Prognostic Factors in Neocortical Epilepsy Surgery: Multivariate Analysis

Long-term seizure outcome in 211 patients with focal cortical dysplasia

OBJECTIVE

Focal cortical dysplasia (FCD) is currently recognized as the most common cause of neocortical pharmacoresistant epilepsy. Epilepsy surgery has become an increasingly successful treatment option. Herein, the largest patient cohort reported to date is analyzed regarding long-term outcome and factors relevant for long-term seizure control.

METHODS

Two hundred eleven children and adults undergoing epilepsy surgery for histologically proven FCD and a follow-up period of 2-12 years were analyzed regarding the longitudinal course of seizure control, effects of FCD type, localization, magnetic resonance imaging (MRI), timing of surgery, and postoperative antiepileptic treatment.

RESULTS

After 1 year, Engel class I outcome was achieved in 65% of patients and the percentage of seizure-free patients remained stable over the following (up to 12) years. Complete resection of the assumed epileptogenic area, lower age at surgery, and unilobar localization were positive prognostic indicators of long-term seizure freedom. Seizure recurrence was 12% after the first year, whereas 8% achieved late seizure freedom either following additional introduction of antiepileptic drugs (AEDs) (4%), a reoperation (2%), or a running down phenomenon (2%). Thirty-nine percent of patients had a reduction of AED from polytherapy to monotherapy or a complete cessation of AED treatment. Late seizure relapse was seen in nine patients during reduction of AEDs (i.e., in 12% of all patients with AED tapering); in four of them seizures persisted after reestablishment of antiepileptic medication.

SIGNIFICANCE

Postoperative long-term seizure outcome was favorable in patients with FCD and remained stable in 80% of patients after the first postoperative year. Several preoperative factors revealed to be predictive for the postoperative outcome and may help in the preoperative counseling of patients with FCD and in the selection of ideal candidates for epilepsy surgery.

Epilepsy surgery failure in children: a quantitative and qualitative analysis

OBJECT

Resection is a safe and effective treatment option for children with pharmacoresistant focal epilepsy, but some patients continue experience seizures after surgery. While most studies of pediatric epilepsy surgery focus on predictors of postoperative seizure outcome, these factors are often not modifiable, and the reasons for surgical failure may remain unclear.

METHODS

The authors performed a retrospective cohort study of children and adolescents who received focal resective surgery for pharmacoresistant epilepsy. Both quantitative and qualitative analyses of factors associated with persistent postoperative seizures were conducted.

RESULTS

Records were reviewed from 110 patients, ranging in age from 6 months to 19 years at the time of surgery, who underwent a total of 115 resections. At a mean 3.1-year follow-up, 76% of patients were free of disabling seizures (Engel Class I outcome). Seizure freedom was predicted by temporal lobe surgery compared with extratemporal resection, tumor or mesial temporal sclerosis compared with cortical dysplasia or other pathologies, and by a lower preoperative seizure frequency. Factors associated with persistent seizures (Engel Class II-IV outcome) included residual epileptogenic tissue adjacent to the resection cavity (40%), an additional epileptogenic zone distant from the resection cavity (32%), and the presence of a hemispheric epilepsy syndrome (28%).

CONCLUSIONS

While seizure outcomes in pediatric epilepsy surgery may be improved by the use of high-resolution neuroimaging and invasive electrographic studies, a more aggressive resection should be considered in certain patients, including hemispherectomy if a hemispheric epilepsy syndrome is suspected. Family counseling regarding treatment expectations is critical, and reoperation may be warranted in select cases.

Factors contributing to the yield of asymmetric bilateral implantation of intracranial electrodes

OBJECTIVE

To determine the outcome of implanting fewer electrodes over the hemisphere with less supporting presurgical localizing data.

METHODS

We retrospectively reviewed our epilepsy surgery database at Mayo Clinic, Rochester, Minnesota, between January 1, 1999, and December 31, 2011, to identify patients who had an asymmetric number of electrode contacts implanted in each hemisphere for seizure localization. We scored each presurgical noninvasive data point (0, 0.5, or 1) to predict the likelihood of identifying seizure onset in the hemisphere with fewer intracranial electrode contacts (HFEC). An aggregate score was obtained for each patient.

RESULTS

Thirteen (37%) of 35 patients had HFEC-onset seizures on intracranial electroencephalography (iEEG). The following factors predicted HFEC-onset seizures: (1) temporal lobe epilepsy (p = 0.02); (2) interictal scalp electroencephalographic discharges at the HFEC (p = 0.04); and (3) both interictal and ictal scalp EEG discharges at the HFEC (p = 0.01). The median (range) aggregate score was 2 (1-3) for patients with HFEC-onset seizures recorded on iEEG and 1 (0-3) for patients without HFEC-onset seizures (p = 0.001). Using this scoring model, the odds ratio of identifying HFEC-onset seizures on iEEG was 6.4 for each one-point increment in the aggregate score. The area under the receiver operating characteristic curve for this model was 0.84, suggesting excellent ability of the aggregate score to discriminate between patients with and without HFEC-onset seizures on iEEG.

SIGNIFICANCE

Implanting electrodes on the basis of limited supporting presurgical data may be useful in selected patients, especially those with temporal lobe epilepsy, interictal scalp discharges involving the HFEC, or both interictal and ictal scalp discharges involving the HFEC. In addition, our proposed scoring system may be helpful in selecting patients with complicated epilepsy for implantation of an asymmetric number of intracranial electrodes in the hemispheres.

Usefulness of interictal spike source localization in temporal lobe epilepsy: electrocorticographic study

The success of epilepsy surgery depends on delineation of the suspected epileptogenic zone. The gold standard to delineate it is to use the ictal onset zone from an electrocorticography (ECoG). Although interictal spikes are also associated with the epileptogenic zone, their clinical significance has been under-evaluated. The aim of this study was to evaluate the source localization of interictal spikes in terms of the association with epileptogenic zone in surgical temporal lobe epilepsy patients. The proposition is that the resection volume in patients with favorable outcomes includes the epileptogenic zone. The association with the epileptogenic zone was assessed as follows: (1) how many of the interictal spike sources are within the resection volume in patients with favorable outcomes and (2) how many of the interictal spike sources are outside the resection volume in patients with unfavorable outcomes. Thirty-eight temporal lobe epilepsy (TLE) patients who underwent both ECoG monitoring and epilepsy surgery were recruited and their 10min of ECoG recordings were analyzed. Six tumor-related TLE patients were excluded in the analysis. Of the remaining 32 patients, 20 patients achieved favorable surgical outcomes (Engel I and II), while the surgical outcomes of 12 patients were unfavorable (Engel III and IV). In each patient, interictal spike sources were localized using sLORETA and co-registered into a reconstructed brain model. The correspondence rate with the resection volume was estimated by counting the percentage of interictal spike sources in the resection volume. The correspondence rate in patients with favorable outcomes was 72.8±22.1, which was significantly higher than that (41.2±28.8) of the patients with unfavorable outcomes (p=0.002). Nine out of twelve patients (75%) with unfavorable outcomes had multiple interictal spike source clusters both interior and exterior to the resection volume, while 4 of the 20 patients with favorable outcomes (20%) had such multiple clusters (p=0.021). In conclusion, interictal spike sources are highly associated with the epileptogenic zone. ECoG interictal spike source localization could help in the delineation of the potential resection volume.

Focal cortical dysplasia and epilepsy surgery

Focal cortical dysplasia (FCD) is the most commonly encountered developmental malformation that causes refractory epilepsy. With advances in neuroimaging techniques, in particular MRI, recent studies have revealed a higher prevalence of FCD than previously estimated and have improved the preoperative identification and classification of these abnormalities. However, MRI frequently does not show any abnormalities in patients with pathologically proven FCD. In this situation, functional neuroimaing such as FDG-PET and ictal SPECT can be helpful. FCD is thought to be intrinsically epileptogenic, because the dysplastic tissues contain aberrant neural networks that are highly susceptible to abnormal excitation. The response to the medical treatment of epilepsy has been documented as consistently poor. Therefore, surgical resection has been an important alternative treatment for patients with intractable epilepsy related to FCD. Incomplete resection of FCD has been consistently known to be a poor prognostic factor. However, the complete removal of FCD is often difficult because the demarcation of the lesion is frequently poor, and dysplastic tissues tend to be more extensive than is apparent on MRI. Evidence indicates that even patients with MRI abnormalities who have resective epilepsy surgery for FCD have worse surgical outcomes than those of patients who have surgery for other focal lesional epilepsy syndromes. Careful planning of evelauation using intracranial electrodes is necessary for successful epilepsy surgery.

Current management and surgical outcomes of medically intractable epilepsy

Epilepsy is one of the most common neurologic disorders in the world. While anti-epileptic drugs (AEDs) are the mainstay of treatment in most cases, as many as one-third of patients will have a refractory form of disease indicating the need for a neurosurgical evaluation. Ever since the first half of the twentieth century, surgery has been a major treatment option for epilepsy, but the last 10-15 years in particular has seen several major advances. As shown in relatively recent studies, resection is more effective for medically intractable epilepsy (MIE) than AED treatment alone, which is why most clinicians now endorse a neurosurgical consultation after approximately two failed regimens of AEDs, ultimately leading to decreased healthcare costs and increased quality of life. Temporal lobe epilepsy (TLE) is the most common form of MIE and comprises about 80% of epilepsy surgeries with the majority of patients gaining complete seizure-freedom. As the number of procedures and different approaches continues to grow, temporal lobectomy remains consistently focused on resection of mesial structures such as the amygdala, hippocampus, and parahippocampal gyrus while preserving as much of the neocortex as possible resulting in optimum seizure control with minimal neurological deficits. MIE originating outside the temporal lobe is also effectively treated with resection. Though not as successful as TLE surgery because of their frequent proximity to eloquent brain structures and more diffuse pathology, epileptogenic foci located extratemporally also benefit from resection. Favorable seizure outcome in each of these procedures has heavily relied on pre-operative imaging, especially since the massive surge in MRI technology just over 20 years ago. However, in the absence of visible lesions on MRI, recent improvements in secondary imaging modalities such as fluorodeoxyglucose positron emission computed tomography (FDG-PET) and single-photon emission computed tomography (SPECT) have lead to progressively better long-term seizure outcomes by increasing the neurosurgeon's visualization of supposed non-lesional foci. Additionally, being historically viewed as a drastic surgical intervention for MIE, hemispherectomy has been extensively used quite successfully for diffuse epilepsies often found in pediatric patients. Although total anatomic hemispherectomy is not utilized as commonly today, it has given rise to current disconnective techniques such as hemispherotomy. Therefore, severe forms of hemispheric developmental epilepsy can now be surgically treated while substantially decreasing the amount of potential long-term complications resulting from cavitation of the brain following anatomical hemispherectomy. Despite the rapid pace at which we are gaining further knowledge about epilepsy and its surgical treatment, there remains a sizeable underutilization of such procedures. By reviewing the recent literature on resective treatment of MIE, we provide a recent up-date on epilepsy surgery while focusing on historical perspectives, techniques, prognostic indicators, outcomes, and complications associated with several different types of procedures.

Surgical Outcomes in Patients With Extratemporal Epilepsy and Subtle or Normal Magnetic Resonance Imaging Findings

BACKGROUND:

Surgery is an important therapeutic option in patients with medically refractory epilepsy. The combination of an extratemporal epileptic focus and nonlesional magnetic resonance imaging (MRI) was often believed to portend a poor outcome.

OBJECTIVE:

To investigate the outcome and analyze potential prognostic predictors in patients without lesions on MRI who underwent extratemporal resections.

METHODS:

Clinical, presurgical evaluation, invasive monitoring, and postoperative data of patients with high-resolution MRI that was initially reported as nonlesional were reviewed. Patients were reclassified as MRI-positive if an MRI abnormality related to the epilepsy was revealed at the multidisciplinary presurgical patient management conference, or as MRI-negative if imaging remained normal or revealed incidental findings.

RESULTS:

Sixty patients were identified; 72% were MRI-negative. In the original cohort, the median seizure-free duration was 1.32 years (95% confidence interval [CI], 0.16-2.0); probability of seizure freedom at 2 years was 36% (95% CI, 30%–43%). In the MRI-negative group, the median seizure-free duration was 1.52 years (95% CI, 0.12-5.17); probability of seizure freedom at 2 years was 42% (95% CI, 33%–50%). Complete resection of ictal onset areas and absence of acute postoperative seizures were significantly associated with longer seizure freedom (risk ratio 4.9, P = .004; 95% CI, 1.6-16.7 and 22.1, P < .001; 95% CI, 5.9-94.7, respectively).

CONCLUSION:

Among patients with medically refractory MRI nonlesional extratemporal epilepsy, detailed evaluation and subsequent resection leads to seizure freedom in 42% of patients at 2 years.

Computer-Aided Diagnosis and Localization of Lateralized Temporal Lobe Epilepsy Using Interictal FDG-PET

Interictal FDG-PET (iPET) is a core tool for localizing the epileptogenic focus, potentially before structural MRI, that does not require rare and transient epileptiform discharges or seizures on EEG. The visual interpretation of iPET is challenging and requires years of epilepsy-specific expertise. We have developed an automated computer-aided diagnostic (CAD) tool that has the potential to work both independent of and synergistically with expert analysis. Our tool operates on distributed metabolic changes across the whole brain measured by iPET to both diagnose and lateralize temporal lobe epilepsy (TLE). When diagnosing left TLE (LTLE) or right TLE (RTLE) vs. non-epileptic seizures (NES), our accuracy in reproducing the results of the gold standard long term video-EEG monitoring was 82% [95% confidence interval (CI) 69-90%] or 88% (95% CI 76-94%), respectively. The classifier that both diagnosed and lateralized the disease had overall accuracy of 76% (95% CI 66-84%), where 89% (95% CI 77-96%) of patients correctly identified with epilepsy were correctly lateralized. When identifying LTLE, our CAD tool utilized metabolic changes across the entire brain. By contrast, only temporal regions and the right frontal lobe cortex, were needed to identify RTLE accurately, a finding consistent with clinical observations and indicative of a potential pathophysiological difference between RTLE and LTLE. The goal of CADs is to complement - not replace - expert analysis. In our dataset, the accuracy of manual analysis (MA) of iPET (∼80%) was similar to CAD. The square correlation between our CAD tool and MA, however, was only 30%, indicating that our CAD tool does not recreate MA. The addition of clinical information to our CAD, however, did not substantively change performance. These results suggest that automated analysis might provide clinically valuable information to focus treatment more effectively.

Do neuroimaging results impact prognosis of epilepsy surgery? A meta-analysis

The neuroimaging results of drug-resistant epilepsy patients play an important role in the surgery decision and prognosis. The aim of this study was to evaluate the impact of these results on the efficacy of epilepay surgery, and then to explore surgical benefit for epilepsy patients with negative magnetic resonance (MR) images. Twenty-four subgroups describing the outcomes of 1475 epilepsy patients with positive-neuroimaging results and 696 patients with negative-neuroimaging results were involved in the meta-analysis. Overall, the odds of postoperational seizure-free rate were 2.03 times higher in magnetic resonance imaging-positive (MRI-positive) patients than in MRI-negative patients [odds ratio (OR)=2.03, 95% CI (1.67, 2.47), P<0.00001]. For patients with temporal lobe epilepsy (TLE), the odds were 1.76 times higher in those with MRI-positive results than in those with MRI-negative results [OR=1.76, 95% CI (1.34, 2.32), P<0.0001]. For patients with extra-temporal lobe epilepsy (extra-TLE), the odds were 2.88 times higher in MRI-positive patients than in MRI-negative patients [OR=2.88, 95% CI (1.53, 5.43), P=0.001]. It was concluded that the seizure-free rate of MRI-positive patients after surgery was higher than that of MRI-negative patients. For patients with negative results, an appropriate surgery should be concerned for TLE.

Magnetoencephalography interictal spike clustering in relation with surgical outcome of cortical dysplasia

OBJECTIVE

The aim of this study was to devise an objective clustering method for magnetoencephalography (MEG) interictal spike sources, and to identify the prognostic value of the new clustering method in adult epilepsy patients with cortical dysplasia (CD).

METHODS

We retrospectively analyzed 25 adult patients with histologically proven CD, who underwent MEG examination and surgical resection for intractable epilepsy. The mean postoperative follow-up period was 3.1 years. A hierarchical clustering method was adopted for MEG interictal spike source clustering. Clustered sources were then tested for their prognostic value toward surgical outcome.

RESULTS

Postoperative seizure outcome was Engel class I in 6 (24%), class II in 3 (12%), class III in 12 (48%), and class IV in 4 (16%) patients. With respect to MEG spike clustering, 12 of 25 (48%) patients showed 1 cluster, 2 (8%) showed 2 or more clusters within the same lobe, 10 (40%) showed 2 or more clusters in a different lobe, and 1 (4%) patient had only scattered spikes with no clustering. Patients who showed focal clustering achieved better surgical outcome than distributed cases (p=0.017).

CONCLUSION

This is the first study that introduces an objective method to classify the distribution of MEG interictal spike sources. By using a hierarchical clustering method, we found that the presence of focal clustered spikes predicts a better postoperative outcome in epilepsy patients with CD.

Localization value of magnetoencephalography interictal spikes in adult nonlesional neocortical epilepsy

Few studies have included magnetoencephalography (MEG) when assessing the diagnostic value of presurgical modalities in a nonlesional epilepsy population. Here, we compare single photon emission computed tomography (SPECT), positron emission tomography (PET), video-EEG (VEEG), and MEG, with intracranial EEG (iEEG) to determine the value of individual modalities to surgical decisions. We analyzed 23 adult epilepsy patients with no abnormal MRI findings who had undergone surgical resection. Localization of individual presurgical tests was determined for hemispheric and lobar locations based on visual analysis. Each localization result was compared with the ictal onset zone (IOZ) defined by using iEEG. The highest to the lowest hemispheric concordance rates were MEG (83%) > ictal VEEG (78%) > PET (70%) > ictal SPECT (57%). The highest to lowest lobar concordance rates were ictal VEEG = MEG (65%) > PET (57%) > ictal SPECT (52%). Statistical analysis showed MEG to have a higher hemispheric concordance than that of ictal SPECT (P = 0.031). We analyzed the effects of MEG clustered-area resection on surgical outcome. Patients who had resection of MEG clusters showed a better surgical outcome than those without such resection (P = 0.038). It is suggested that MEG-based localization had the highest concordance with the iEEG-defined IOZ. Furthermore, MEG cluster resection has prognostic significance in predicting surgical outcome.

Advances in the diagnosis and treatment of epilepsy

Epilepsy is the most common serious brain disorder in children, occurring in all parts of the world and within every stratum of the population. Through its effects, it exerts a significant physical, psychological, economic, and social toll on children and their caregivers. Historically, the surgical treatment of epilepsy has been viewed with skepticism with regard to its indications, safety, and therapeutic benefit. However, continued refinements in diagnostic and operative techniques are helping to put to rest the antiquated notion that surgery is a last-resort procedure in the management of pediatric epilepsy. Surgery can be performed safely, even in infants and young children, with excellent patient outcomes in properly selected patients. This review focuses on the surgical treatment of pediatric epilepsy. A brief background discussion of seizures and epilepsy is followed by a substantive discussion regarding the intricacies of selecting patients for epilepsy surgery, emphasizing the important role of advanced imaging techniques in the decision-making process. The indications and outcomes of the most common epilepsy surgical procedures are then reviewed. The article ends with a discussion of the future of epilepsy surgery.

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.

Rates and predictors of long-term seizure freedom after frontal lobe epilepsy surgery: a systematic review and meta-analysis

OBJECT

Frontal lobe epilepsy (FLE) is the second-most common focal epilepsy syndrome, and seizures are medically refractory in many patients. Although various studies have examined rates and predictors of seizure freedom after resection for FLE, there is significant variability in their results due to patient diversity, and inadequate follow-up may lead to an overestimation of long-term seizure freedom.

METHODS

In this paper the authors report a systematic review and meta-analysis of long-term seizure outcomes and predictors of response after resection for intractable FLE. Only studies of at least 10 patients examining seizure freedom after FLE surgery with postoperative follow-up duration of at least 48 months were included.

RESULTS

Across 1199 patients in 21 studies, the overall rate of postoperative seizure freedom (Engel Class I outcome) was 45.1%. No trend in seizure outcomes across all studies was observed over time. Significant predictors of long-term seizure freedom included lesional epilepsy origin (relative risk [RR] 1.67, 95% CI 1.36-28.6), abnormal preoperative MRI (RR 1.64, 95% CI 1.32-2.08), and localized frontal resection versus more extensive lobectomy with or without an extrafrontal component (RR 1.71, 95% CI 1.26-2.43). Within lesional FLE cases, gross-total resection led to significantly improved outcome versus subtotal lesionectomy (RR 1.99, 95% CI 1.47-2.84).

CONCLUSIONS

These findings suggest that FLE patients with a focal and identifiable lesion are more likely to achieve seizure freedom than those with a more poorly defined epileptic focus. While seizure freedom can be achieved in the surgical treatment of medically refractory FLE, these findings illustrate the compelling need for improved noninvasive and invasive localization techniques in FLE.

Long-term outcome in children with intractable epilepsy showing bilateral diffuse cortical glucose hypometabolism pattern on positron emission tomography

The objective of this study is to determine the long-term outcome of children with intractable epilepsy who have diffuse cortical hypometabolism on 2-deoxy-2-((18)F)fluoro-D-glucose positron emission tomography (FDG-PET) scans. Seventeen children with intractable epilepsy showing bilateral, diffuse cortical hypometabolism on FDG-PET were followed up through telephone interview from 1 year 4 months to 11 years 4 months (mean: 5 years 7 months ± 2 years 1 month) after their PET scans. One child succumbed to Sanfilippo disease at age 20 years. Only 2 children were seizure free. Fifty percent had walking difficulties, 56.25% were not toilet trained, all had speech difficulties, 43.75% had behavioral problems, 37.5% had poor eye contact, 75% had socialization difficulties, and 87.5% attended special schools. Three children were found to have genetic causes, including a 4-MB deletion of the mitochondrial genome, MECP2 duplication, and Lafora disease. In conclusion, the long-term outcome in this patient population is poor, and they tend to suffer from genetic/neurodegenerative diseases.

Surgical approaches in nonlesional neocortical epilepsy

There is inherent difficulty in identifying the epileptogenic zone in nonlesional neocortical epilepsy, which leads to the incomplete resection. However, with careful interpretation of other studies including functional neuroimaging and the presence of concordant results, surgical treatment can benefit selected patients with nonlesional neocortical epilepsy. Two recent large studies including ours demonstrated that seizure free outcomes were 47 and 55% for nonlesional TLE, and 41 and 43% for nonlesional extratemporal lobe epilepsy patients. Concordance with two or more presurgical evaluations among interictal EEG, ictal EEG, FDG-PET, and ictal SPECT was significantly related to a seizure-free outcome. However, we should be cautious to the possibility of false localization of ictal EEG or functional neuroimaging in nonlesional neocortical epilepsy. Careful placement of intracranial electrodes on the presumed epileptogenic zone and the adjacent areas should be needed for these patients. The repositioning of intracranial electrodes after the failure in identifying ictal onset zone at the initial intracranial study might identify a new ictal onset zone. Consideration of one-week interval repositioning of intracranial electrodes could be helpful in selected patients. Intracranial EEG is one of the most important procedures in planning surgery and achieving a good surgical outcome in resective epilepsy surgery. Slow propagation and focal or regional ictal onset rather than widespread onset were associated with a seizure-free outcome. Complete resection including the area with initial three second ictal rhythm and interictal abnormalities predicts a good surgical outcome.

Independent predictors and a prognostic model for surgical outcome in refractory frontal lobe epilepsy

PURPOSE

Refractory frontal lobe epilepsy (FLE) remains one of the most challenging surgically remediable epilepsy syndromes. Nevertheless, definition of independent predictors and predictive models of postsurgical seizure outcome remains poorly explored in FLE.

METHODS

We retrospectively analyzed data from 70 consecutive patients with refractory FLE submitted to surgical treatment at our center from July 1994 to December 2006. Univariate results were submitted to logistic regression models and Cox proportional hazards regression to identify isolated risk factors for poor surgical results and to construct predictive models for surgical outcome in FLE.

RESULTS

From 70 patients submitted to surgery, 45 patients (64%) had favorable outcome and 37 (47%) became seizure free. Isolated risk factors for poor surgical outcome are expressed in hazard ratio (H.R.) and were time of epilepsy (H.R.=4.2; 95% C.I.=1.5-11.7; p=0.006), ictal EEG recruiting rhythm (H.R.=2.9; 95% C.I.=1.1-7.7; p=0.033); normal MRI (H.R.=4.8; 95% C.I.=1.4-16.6; p=0.012), and MRI with lesion involving eloquent cortex (H.R.=3.8; 95% C.I.=1.2-12.0; p=0.021). Based on these variables and using a logistic regression model we constructed a model that correctly predicted long-term surgical outcome in up to 80% of patients.

CONCLUSION

Among independent risk factors for postsurgical seizure outcome, epilepsy duration is a potentially modifiable factor that could impact surgical outcome in FLE. Early diagnosis, presence of an MRI lesion not involving eloquent cortex, and ictal EEG without recruited rhythm independently predicted favorable outcome in this series.

Epilepsy surgery in Argentina: long-term results in a comprehensive epilepsy centre

RATIONALE

Epilepsy surgery procedures started in Argentina more than 50 years ago. This is the first comprehensive and systematic survey of epilepsy surgery long-term outcome from our country.

METHODS

A descriptive cohort study was conducted between 1998 and 2008 for drug-resistant epilepsy surgery with a minimum of 12 months follow-up (n=110). In 84 cases (76.36%) resective surgery was performed, and outcome periodically assessed using the Engel score. Patients were stratified into groups: 12, 13-36, 37-60 and over than 60 months of follow-up. Video-EEG with and without intracranial electrode implants, intraoperative electrocorticograms, Wada tests, pathology reports, use of antiepileptic drugs (AEDs), and surgical complication rates were evaluated.

RESULTS

Surgical techniques included: 69 lobectomies (62.7%), 15 lesionectomies (13.6%), 6 callosotomies (5.4%), 6 multiple subpial transection (5.4%), 11 vagus nerve stimulations (10%), 3 hemispherectomies (2.7%). Male: female ratio: 1/1.44. Mean age at time of surgery: 26.2 years. Mean duration of epilepsy: 14 years. Age at seizure onset: 11.5 years. Mean follow-up: 46 months. Pathology findings: mesial temporal sclerosis 32 (35.1%); dual pathology 17 (18.7%); cortical dysplasia 15 (16.4%); non-specific inflammatory changes 11 (12.1%); tumors 7 (7.7%); other 6 (6.8%). Engel scores at 12 months follow-up: 72.6% (61) class I, 16.6% (14) class II and 15.5% (13) class III-IV; 13-36 months after surgery: 68.1% of cases were class I, 15.9% class II and 15.5% class III-IV. After 37-60 months, 74% class I, 14% class II, 14% class III-IV. Over 60 months (n=45) 78% class I, 13.5% class II and 8.1% class III-IV.

CONCLUSION

Conducting a successful epilepsy surgery program in a developing country is challenging. These results should encourage specialists in these countries. Long-term outcome results comparable to centres in developed countries can be achieved.

Presurgical epilepsy localization with interictal cerebral dysfunction

Localization of interictal cerebral dysfunction with 2-[(18)F]fluoro-2-D-deoxyglucose (FDG) positron emission tomography (PET) and neuropsychological examination usefully supplements electroencephalography (EEG) and brain magnetic resonance imaging (MRI) in planning epilepsy surgery. In MRI-negative mesial temporal lobe epilepsy, correlation of temporal lobe hypometabolism with extracranial ictal EEG can support resection without prior intracranial EEG monitoring. In refractory localization-related epilepsies, hypometabolic sites may supplement other data in hypothesizing likely ictal onset zones in order to intracranial electrodes for ictal recording. Prognostication of postoperative seizure freedom with FDG PET appears to have greater positive than negative predictive value. Neuropsychological evaluation is critical to evaluating the potential benefit of epilepsy surgery. Cortical deficits measured with neuropsychometry are limited in lateralizing and localizing value for determination of ictal onset sites, however. Left temporal resection risks iatrogenic verbal memory deficits and dysnomia, and neuropsychological findings are useful in predicting those at greatest risk. Prognostication of cognitive risks with resection at other sites is less satisfactory.

Is it necessary to define the ictal onset zone with EEG prior to performing resective epilepsy surgery?

When evaluating candidates for neurosurgical treatment for medically intractable epilepsy, is it always necessary to define the region of seizure onset with EEG? A simple answer to this question is not possible. There are specific situations where surgery is commonly performed without clear EEG ictal localization, and other situations where electrical localization is mandatory. However, opinions differ in many other situations. What are the core issues for determining when EEG localization is necessary? Neuroimaging is imperfect. It does not always accurately identify the site of seizure origination, because seizures do not always arise from visible structural lesions. EEG localization is also imperfect, as well as expensive and time consuming. Sometimes the site of origin is not identified, or a region of spread is misidentified as site of origin. False localization and lateralization can occur. Finally, epilepsy surgery is imperfect. It can produce life-changing results, but it carries risk, and surgical failure is not rare. The limitations of these methods, and the high stakes of epilepsy surgery imply that we should be very cautious to omit EEG studies. The desire to improve access to epilepsy surgery, and to minimize the expense and risk from inpatient EEG studies, must be weighed against the possibility of an ineffective resection. To improve outcomes, improvements in both neuroimaging and EEG techniques are needed.

Acute postoperative seizures after epilepsy surgery - a long-term outcome predictor?

OBJECTIVES

The prognostic value of acute postoperative seizures (APS) after epilepsy surgery is much debated. This study evaluated APS, defined as seizures in the first week post-surgery, as a predictor of long-term seizure outcome, and investigated the utility of other potential outcome predictors.

MATERIALS AND METHODS

Medical records of 48 patients with temporal and extra-temporal epilepsy surgery were studied. Forty patients had lesional surgery. All had at least 2 year postoperative follow-up.

RESULTS

At 2 year follow-up, 25 patients (53%) were seizure free. Univariate analysis showed that APS (P = 0.048), using ≥ six AEDs prior to surgery (P = 0.03), pathological postoperative EEG (P = 0.043) and female gender (P = 0.012) were associated with seizure recurrence.

CONCLUSIONS

Univariate analysis indicate that APS, a high number of AEDs used prior to surgery, and pathological postoperative EEG are possible predictors of seizure recurrence after epilepsy surgery. Only gender retained significance in the multivariate analysis.

Longitudinal Change in Outcome of Frontal Lobe Epilepsy Surgery

BACKGROUND:

Although the outcome of epilepsy surgery changes with time, few studies have considered longitudinal changes after frontal lobe epilepsy (FLE) surgery.

OBJECTIVE:

To assess the longitudinal changes after FLE surgery.

METHODS:

Resection of the seizure onset zone was performed in 76 patients with FLE. Invasive monitoring was performed in 56 of these 76. Awake craniotomy was performed in 43 of the 76 patients. More than 50% of patients were followed up for at least 7 years. The mean follow-up was 81 months.

RESULTS:

For all patients, the seizure-free rate was 79% at 6 months, 64% at 1 year, 55% at 2 years, and 55% at 7 years. For patients with cortical dysplasia, the seizure-free rate was 72% at 6 months, 53% at 1 year, 51% at 2 years, and 46% at 7 years. For patients with tumor, the seizure-free rate was 89% at 6 months, 83% at 1 year, 83% at 2 years, and 74% at 7 years. Patients with tumor showed better outcome than those with cortical dysplasia (P = .04). Although the overall seizure-free rate became stable after 2 years, individual status changed for up to 5 years. Seizures recurred in 11 patients within 1 year (early recurrence) and in 12 patients by 1 to 5 years (late recurrence). Antiepileptic drug (AED) medication was adjusted in all patients with recurrence. Patients with late recurrence had a more favorable response (Engel class I or II) than early recurrence (P &lt; .01).

CONCLUSION:

The overall seizure outcome changes mostly during the first year. However, individual seizure status changes for up to 5 years. The outcome of late recurrence is favorable to AED adjustment.

Diagnostic methods for extra-temporal neocortical focal epilepsies: present and future

The progress of epilepsies diagnosis has been great, but, amongst the diagnostic detailing that demand research, one of the most important is the essential lateralization and localization of epileptogenic zone, considered as the cerebral cortex region, that removed, will result in a free state of seizures. The present study aims to analyze the possible uses of proton spectroscopy for clinical and pre-surgical evaluation of focal extratemporal epilepsies, since this group presents the highest difficulty degree for lateralizing and locating epileptogenic zones. In almost all cases, a non invasive diagnosis can be performed using routine electroencephalography, video-electroencephalography - considered as gold standard, and magnetic resonance imaging. However, when the results of these exams are contradictory, some patients need invasive techniques, as the intra-cranial video-EEG, using deep electrodes, sub-dural strip and grid, that are associated with increased diagnostic cost and risk of complications, as cerebral hemorrhages and intra-cranial infections. Proton spectroscopy appears as a possibility, given its capacity to evaluate cerebral metabolism, by N-acetyl-aspartate (NAA), creatine (Cre) and choline (Cho) concentrations, amongst other metabolites. This non invasive method may provide time reduction of this evaluation and reliable level improvement for this topographical diagnosis.

Multimodal neuroimaging in presurgical evaluation of childhood epilepsy

In pre-surgical evaluation of pediatric epilepsy, the combined use of multiple imaging modalities for precise localization of the epileptogenic focus is a worthwhile endeavor. Advanced neuroimaging by high field Magnetic resonance imaging (MRI), diffusion tensor images, and MR spectroscopy have the potential to identify subtle lesions. ¹⁸F-FDG positron emission tomography and single photon emission tomography provide visualization of metabolic alterations of the brain in the ictal and interictal states. These techniques may have localizing value for patients which exhibit normal MRI scans. Functional MRI is helpful for non-invasively identifying areas of eloquent cortex. These advances are improving our ability to noninvasively detect epileptogenic foci which have gone undetected in the past and whose accurate localization is crucial for a favorable outcome following surgical resection.

Extent of neocortical resection and surgical outcome of epilepsy: intracranial EEG analysis

PURPOSE

Intracranial electroencephalography (EEG) monitoring is an important process in the presurgical evaluation for epilepsy surgery. The objective of this study was to identify the ideal resection margin in neocortical epilepsy guided by subdural electrodes. For this purpose, we investigated the relationship between the extent of resection guided by subdural electrodes and the outcome of epilepsy surgery.

METHODS

Intracranial EEG studies were analyzed in 177 consecutive patients who had undergone resective epilepsy surgery. We reviewed various intracranial EEG findings and resection extent. We analyzed the relationships between the surgical outcomes and intracranial EEG factors: the frequency, morphology, and distribution of ictal-onset discharges, the propagation speed, and the time lag between clinical and intracranial ictal onset. We also investigated whether the extent of resection, including the area showing ictal rhythm and various interictal abnormalities--such as frequent interictal spikes, pathologic delta waves, and paroxysmal fast activity--influenced the surgical outcome.

RESULTS

Seventy-five patients (42%) were seizure free. A seizure-free outcome was significantly associated with a resection that included the area showing ictal spreading rhythm during the first 3 s or included all the electrodes showing pathologic delta waves or frequent interictal spikes. However, subgroup analysis revealed that the extent of resection did not affect the surgical outcome in lateral temporal lobe epilepsy.

CONCLUSIONS

The extent of resection is closely associated with surgical outcome, especially in extratemporal lobe epilepsy. Resection that includes the area with total pathologic delta waves and frequent interictal spikes predicts a good surgical outcome.

Anatomy-based reconstruction of FDG-PET images with implicit partial volume correction improves detection of hypometabolic regions in patients with epilepsy due to focal cortical dysplasia diagnosed on MRI

PURPOSE

Detection of hypometabolic areas on interictal FDG-PET images for assessing the epileptogenic zone is hampered by partial volume effects. We evaluated the performance of an anatomy-based maximum a-posteriori (A-MAP) reconstruction algorithm which combined noise suppression with correction for the partial volume effect in the detection of hypometabolic areas in patients with focal cortical dysplasia (FCD).

METHODS

FDG-PET images from 14 patients with refractory partial epilepsy were reconstructed using A-MAP and maximum likelihood (ML) reconstruction. In all patients, presurgical evaluation showed that FCD represented the epileptic lesion. Correspondence between the FCD location and regional metabolism on a predefined atlas was evaluated. An asymmetry index of FCD to normal cortex was calculated.

RESULTS

Hypometabolism at the FCD location was detected in 9/14 patients (64%) using ML and in 10/14 patients (71%) using A-MAP reconstruction. Hypometabolic areas outside the FCD location were detected in 12/14 patients (86%) using ML and in 11/14 patients (79%) using A-MAP reconstruction. The asymmetry index was higher using A-MAP reconstruction (0.61, ML 0.49, p=0.03).

CONCLUSION

The A-MAP reconstruction algorithm improved visual detection of epileptic FCD on brain FDG-PET images compared to ML reconstruction, due to higher contrast and better delineation of the lesion. This improvement failed to reach significance in our small sample. Hypometabolism outside the lesion is often present, consistent with the observation that the functional deficit zone tends to be larger than the epileptogenic zone.

Quantitative brain surface mapping of an electrophysiologic/metabolic mismatch in human neocortical epilepsy

The spatial relationship between an intracranial EEG-defined epileptic focus and cortical hypometabolism on glucose PET has not been precisely described. In order to quantitatively evaluate the hypothesis that ictal seizure onset and/or rapid seizure propagation, detected by subdural EEG monitoring, commonly involves normometabolic cortex adjacent to hypometabolic cortical regions, we applied a novel, landmark-constrained conformal mapping approach in 14 children with refractory neocortical epilepsy. The 3D brain surface was parcellated into finite cortical elements (FCEs), and hypometabolism was defined using lobe- and side-specific asymmetry indices derived from normal adult controls. The severity and location of hypometabolic areas vs. ictal intracranial EEG abnormalities were compared on the 3D brain surface. Hypometabolism was more severe in the seizure onset zone than in cortical areas covered by non-onset electrodes. However, similar proportions of the onset electrodes were located over and adjacent to (within 2 cm) hypometabolic regions (46% vs. 41%, respectively), whereas rapid seizure spread electrodes preferred these "adjacent areas" rather than the hypometabolic area itself (51% vs. 22%). On average, 58% of the hypometabolic regions had no early seizure involvement. These findings strongly support that the seizure onset zone often extends from hypometabolic to adjacent normometabolic cortex, while large portions of hypometabolic cortex are not involved in seizure onset or early propagation. The clinical utility of FDG PET in guiding subdural electrode placement in neocortical epilepsy could be greatly enhanced by extending grid coverage to at least 2 cm beyond hypometabolic cortex, when feasible.