A systematic review of the 126 articles concerning temporal lobectomy outcome published from 1991 was conducted.

RESULTS

Major methodologic issues in the literature were heterogeneous definitions of seizure outcome, a predominance of cross-sectional analyses (83% of studies), and relatively short follow-up in many studies. The range of seizure freedom was wide (33-93%; median, 70%); there was a tendency for better outcome in more recent studies. Of 63 factors analyzed, good outcome appeared to be associated with several factors including preoperative hippocampal sclerosis, anterior temporal localization of interictal epileptiform activity, absence of preoperative generalized seizures, and absence of seizures in the first postoperative week. A number of factors had no association with outcome (e.g., age at onset, preoperative seizure frequency, and extent of lateral resection).

CONCLUSIONS

Apparently conflicting results in the literature may be explained by the methodologic issues identified here (e.g., sample size, selection criteria and method of analysis). To obtain a better understanding of patterns of long-term outcome, increased emphasis on longitudinal analytic methods is required. The systematic review of possible risk factors for seizure recurrence provides a basis for planning further research.

Neural networks involving the medial temporal structures in temporal lobe epilepsy

OBJECTIVES

In a previous study using the averaged coherence technique to study interactions between medial/limbic and lateral/neocortical regions, we observed that epileptogenic networks in temporal lobe epilepsy seizures (TLES) could be divided into 4 subtypes, i.e. medial (M), medial-lateral (ML), lateral-medial (LM), and lateral (L). In the ML and LM subtypes, medial structures and the anterior temporal neocortex are co-activated at the onset of seizures. However, using this approach, we were unable to determine the direction of coupling and may have overlooked non-linear variations in interdependency. The purpose of the present study using non-linear regression for analysis of stereoelectroencephalographic (SEEG) signal pairs was to measure the degree and direction of coupling between medial and neocortical areas during TLES in patients with the M, ML, and LM subtypes.

METHODS

Eighteen patients with drug-resistant TLEs who underwent SEEG recording were studied. We used a non-linear correlation method as a measure of the degree and the direction of coupling on SEEG signal pairs. Patients with pure lateral TLEs were not studied. We analyzed the functional coupling between 3 regions of the temporal lobe: the anterior temporal neocortex, the amygdala, and the anterior hippocampus. A physiological model of EEG generation was used to validate the non-linear quantification method and assess its applicability to real SEEG signals.

RESULTS

Results are first based on a physiological model of EEG data in which both degree and direction of coupling are explicitly represented, thus allowing construction of the neural systems inside which causality relationships are controlled and generation of multichannel EEG signals from these systems. These signals provide an objective way of studying the performance of non-linear regression analysis on real signals. In medial networks (10 patients), the ictal discharge is limited to the medial limbic structures and may propagate secondarily to the cortex. Quantified results demonstrated no significant coupling between medial and lateral structures at the beginning of the seizures. Conversely, almost constant unidirectional or bidirectional coupling was observed between hippocampus and amygdala. In medial-lateral (5 patients) and lateral-medial (3 patients) networks, the initial ictal discharge includes both limbic and neocortical regions. A rapid "tonic" discharge is observed over the temporal neocortex at the onset of seizure. Quantitative analysis showed an initial increase in the non-linear correlation coefficient between neocortex and medial structures. Quantification of the coupling direction demonstrated influence of medial over lateral structures (medial-lateral) or of the lateral neocortex over medial structures (lateral-medial).

CONCLUSIONS

These results confirm the existence of several generic and organized networks involving the medial structures during TLE seizures.

Long-term EEG monitoring: a clinical approach to electrophysiology

Long-term electroencephalographic monitoring (LTM) is the capability of recording the EEG over long periods of time and not a specific duration. Prolonged EEG recording is used primarily for epilepsy monitoring, but LTM is also used in the intensive care unit, the operating room, and in the emergency department. The purpose of LTM is to expand the limited time sampling associated with shorter "routine" EEG recording. Audiovisual monitoring may also be used in conjunction with LTM to evaluate simultaneously a specific clinical behavior that may or may not be associated with EEG alteration. This is typically performed in a hospital setting for safety and ancillary testing purposes. LTM is used most frequently in the diagnosis and management of seizures and "spells," but has also gained wider application in the evaluation of sleep disorders, cerebrovascular disease, psychiatric conditions, and movement disorders. Computer-assisted LTM systems that process, analyze, compress, and store data digitally have become widely available in clinical practice both in the hospital as well as outside the hospital when the patient is ambulatory.

Medically intractable, localization-related epilepsy with normal MRI: presurgical evaluation and surgical outcome in 43 patients

PURPOSE

High-resolution magnetic resonance imaging (MRI) plays a crucial role in the presurgical evaluation of patients with medically refractory partial epilepsy. Although MRI detects a morphologic abnormality as the cause of the epilepsy in the majority of patients, some patients have a normal MRI. This study was undertaken to explore the hypothesis that in patients with normal MRI, invasive monitoring can lead to localization of the seizure-onset zone and successful epilepsy surgery.

METHODS

A series of 115 patients with partial epilepsy who had undergone intracranial electrode evaluation (subdural strip, subdural grid, and/or depth electrodes) between February 1992 and February 1999 was analyzed retrospectively. Of these, 43 patients (37%) had a normal MRI.

RESULTS

Invasive monitoring detected a focal seizure onset in 25 (58%) patients, multifocal seizure origin in 12 (28%) patients, and in six patients, no focal seizure origin was found. Of the 25 patients with a focal seizure origin, cortical resection was performed in 24, of whom 20 (83%) had a good surgical outcome with respect to seizure control. Six of the 12 patients with multifocal seizure origin underwent other forms of epilepsy surgery (palliative cortical resection in two, anterior callosotomy in two, and vagal nerve stimulator placement in two).

CONCLUSIONS

Successful epilepsy surgery is possible in patients with normal MRIs, but appropriate presurgical evaluations are necessary. In patients with evidence of multifocal seizure origin during noninvasive evaluation, invasive monitoring should generally be avoided.

Surgical treatment for neocortical temporal lobe epilepsy: clinical and surgical aspects and seizure outcome

OBJECT

The goal of this paper was to describe the clinical and surgical aspects of a group of patients suffering from drug-resistant neocortical temporal lobe epilepsy (TLE), as well as seizure outcomes and factors affecting seizure outcomes in these patients.

METHODS

This study was based on data prospectively collected and retrospectively evaluated. Sixty-two patients with neocortical TLE constituted the study population. Only patients who underwent corticectomies, lesionectomies, lateral anterior lobe resections, and/or multiple subpial transections were included. The pathological areas resected in these patients could be separated into three groups composed of 35 neoplastic lesions, 23 nonneoplastic lesions, and three nonlesional areas. The mean duration of follow-up review in these patients was 21.9+/-14 months. Outcomes were categorized according to Engel classes. Class I was found in 79% of the patients and Class II in 11%. Invasive presurgical evaluation was performed in 43% of the patients. There were only temporary complications (3.3% surgical and 1.6% neurological) and no deaths. In summary, lesions confirmed on histological examination were rarely found in patients with neocortical TLE. Low-grade tumors were the most commonly found lesions in these patients and the most common tumor was ganglioglioma. Outcome was best for those patients with neoplastic lesions and was independent of the duration of their seizures. Outcome was little influenced by the type of resection performed and was found to be as good as that achieved in patients with mesial TLE.

CONCLUSIONS

These results demonstrate that the concept of lateral or neocortical TLE as a distinct entity is useful. Surgery for neocortical TLE can be considered a viable treatment option that is associated with a low morbidity rate and good outcomes.

Intraoperative magnetic resonance imaging in epilepsy surgery

The aim of this study was to investigate how intraoperative magnetic resonance imaging (MRI) can help in epilepsy surgery to asses immediately whether a resection or disconnection procedure is tailored to the individual needs of a patient, thus ideally meeting the treatment plan and enhancing the efficiency of the procedure. The recently proposed concept of an individually tailored procedure with as limited tissue removal as possible would support a more conservative resection than initially advocated by many centers; such limited removal would preserve as much brain as possible that is not necessarily epileptogenic or involved in propagation of seizures. For intraoperative imaging we used a Magnetom Open 0.2-T scanner located in our "twin-OR" in 61 patients with pharmacoresistant epilepsy. A three-dimensional sequence was used, allowing free slice reformatting. In the nonlesional cases (n = 32) the extent of the tailored temporal resection (n = 28) or callosotomy (n = 4) could be documented exactly. In the 29 lesional cases the complete resection was primarily proved in 23 patients. In three glioma patients a lesion that extended into eloquent areas did not allow for complete removal. A second look (n = 3) could increase the rate of total resection in the lesional cases from 79% to 90%. Intraoperative MRI allowed a reliable evaluation of the extent of resection or disconnection in epilepsy surgery within the operative procedure. It also provided the possibility of a second look in cases of incomplete resection, especially in the lesional cases. Increased knowledge of structure-function relationships as partially defined by intraoperative imaging may reduce the adverse neuropsychological sequelae of epilepsy surgery in the future.

Monoamine neurotransmitters in resected hippocampal subparcellations from neocortical and mesial temporal lobe epilepsy patients: in situ microvoltammetric studies

It is known that epilepsy patients diagnosed with neocortical temporal lobe epilepsy (NTLE), differ from those diagnosed with mesial temporal lobe epilepsy (MTLE), e.g., in hippocampal (HPC) pathology. In the present studies, we tested the hypothesis that NTLE and MTLE subtypes of human epilepsy might differ in regards to their HPC monoamine neurochemistry. Monoamine neurotransmitters were studied in separate signals and within s with semiderivative microvoltammetry, used in combination with stearate indicator, Ag-AgCl reference and stainless steel auxiliary microelectrodes. Anterior HPC specimens from the patients' epileptogenic zone, defined by electrocorticography, were resected neurosurgically from 13 consecutive patients with intractable temporal lobe epilepsy. Four patients were diagnosed with NTLE and nine with MTLE. The criteria for the diagnosis of NTLE versus MTLE was absence versus presence of HPC sclerosis, respectively, based on MRI examination of resected tissue. In addition, NTLE patients demonstrated seizure onset in anterolateral temporal neocortex on electroencephalography (EEG). HPC subparcellations studied were: (a) Granular Cells of the Dentate Gyrus (DG), (b) Polymorphic Layer of DG and (c) Pyramidal Layer: subfields, CA1 and CA2. Dopamine (DA), serotonin (5-HT), norepinephrine (NE) and ascorbic acid (AA) (co-factor in DA to NE synthesis), exhibited separate and characteristic half-wave potentials in millivolts. Each half-wave potential, i.e., the potential at which maximum current was generated, was experimentally established in vitro. Concentrations of neurotransmitters found in HPC subparcellations were interpolated from calibration curves derived in vitro from electrochemical detection of monoamines and AA in saline phosphate buffer. Significant differences between subtypes in concentration of monoamines were analyzed by the Mann Whitney rank sum test and those differences in probability distribution of monoamines were analyzed by the Fisher Exact test; in each case, P<0.01 was the criteria selected for determining statistical significance. DA concentrations were higher in NTLE compared with MTLE in each HPC subparcellation [P=0.037, 0.024 and 0.007, respectively (P<0.01)] and DA occurred more frequently in NTLE in the Pyramidal Layer [P=0.077 (P<0.01)]. AA was present in one NTLE patient. NE concentrations were higher in MTLE vs. NTLE in each subparcellation [P=0.012, 0.067 and 0.07, respectively (P<0.01)] and NE occurred more frequently in MTLE in Granular Cells of DG and Pyramidal Layer [P=0.052 and 0.014, respectively (P<0.01)]. In MTLE, NE concentrations in the CA1 subfield of the Pyramidal Layer were decreased vs. the CA2 subfield [P=0.063 (P<0.01)]. Serotonin was found in every HPC subparcellation of each subtype but 5-HT concentrations were higher in NTLE vs. MTLE in the Granular Cells of DG and the Pyramidal Layer (CA1 subfield) [P=0.076 and 0.095, respectively (P<0.01)]. Thus, this preliminary study showed that marked differences in HPC monoamine neurochemistry occurred in NTLE patients as compared with MTLE patients.

Oxygen desaturations triggered by partial seizures: implications for cardiopulmonary instability in epilepsy

PURPOSE

The occurrence of hypoxemia in adults with partial seizures has not been systematically explored. Our aim was to study in detail the temporal dynamics of this specific type of ictal-associated hypoxemia.

METHODS

During long-term video/EEG monitoring (LTM), patients underwent monitoring of oxygen saturation using a digital Spo2 (pulse oximeter) transducer. Six patients (nine seizures) were identified with oxygen desaturations after the onset of partial seizure activity.

RESULTS

Complex partial seizures originated from both left and right temporal lobes. Mean seizure duration (+/-SD) was 73 +/- 18 s. Mean Spo2 desaturation duration was 76 +/- 19 s. The onset of oxygen desaturation followed seizure onset with a mean delay of 43 +/- 16 s. Mean (+/-SD) Spo2 nadir was 83 +/- 5% (range, 77-91%), occurring an average of 35 +/- 12 s after the onset of the desaturation. One seizure was associated with prolonged and recurrent Spo2 desaturations.

CONCLUSIONS

Partial seizures may be associated with prominent oxygen desaturations. The comparable duration of each seizure and its subsequent desaturation suggests a close mechanistic (possibly causal) relation. Spo2 monitoring provides an added means for seizure detection that may increase LTM yield. These observations also raise the possibility that ictal ventilatory dysfunction could play a role in certain cases of sudden unexpected death in epilepsy in adults with partial seizures.

Seizures of temporal lobe epilepsy: identification of subtypes by coherence analysis using stereo-electro-encephalography

OBJECTIVES

Two subtypes of temporal lobe epilepsy (TLE) according to the structures initially involved during seizures are currently recognized: medial TLE (MTLE) and lateral (or neocortical) TLE (LTLE). A few reports have suggested that the classification of TLE subtypes might be larger according to variations in the interactions between medial structures and the neocortex. In this study, we analyzed these interactions using coherence analysis of stereo-encephalographic (SEEG) signals during spontaneous seizures.

METHODS

Twenty-seven patients with drug-resistant TLE, diagnosed from ictal SEEG recordings obtained during pre-surgical evaluation, were studied. Orthogonally implanted depth electrodes with multiple leads according to Talairach's method were used to sample medial and neocortical structures. Coherence analysis of ictal discharges was performed between two SEEG bipolar signals from adjacent leads located either in medial structures (amygdala and hippocampus) or in neocortical regions of the temporal lobe. A new algorithm, which was designed to reduce the bias inherent in coherence estimation, was used to compute the coherence.

RESULTS

We were able to classify TLE seizures (TLES) into 4 distinct categories: (1) 'medial' TLES, characterized by medial onset with later involvement of the neocortex in the form of a 'phasic' discharge. High ictal coherence values were observed between medial structures; (2) 'medial-lateral' TLES which started in medial structures with a fast low-voltage discharge (FLVD) which rapidly affects the neocortex (< or = 3 s). High coherence values were observed between medial and lateral structures; (3) 'lateral-medial' TLES, which are different from medial-lateral TLES in that the FLVD starts in the lateral neocortex and involves the amygdala and/or hippocampus almost immediately after; (4) 'lateral' TLES: characterized by a neocortical onset, a delayed involvement of medial structures (when present), and high coherence values between neocortical structures.

CONCLUSIONS

These results demonstrate the existence of numerous interactions between medial limbic structures and the neocortex during TLE seizures. Such findings could have implications for surgical strategies and the prognosis of epilepsy surgery, particularly when limited resection is indicated.

Neocortical temporal lobe epilepsy: intracranial EEG features and surgical outcome

Patients with neocortical temporal lobe epilepsy (NTLE) may have less favorable outcome with anterior temporal lobectomy than those with mesial temporal foci. The authors analyzed ictal intracranial electroencephalograms (EEGs) in patients with NTLE to identify features that predict surgical outcome. The following intracranial ictal EEG features in 31 consecutive medically intractable NTLE patients were studied: Frequency (i.e., low-voltage fast [>20 Hz], recruiting ictal-onset spikes, ictal-onset rhythms less than 5 Hz, ictal-onset rhythms with repetitive sharp waves between 5 and 20 Hz); extent of ictal onset (focal, sublobar, and lobar); localization within the temporal lobe (anterior, posterior, or regional); and the time to seizure spread outside the temporal lobe (rapid, intermediate, and slow). The average follow-up period was 36.7 months (range, 18 to 60 months). Findings between two outcome groups were compared: class I group (seizure-free) and class II to IV group (persistent seizures). Twenty-one (66.7%) of 31 patients with NTLE were seizure-free. Intracranial EEG features which were significantly associated with seizure-free outcome were focal or sublobar onset, anterior temporal onset, and slow propagation time (P < 0.05). There was a trend for patients with ictal onset morphologies of slow ictal-onset rhythm and repetitive sharp waves to be seizure-free (P = 0.07). Intracranial EEG is helpful in predicting surgical outcome in NTLE patients.

Intracranial EEG in temporal lobe epilepsy

Intracranial EEG monitoring before epilepsy surgery, while becoming less commonly performed in patients with unilateral mesial temporal lobe epilepsy, is still widely used when bilateral independent temporal lobe seizures are suspected or when extratemporal foci cannot be ruled out by noninvasive means. Additionally, many epilepsy centers are reporting excellent surgical outcome in patients with neocortical temporal lobe epilepsy, when resections are guided by intracranial EEG studies. This article reviews the indications, technical aspects, risks, and interpretation of intracranial EEG in patients with temporal lobe seizures. It also considers intracranial EEG features predictive of surgical outcome.

Clinical patterns of patients with temporal lobe epilepsy and pure amygdalar atrophy

PURPOSE

MRI volumetric measurements (MRIvol) have been proven reliable in determining mesial temporal atrophy in patients with TLE. We attempted to correlate the clinical features with different patterns of hippocampal formation (HF) and amygdala (AM) atrophy in patients with TLE without foreign tissue lesion.

METHODS

We studied 65 patients with refractory TLE. They were divided into five groups according to MRIvol results: pure AM atrophy (n = 11, 10 unilateral and one bilateral), unilateral HF atrophy (n = 16), bilateral HF atrophy (n = 12), unilateral AM + HF atrophy (n = 13), and patients with normal volumes of AM and HF (n = 13). MRIvol of AM and HF were performed by using a protocol previously described by Watson et al. (Neurology 1992;42:1743-50).

RESULTS

Patients with AM atrophy had later onset of seizures compared with those with unilateral HF atrophy (p < 0.01). History of febrile convulsions (p < 0.0001) and frequent secondarily generalized tonic-clonic seizures (GTCSs) were more often found in patients with HF atrophy compared with those with pure AM atrophy and those with normal volumes (p = 0.04). Prolonged postictal confusion was more often found with AM atrophy (p = 0.05). Memory impairment was more severe in patients with HF atrophy than in those with AM atrophy only or in those with normal volumes (p = 0.03). There were no significant differences among the five groups in the following parameters: age, duration of epilepsy, seizure frequency, and presence and type of aura.

CONCLUSIONS

Prolonged postictal confusion appeared to be related to AM atrophy, in keeping with previous clinical observations. These patients also had a lower incidence of early febrile convulsions, older age at epilepsy onset, lower frequency of secondary GTCS, and lesser memory dysfunction compared with patients with hippocampal atrophy.