Association of combined MRI, interictal EEG, and ictal EEG results with outcome and pathology after temporal lobectomy

Quantitative Analysis of Visually Reviewed Normal Scalp EEG Predicts Seizure Freedom Following Anterior Temporal Lobectomy

Objective

Anterior temporal lobectomy (ATL) is a widely performed and successful intervention for drug‐resistant temporal lobe epilepsy (TLE). However, up to one third of patients experience seizure recurrence within 1 year after ATL. Despite the extensive literature on presurgical electroencephalography (EEG) and magnetic resonance imaging (MRI) abnormalities to prognosticate seizure freedom following ATL, the value of quantitative analysis of visually reviewed normal interictal EEG in such prognostication remains unclear. In this retrospective multicenter study, we investigate whether machine learning analysis of normal interictal scalp EEG studies can inform the prediction of postoperative seizure freedom outcomes in patients who have undergone ATL.

Methods

We analyzed normal presurgical scalp EEG recordings from 41 Mayo Clinic (MC) and 23 Cleveland Clinic (CC) patients. We used an unbiased automated algorithm to extract eyes closed awake epochs from scalp EEG studies that were free of any epileptiform activity and then extracted spectral EEG features representing (a) spectral power and (b) interhemispheric spectral coherence in frequencies between 1 and 25 Hz across several brain regions. We analyzed the differences between the seizure‐free and non–seizure‐free patients and employed a Naïve Bayes classifier using multiple spectral features to predict surgery outcomes. We trained the classifier using a leave‐one‐patient‐out cross‐validation scheme within the MC data set and then tested using the out‐of‐sample CC data set. Finally, we compared the predictive performance of normal scalp EEG‐derived features against MRI abnormalities.

Results

We found that several spectral power and coherence features showed significant differences correlated with surgical outcomes and that they were most pronounced in the 10–25 Hz range. The Naïve Bayes classification based on those features predicted 1‐year seizure freedom following ATL with area under the curve (AUC) values of 0.78 and 0.76 for the MC and CC data sets, respectively. Subsequent analyses revealed that (a) interhemispheric spectral coherence features in the 10–25 Hz range provided better predictability than other combinations and (b) normal scalp EEG‐derived features provided superior and potentially distinct predictive value when compared with MRI abnormalities (>10% higher F1 score).

Significance

These results support that quantitative analysis of even a normal presurgical scalp EEG may help prognosticate seizure freedom following ATL in patients with drug‐resistant TLE. Although the mechanism for this result is not known, the scalp EEG spectral and coherence properties predicting seizure freedom may represent activity arising from the neocortex or the networks responsible for temporal lobe seizure generation within vs outside the margins of an ATL.

Prognostic factors of postoperative seizure outcomes in older patients with temporal lobe epilepsy

OBJECTIVE

The authors of this study aimed to investigate surgical outcomes and prognostic factors in older patients with drug-resistant temporal lobe epilepsy (TLE) who had undergone resective surgery.

METHODS

Data on patients older than 45 years of age with drug-resistant TLE who had undergone resective surgery at Sanbo Brain Hospital, Capital Medical University, between January 2009 and August 2017 were retrospectively collected. Postoperative seizure outcomes were evaluated according to the International League Against Epilepsy (ILAE) classification. Patients belonging to ILAE classes 1 and 2 were classified as having a favorable outcome, whereas patients belonging to ILAE classes 3-6 were classified as having an unfavorable outcome. Univariate analysis and multivariate logistic regression analysis were used to identify the potential predictors of seizure outcomes.

RESULTS

A total of 45 patients older than 45 years of age who had undergone resective epilepsy surgery for TLE were included in the present study. Eight (17.8%) of 45 patients had preoperative comorbidity in addition to seizures. The average age at the time of surgery was 51.76 years, and the average duration of epilepsy at the time surgery was 18.01 years. After an average follow-up period of 4.53 ± 2.82 years (range 2-10 years), 73.3% (33/45) of patients were seizure free. Surgical complications were observed in 13.3% of patients. Univariate and multivariate analyses revealed that an MRI-negative finding is the only independent predictor of unfavorable seizure outcomes (OR 0.06, 95% CI 0.01-0.67, p = 0.023).

CONCLUSIONS

Resective surgery is a safe and effective treatment for older patients with drug-resistant TLE. An MRI-negative finding independently predicts unfavorable seizure outcomes.

The Role of Interictal Epileptiform Discharges in Epilepsy Surgery Outcome

Background:

Epilepsy surgery is a fundamental treatment in refractory epilepsy. Video electroencephalographic (v-EEG) monitoring plays an essential role in presurgical evaluation of patients. However there are reports of favorable outcome based on interictal and magnetic resonance imaging (MRI) findings without any need for v-EEG monitoring in patients with temporal lobe epilepsy (TLE). This study aimed to investigate the prognostic effect of concordance between interictal findings and ictal and MRI data on postsurgical outcome of TLE and extratemporal lobe epilepsy (ETLE).

Methods:

A retrospective study was conducted on 199 patients with refractory focal epilepsy who were admitted for presurgical evaluation. The concordance between irritative zone (IZ) and seizure onset zone (SOZ) and also IZ and MRI lesion was registered, and subsequently the prognostic effect of relevancy on 1-year follow-up result based on Engel criteria was investigated.

Results:

In TLE and ETLE regarding relevancy between IZ and SOZ, 77.8% and 73.2% were concordant, 2.5% and 0% were discordant, and 19.6% and 26.8% had overlap, respectively. Concordance between IZ and MRI lesion was found in 76.6% and 51.2% of patients with TLE and ETLE while discordance was recorded in 2.5% and 12.2% and overlap registered in 20.9% and 36.6%, respectively. The concordance of interictal findings had no effect on postsurgical outcome of patients with TLE and ETLE.

Conclusions:

Our study showed that concordance of IZ with SOZ and MRI has no independent effect on postsurgical outcome of patients with TLE and ETLE. We suggest that excluding exceptional cases, v-EEG monitoring should be considered as the mainstay of presurgical evaluation.

Surgery for epilepsy

BACKGROUND

This is an updated version of the original Cochrane review, published in 2015.Focal epilepsies are caused by a malfunction of nerve cells localised in one part of one cerebral hemisphere. In studies, estimates of the number of individuals with focal epilepsy who do not become seizure-free despite optimal drug therapy vary between at least 20% and up to 70%. If the epileptogenic zone can be located, surgical resection offers the chance of a cure with a corresponding increase in quality of life.

OBJECTIVES

The primary objective is to assess the overall outcome of epilepsy surgery according to evidence from randomised controlled trials.Secondary objectives are to assess the overall outcome of epilepsy surgery according to non-randomised evidence, and to identify the factors that correlate with remission of seizures postoperatively.

SEARCH METHODS

For the latest update, we searched the following databases on 11 March 2019: Cochrane Register of Studies (CRS Web), which includes the Cochrane Epilepsy Group Specialized Register and the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid, 1946 to March 08, 2019), ClinicalTrials.gov, and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP).

SELECTION CRITERIA

Eligible studies were randomised controlled trials (RCTs) that included at least 30 participants in a well-defined population (age, sex, seizure type/frequency, duration of epilepsy, aetiology, magnetic resonance imaging (MRI) diagnosis, surgical findings), with an MRI performed in at least 90% of cases and an expected duration of follow-up of at least one year, and reporting an outcome related to postoperative seizure control. Cohort studies or case series were included in the previous version of this review.

DATA COLLECTION AND ANALYSIS

Three groups of two review authors independently screened all references for eligibility, assessed study quality and risk of bias, and extracted data. Outcomes were proportions of participants achieving a good outcome according to the presence or absence of each prognostic factor of interest. We intended to combine data with risk ratios (RRs) and 95% confidence intervals (95% CIs).

MAIN RESULTS

We identified 182 studies with a total of 16,855 included participants investigating outcomes of surgery for epilepsy. Nine studies were RCTs (including two that randomised participants to surgery or medical treatment (99 participants included in the two trials received medical treatment)). Risk of bias in these RCTs was unclear or high. Most of the remaining 173 non-randomised studies followed a retrospective design. We assessed study quality using the Effective Public Health Practice Project (EPHPP) tool and determined that most studies provided moderate or weak evidence. For 29 studies reporting multivariate analyses, we used the Quality in Prognostic Studies (QUIPS) tool and determined that very few studies were at low risk of bias across domains.In terms of freedom from seizures, two RCTs found surgery (n = 97) to be superior to medical treatment (n = 99); four found no statistically significant differences between anterior temporal lobectomy (ATL) with or without corpus callosotomy (n = 60), between subtemporal or transsylvian approach to selective amygdalohippocampectomy (SAH) (n = 47); between ATL, SAH and parahippocampectomy (n = 43) or between 2.5 cm and 3.5 cm ATL resection (n = 207). One RCT found total hippocampectomy to be superior to partial hippocampectomy (n = 70) and one found ATL to be superior to stereotactic radiosurgery (n = 58); and another provided data to show that for Lennox-Gastaut syndrome, no significant differences in seizure outcomes were evident between those treated with resection of the epileptogenic zone and those treated with resection of the epileptogenic zone plus corpus callosotomy (n = 43). We judged evidence from the nine RCTs to be of moderate to very low quality due to lack of information reported about the randomised trial design and the restricted study populations.Of the 16,756 participants included in this review who underwent a surgical procedure, 10,696 (64%) achieved a good outcome from surgery; this ranged across studies from 13.5% to 92.5%. Overall, we found the quality of data in relation to recording of adverse events to be very poor.In total, 120 studies examined between one and eight prognostic factors in univariate analysis. We found the following prognostic factors to be associated with a better post-surgical seizure outcome: abnormal pre-operative MRI, no use of intracranial monitoring, complete surgical resection, presence of mesial temporal sclerosis, concordance of pre-operative MRI and electroencephalography, history of febrile seizures, absence of focal cortical dysplasia/malformation of cortical development, presence of tumour, right-sided resection, and presence of unilateral interictal spikes. We found no evidence that history of head injury, presence of encephalomalacia, presence of vascular malformation, and presence of postoperative discharges were prognostic factors of outcome.Twenty-nine studies reported multi-variable models of prognostic factors, and showed that the direction of association of factors with outcomes was generally the same as that found in univariate analyses.We observed variability in many of our analyses, likely due to small study sizes with unbalanced group sizes and variation in the definition of seizure outcome, the definition of prognostic factors, and the influence of the site of surgery AUTHORS' CONCLUSIONS: Study design issues and limited information presented in the included studies mean that our results provide limited evidence to aid patient selection for surgery and prediction of likely surgical outcomes. Future research should be of high quality, follow a prospective design, be appropriately powered, and focus on specific issues related to diagnostic tools, the site-specific surgical approach, and other issues such as extent of resection. Researchers should investigate prognostic factors related to the outcome of surgery via multi-variable statistical regression modelling, where variables are selected for modelling according to clinical relevance, and all numerical results of the prognostic models are fully reported. Journal editors should not accept papers for which study authors did not record adverse events from a medical intervention. Researchers have achieved improvements in cancer care over the past three to four decades by answering well-defined questions through the conduct of focused RCTs in a step-wise fashion. The same approach to surgery for epilepsy is required.

Focal epilepsies and focal disorders

Electroencephalographic (EEG) investigations are crucial in the diagnosis and management of patients with focal epilepsies. EEG may reveal different interictal epileptiform discharges (IEDs: abnormal spikes, sharp waves). The EEG visibility of a spike depends on the surface area of cortex involved (>10cm²) and the brain localization of cortical generators. Regions generating IEDs (defining the "irritative zone") are not necessarily equivalent to the seizure onset zone. Focal seizures are dynamic processes originating from one or several brain regions (that generate fast oscillations and are called the epileptogenic zone) before spreading to other structures (that generate lower frequency oscillations and are called the propagation zone). Several factors limit the expression of seizures on scalp EEG, such as the area involved, degree of synchronization, and depth of the cortical generators. Different scalp EEG seizure onset patterns may be observed: fast discharge, background flattening, rhythmic spikes, sinusoidal discharge, or sharp activity. However, to a large extent EEG changes are linked to seizure propagation. Finally, in the context of presurgical evaluation, the combination of interictal and ictal EEG features is crucial to provide an optimal hypothesis concerning the epileptogenic zone.

Lateralization Value of Low Frequency Band Beamformer Magnetoencephalography Source Imaging in Temporal Lobe Epilepsy

Objective: In presurgical evaluation of temporal lobe epilepsy (TLE), selection of the resection side is challenging when bilateral temporal epileptiform discharges or structural abnormalities are present. We aim to evaluate the lateralization value of beamformer analysis of magnetoencephalography (MEG) in TLE. Methods: MEG data from 14 TLE patients were analyzed through beamformer analysis. We measured the hemispherical power distribution of beamformer sources and calculated the lateralization index (LI). We calculated the LI at multiple frequencies to explore the frequency dependency and at the delta frequency to define laterality. LI values ranging from -1 to -0.05 indicated right hemispheric dominance. LI values ranging from 0.05 to 1 indicated left hemispheric dominance. LI values ranging from -0.05 to 0.05 defined bilaterality. We measured the power of beamformer sources with a 9-s duration to explore time dependency. Results: The beamformer analysis showed that 10/14 patients had power dominance ipsilateral to resection. The delta frequency band had a higher lateralization value than other frequency bands. A time-dependent power fluctuation was found in the delta frequency band. Conclusions: MEG beamformer analysis, especially in the delta band, might efficiently provide additional information regarding lateralization in TLE.

Unusual ictal propagation patterns suggesting poor prognosis after temporal lobe epilepsy surgery: Switch of lateralization and bilateral asynchrony

OBJECTIVE

The objective of this study was to investigate unusual ictal propagation patterns in patients with drug-resistant temporal lobe epilepsy (TLE) and reveal their electrophysiological, neuroimaging, and prognostic properties after surgery.

METHODS

Among 248 patients with TLE who underwent scalp video-electroencephalographic (EEG) monitoring, 24 patients with 'switch of lateralization' or 'bilateral asynchrony' in at least one of their seizures (9.3%) were analyzed retrospectively. The postoperative outcome was determined in 16 patients who had undergone epilepsy surgery.

RESULTS

All but 5 of the included patients had hippocampal sclerosis (HS) as their magnetic resonance imaging (MRI) findings. Twelve out of 16 patients (75%) who had surgery were seizure-free for at least 1 year. Nine out of 12 patients (75%) with good outcome had unilateral interictal EEG discharges in temporal regions whereas 3 out of 4 patients with poor outcome had bilateral temporal interictal spiking (p = 0.018).

CONCLUSION

Unusual ictal propagation patterns are not always related to poor prognosis after surgery in patients with TLE. Patients with unilateral interictal spiking in the temporal region tend to have good outcome despite these unusual patterns. These patterns can also be seen in patients with TLE with other etiologies besides the well-known HS in MRI.

Unilateral temporal interictal epileptiform discharges correctly predict the epileptogenic zone in lesional temporal lobe epilepsy

OBJECTIVE

To evaluate the necessity of recording ictal electroencephalography (EEG) in patients with temporal lobe epilepsy (TLE) considered for resective surgery who have unilateral temporal interictal epileptiform discharges (IEDs) and concordant ipsitemporal magnetic resonance imaging (MRI) pathology. To calculate the necessary number of recorded EEG seizure patterns (ESPs) to achieve adequate lateralization probability.

METHODS

In a retrospective analysis, the localization and lateralization of interictal and ictal EEG of 304 patients with lesional TLE were analyzed. The probability of further contralateral ESPs was calculated based on a total of 1967 recorded ESPs, using Bayes' theorem.

RESULTS

Two hundred seventy-one patients had unilateral TLE, and in 98% of them (265 of 271), IEDs were recorded during video-EEG monitoring. Purely unilateral temporal IEDs were present in 61% (166 of 271 patients). Ipsilateral temporal MRI pathology was found in 83% (138 of 166). Ictal EEG was concordant with the clinical side of TLE in 99% (136 of 138) of these patients. Two patients had discordant ictal EEG with both ipsilateral and contralateral ESPs. Epilepsy surgery with resection in the lesioned temporal lobe was still performed, and both patients remain seizure-free. Probability calculations demonstrate that at least 6 recorded unilateral ESPs result in a >95% probability for a concordance of >0.9 of any further ESPs.

SIGNIFICANCE

The combination of purely unilateral temporal IED with ipsitemporal MRI pathology is sufficient to identify the epileptogenic zone, and the recording of ictal ESP did not add any surgically relevant information in these 138 patients. Rarely, discordant ESPs might be recorded, but the surgical outcome remains excellent after surgery on the lesioned side.

Diagnosis of mesial temporal sclerosis: sensitivity, specificity and predictive values of the quantitative analysis of magnetic resonance imaging

In the diagnosis of mesial temporal sclerosis (MTS), sensitivity, specificity and predictive values of qualitative assessment using conventional magnetic resonance imaging are low, mainly in mild or bilateral atrophy. Quantitative analysis may improve this performance. We evaluated the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of quantitative analysis using the hippocampal volumetric index (HVI) and hippocampal asymmetry index (HAI) compared with qualitative assessment in the MTS diagnosis. Twenty-five patients diagnosed with MTS, and 25 healthy subjects underwent conventional magnetic resonance imaging. Hippocampal volumes were obtained using an automated software (FreeSurfer); HVI and HAI were calculated. Receiver operating characteristic curve analysis was performed to obtain the optimal threshold values. Sensitivity, specificity and predictive values were calculated. Sensitivity, specificity, PPV and NPV for qualitative analysis were 44.00%, 96.00%, 91.67% and 63.16%, respectively. In the quantitative analysis, a threshold value of K = 0.22 for HVI provided a sensitivity value of 76.00%, specificity value of 96.00%, PPV of 95.00% and NPV of 80.00%. A threshold value of K = 0.06 for HAI provided the minimum C1 and C2 errors, with a sensitivity value of 88.00%, specificity value of 100%, PPV of 100% and NPV of 89.30%. A statistically significant difference was observed for HAI ( P < 0.0001), and ipsilateral HVI (left MTS, P = 0.0152; right MTS, P < 0.0001), between MTS and healthy groups. The HVI and HAI, both individually and in conjunction, improved the sensitivity, specificity and predictive values of magnetic resonance imaging in the diagnosis of MTS compared to the qualitative analysis and other quantitative techniques. The HAI is highly accurate in the diagnosis of unilateral MTS, whereas the HVI may be better for bilateral MTS cases.

Derivation and initial validation of a surgical grading scale for the preliminary evaluation of adult patients with drug-resistant focal epilepsy

OBJECTIVE

Presently, there is no simple method at initial presentation for identifying a patient's likelihood of progressing to surgery and a favorable outcome. The Epilepsy Surgery Grading Scale (ESGS) is a three-tier empirically derived mathematical scale with five categories: magnetic resonance imaging (MRI), electroencephalography (EEG), concordance (between MRI and EEG), semiology, and IQ designed to stratify patients with drug-resistant focal epilepsy based on their likelihood of proceeding to resective epilepsy surgery and achieving seizure freedom.

METHODS

In this cross-sectional study, we abstracted data from the charts of all patients admitted to the New York University Langone Medical Center (NYULMC) for presurgical evaluation or presented in surgical multidisciplinary conference (MDC) at the NYU Comprehensive Epilepsy Center (CEC) from 1/1/2007 to 7/31/2008 with focal epilepsy, who met minimal criteria for treatment resistance. We classified patients into ESGS Grade 1 (most favorable), Grade 2 (intermediate), and Grade 3 (least favorable candidates). Three cohorts were evaluated: all patients, patients presented in MDC, and patients who had resective surgery. The primary outcome measure was proceeding to surgery and seizure freedom.

RESULTS

Four hundred seven patients met eligibility criteria; 200 (49.1%) were presented in MDC and 113 (27.8%) underwent surgery. A significant difference was observed between Grades 1 and 3, Grades 1 and 2, and Grades 2 and 3 for all presurgical patients, and those presented in MDC, with Grade 1 patients having the highest likelihood of both having surgery and becoming seizure-free. There was no difference between Grades 1 and 2 among patients who had resective surgery.

SIGNIFICANCE

These results demonstrate that by systematically using basic information available during initial assessment, patients with drug-resistant epilepsy may be successfully stratified into clinically meaningful groups with varied prognosis. The ESGS may improve communication, facilitate decision making and early referral to a CEC, and allow patients and physicians to better manage expectations.

Preoperative prediction of temporal lobe epilepsy surgery outcome

PURPOSE

There is controversy about relative contributions of ictal scalp video EEG recording (vEEG), routine scalp outpatient interictal EEG (rEEG), intracranial EEG (iEEG) and MRI for predicting seizure-free outcomes after temporal lobectomy. We reviewed NIH experience to determine contributions at specific time points as well as long-term predictive value of standard pre-surgical investigations.

METHODS

Raw data was obtained via retrospective chart review of 151 patients. After exclusions, 118 remained (median 5 years follow-up). MRI-proven mesial temporal sclerosis (MTSr) was considered a separate category for analysis. Logistic regression estimated odds ratios at 6-months, 1-year, and 2 years; proportional hazard models estimated long-term comparisons. Subset analysis of the proportional hazard model was performed including only patients with commonly encountered situations in each of the modalities, to maximize statistical inference.

RESULTS

Any MRI finding, MRI proven MTS, rEEG, vEEG and iEEG did not predict two-year seizure-free outcome. MTSr was predictive at six months (OR=2.894, p=0. 0466), as were MRI and MTSr at one year (OR=10.4231, p=0. 0144 and OR=3.576, p=0. 0091). Correcting for rEEG and MRI, vEEG failed to predict outcome at 6 months, 1year and 2 years. Proportional hazard analysis including all available follow-up failed to achieve significance for any modality. In the subset analysis of 83 patients with commonly encountered results, vEEG modestly predicted long-term seizure-free outcomes with a proportional hazard ratio of 1.936 (p=0.0304).

CONCLUSIONS

In this study, presurgical tools did not provide unambiguous long-term outcome predictions. Multicenter prospective studies are needed to determine optimal presurgical epilepsy evaluation.

Current and future diagnostic tools for traumatic brain injury: CT, conventional MRI, and diffusion tensor imaging

Brain imaging plays a key role in the assessment of traumatic brain injury. In this review, we present our perspectives on the use of computed tomography (CT), conventional magnetic resonance imaging (MRI), and newer advanced modalities such as diffusion tensor imaging. Specifically, we address assessment for immediately life-threatening intracranial lesions (noncontrast head CT), assessment of progression of intracranial lesions (noncontrast head CT), documenting intracranial abnormalities for medicolegal reasons (conventional MRI with blood-sensitive sequences), presurgical planning for post-traumatic epilepsy (high spatial resolution conventional MRI), early prognostic decision making (conventional MRI with diffusion-weighted imaging), prognostic assessment for rehabilitative planning (conventional MRI and possibly diffusion tensor imaging in the future), stratification of subjects and pharmacodynamic tracking of targeted therapies in clinical trials (specific MRI sequences or positron emission tomography (PET) ligands, e.g., diffusion tensor imaging for traumatic axonal injury). We would like to emphasize that all of these methods, especially the newer research approaches, require careful radiologic-pathologic validation for optimal interpretation. We have taken this approach in a mouse model of pericontusional traumatic axonal injury. We found that the extent of reduction in the diffusion tensor imaging parameter relative anisotropy directly correlated with the number of amyloid precursor protein (APP)-stained axonal varicosities (r(2)=0.81, p<0.0001, n=20 injured mice). Interestingly, however, the least severe contusional injuries did not result in APP-stained axonal varicosities, but did cause reduction in relative anisotropy. Clearly, both the imaging assessments and the pathologic assessments will require iterative refinement.

Predictors of prognosis in patients with temporal lobe epilepsy after anterior temporal lobectomy

The aim of this study was to evaluate the predictive value of prognostic factors for the surgical outcome of patients with mesial temporal lobe epilepsy (MTLE) using Engel seizure classification. The clinical data of 121 patients with MTLE who underwent anterior temporal lobectomy (ATL) and received a 1-year minimum follow-up were collected between January 2005 and December 2008. Patients were divided into seizure and seizure-free groups according to the Engel seizure classification. Univariate analysis and multivariate logistic regression analysis were used to analyze the potential predictive and prognostic factors, including medical history, clinical features of seizures, magnetic resonance imaging (MRI) and video-electroencephalogram (EEG) monitoring results. Univariate analysis indicated no statistically significant differences in gender, age at seizure onset, age at surgery, history of traumatic brain injury, perinatal anoxia, intracranial infection, family history of seizure, auras or site of surgery between the two groups; however, significant differences were detected in pre-surgical seizure duration, history of febrile seizures, seizure types, MRI and video-EEG results. Multivariate logistic regression analysis demonstrated that a pre-surgical seizure duration of <10 years, history of positive febrile seizures, simple complex partial seizure, positive MRI results and unilateral local video-EEG spikes may be considered as predictors of a good prognosis. These results indicate that remission may be achieved in patients with MTLE via the collection of accurate clinical information and adequate pre-surgical evaluation.

Surgery for epilepsy

BACKGROUND

Focal epilepsies are caused by a malfunction of nerve cells localised in one part of one cerebral hemisphere. In studies, estimates of the number of individuals with focal epilepsy who do not become seizure-free despite optimal drug therapy vary according to the age of the participants and which focal epilepsies are included, but have been reported as at least 20% and in some studies up to 70%. If the epileptogenic zone can be located surgical resection offers the chance of a cure with a corresponding increase in quality of life.

OBJECTIVES

The primary objective is to assess the overall outcome of epilepsy surgery according to evidence from randomised controlled trials.The secondary objectives are to assess the overall outcome of epilepsy surgery according to non-randomised evidence and to identify the factors that correlate to remission of seizures postoperatively.

SEARCH METHODS

We searched the Cochrane Epilepsy Group Specialised Register (June 2013), the Cochrane Central Register of Controlled Trials (CENTRAL 2013, Issue 6), MEDLINE (Ovid) (2001 to 4 July 2013), ClinicalTrials.gov and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) for relevant trials up to 4 July 2013.

SELECTION CRITERIA

Eligible studies were randomised controlled trials (RCTs), cohort studies or case series, with either a prospective and/or retrospective design, including at least 30 participants, a well-defined population (age, sex, seizure type/frequency, duration of epilepsy, aetiology, magnetic resonance imaging (MRI) diagnosis, surgical findings), an MRI performed in at least 90% of cases and an expected duration of follow-up of at least one year, and reporting an outcome relating to postoperative seizure control.

DATA COLLECTION AND ANALYSIS

Three groups of two review authors independently screened all references for eligibility, assessed study quality and risk of bias, and extracted data. Outcomes were proportion of participants achieving a good outcome according to the presence or absence of each prognostic factor of interest. We intended to combine data with risk ratios (RR) and 95% confidence intervals.

MAIN RESULTS

We identified 177 studies (16,253 participants) investigating the outcome of surgery for epilepsy. Four studies were RCTs (including one that randomised participants to surgery or medical treatment). The risk of bias in the RCTs was unclear or high, limiting our confidence in the evidence that addressed the primary review objective. Most of the remaining 173 non-randomised studies had a retrospective design; they were of variable size, were conducted in a range of countries, recruited a wide demographic range of participants, used a wide range of surgical techniques and used different scales used to measure outcomes. We performed quality assessment using the Effective Public Health Practice Project (EPHPP) tool and determined that most studies provided moderate or weak evidence. For 29 studies reporting multivariate analyses we used the Quality in Prognostic Studies (QUIPS) tool and determined that very few studies were at low risk of bias across the domains.In terms of freedom from seizures, one RCT found surgery to be superior to medical treatment, two RCTs found no statistically significant difference between anterior temporal lobectomy (ATL) with or without corpus callosotomy or between 2.5 cm or 3.5 cm ATL resection, and one RCT found total hippocampectomy to be superior to partial hippocampectomy. We judged the evidence from the four RCTs to be of moderate to very low quality due to the lack of information reported about the randomised trial design and the restricted study populations.Of the 16,253 participants included in this review, 10,518 (65%) achieved a good outcome from surgery; this ranged across studies from 13.5% to 92.5%. Overall, we found the quality of data in relation to the recording of adverse events to be very poor.In total, 118 studies examined between one and eight prognostic factors in univariate analysis. We found the following prognostic factors to be associated with a better post-surgical seizure outcome: an abnormal pre-operative MRI, no use of intracranial monitoring, complete surgical resection, presence of mesial temporal sclerosis, concordance of pre-operative MRI and electroencephalography (EEG), history of febrile seizures, absence of focal cortical dysplasia/malformation of cortical development, presence of tumour, right-sided resection and presence of unilateral interictal spikes. We found no evidence that history of head injury, presence of encephalomalacia, presence of vascular malformation or presence of postoperative discharges were prognostic factors of outcome. We observed variability between studies for many of our analyses, likely due to the small study sizes with unbalanced group sizes, variation in the definition of seizure outcome, definition of the prognostic factor and the influence of the site of surgery, all of which we observed to be related to postoperative seizure outcome. Twenty-nine studies reported multivariable models of prognostic factors and the direction of association of factors with outcome was generally the same as found in the univariate analyses. However, due to the different multivariable analysis approaches and selective reporting of results, meaningful comparison of multivariate analysis with univariate meta-analysis is difficult.

AUTHORS' CONCLUSIONS

The study design issues and limited information presented in the included studies mean that our results provide limited evidence to aid patient selection for surgery and prediction of likely surgical outcome. Future research should be of high quality, have a prospective design, be appropriately powered and focus on specific issues related to diagnostic tools, the site-specific surgical approach and other issues such as the extent of resection. Prognostic factors related to the outcome of surgery should be investigated via multivariable statistical regression modelling, where variables are selected for modelling according to clinical relevance and all numerical results of the prognostic models are fully reported. Protocols should include pre- and postoperative measures of speech and language function, cognition and social functioning along with a mental state assessment. Journal editors should not accept papers where adverse events from a medical intervention are not recorded. Improvements in the development of cancer care over the past three to four decades have been achieved by answering well-defined questions through the conduct of focused RCTs in a step-wise fashion. The same approach to surgery for epilepsy is required.

Surgical outcome in patients with MRI-negative, PET-positive temporal lobe epilepsy

PURPOSE

The purpose of this study was to determine the long-term surgical outcomes of magnetic resonance imaging (MRI)-negative, fluorodeoxyglucose positron emission tomography (FDG-PET)-positive patients with temporal lobe epilepsy (TLE) and compare them with those of patients with mesial temporal sclerosis (MTS).

METHODS

One hundred forty-one patients with TLE who underwent anterior temporal lobectomy were included in the study. The surgical outcomes of 24 patients with unilateral temporal hypometabolism on FDG-PET without an epileptogenic lesion on MRI were compared with that of patients with unilateral temporal hypometabolism on FDG-PET with MTS on MRI (n=117). The outcomes were compared using Engel's classification at 2 years after surgery. Clinical characteristics, unilateral interictal epileptiform discharges (IEDs), histopathological data and operation side were considered as probable prognostic factors.

RESULTS

Class I surgical outcomes were similar in MRI-negative patients and the patients with MTS on MRI (seizure-free rate at postoperative 2 years was 79.2% and 82% in the MRI-negative and MTS groups, respectively). In univariate analysis, history of febrile convulsions, presence of unilateral IEDs and left temporal localization were found to be significantly associated with seizure free outcome. Multivariate analysis revealed that independent predictors of a good outcome were history of febrile convulsions and presence of unilateral IEDs.

CONCLUSION

Our results suggest that epilepsy surgery outcomes of MRI-negative, PET positive patients are similar to those of patients with MTS. This finding may aid in the selection of best candidates for epilepsy surgery.

EEG-fMRI evaluation of patients with mesial temporal lobe sclerosis

This preliminary study sought more information on blood oxygen level dependent (BOLD) activation, especially contralateral temporal/extratemporal spread, during continuous EEG-fMRI recordings in four patients with mesial temporal sclerosis (MTS). In two patients, EEG showed unilateral focal activity during the EEG-fMRI session concordant with the interictal focus previously identified with standard and video-poly EEG. In the other two patients EEG demonstrated a contralateral diffusion of the irritative focus. In the third patient (with the most drug-resistant form and also extratemporal clinical signs), there was an extratemporal diffusion over frontal regions, ipsilateral to the irritative focus. fMRI analysis confirmed a single activation in the mesial temporal region in two patients whose EEG showed unilateral focal activity, while it demonstrated a bilateral activation in the mesial temporal regions in the other two patients. In the third patient, fMRI demonstrated an activation in the supplementary motxor area. This study confirms the most significant activation with a high firing rate of the irritative focus, but also suggests the importance of using new techniques (such as EEG-fMRI to examine cerebral blood flow) to identify the controlateral limbic activation, and any other extratemporal activations, possible causes of drug resistance in MTS that may require a more precise pre-surgical evaluation with invasive techniques.

Anterior temporal lobectomy with amygdalohippocampectomy for mesial temporal sclerosis: predictors of long-term seizure control

Object

In this paper the authors' goal was to identify preoperative variables that predict long-term seizure freedom among patients with mesial temporal sclerosis (MTS) after single-stage anterior temporal lobectomy and amygdalohippocampectomy (ATL-AH).

Methods

The authors retrospectively reviewed 116 consecutive patients (66 females, mean age at surgery 40.7 years) with refractory seizures and pathologically confirmed MTS who underwent ATL-AH with at least 2 years of follow-up. All patients underwent preoperative MRI and video-electroencephalography (EEG); 106 patients (91.4%) underwent Wada testing and 107 patients (92.2%) had neuropsychological evaluations. The authors assessed the concordance of these 4 studies (defined as test consistent with the side of eventual surgery) and analyzed the impact of preoperative variables on seizure freedom.

Results

The median follow-up after surgery was 6.7 years (mean 6.9 years). Overall, 103 patients (89%) were seizure free, and 109 patients (94%) had Engel Class I or II outcome. Concordant findings were highest for video-EEG (100%), PET (100%), MRI (99.0%), and Wada testing (90.4%) and lowest for SPECT (84.6%) and neuropsychological testing (82.5%). Using binary logistic regression analysis (seizure free or not) and Cox proportional hazard analysis (seizure-free survival), less disparity in the Wada memory scores between the ipsilateral and contralateral sides was associated with persistent seizures.

Conclusions

Seizure freedom of nearly 90% can be achieved with ATL-AH in properly selected patients with MTS and concordant preoperative studies. The low number of poor outcomes and exclusion of multistage patients limit the statistical power to determine preoperative variables that predict failure. Strong Wada memory lateralization was associated with excellent long-term outcome and adds important localization information to structural and neurophysiological data in predicting outcome after ATL-AH for MTS.

Presurgical lateralization of seizure focus in temporal lobe epilepsy with noninvasive imaging

We retrospectively compared the seizure focus-localizing capability of interictal PET/CT to that of interictal magnetic resonance diffusion-weighted imaging and ictal SPECT in 21 patient candidate for neurosurgery with temporal lobe epilepsy (TLE) by assessing overall lateralizing ability of these modalities and concordance of findings on these studies with results of electroencephalography (EEG). PET/CT demonstrated the greatest lateralizing ability of any of the imaging modalities and had the highest concordance rate for lateralization with EEG, highlighting its increasing diagnostic utility in the preoperative imaging workup of patients with medically intractable TLE.

Seizure outcomes and mesial resection volumes following selective amygdalohippocampectomy and temporal lobectomy

OBJECT

Anterior temporal lobectomy (ATL) and selective amygdalohippocampectomy (SelAH) are the preferred surgical approaches for the treatment of medically refractory epilepsy involving the nondominant and dominant temporal lobes, respectively. Both techniques provide access to mesial structures-with the ATL providing a wider surgical corridor than SelAH. Because the extent of mesial temporal resection potentially impacts seizure outcome, the authors examined mesial resection volumes, seizure outcomes, and neuropsychiatric test scores in patients undergoing either ATL or transcortical SelAH at a single institution.

METHODS

A retrospective study was conducted in 96 patients with medically refractory mesial temporal lobe epilepsy. Fifty-one patients who had nondominant temporal lobe epilepsy underwent standard ATL, and 45 patients with language-dominant temporal lobe epilepsy underwent transcortical SelAH. Volumetric MRI analysis was used to quantify the mesial resection in both groups. In addition, the authors examined seizure outcomes and the change in neuropsychiatric test scores.

RESULTS

Seizure-free outcome in the entire patient cohort was 94% at a mean follow-up of 44 months. There was no significant difference in the seizure outcome between the 2 groups. The extent of resection of the mesial structures following ATL was slightly higher than for SelAH (98% vs. 91%, p < 0.0001). The change in neuropsychiatric test scores largely reflected the side of surgery, but overall IQ and memory function did not change significantly in either group.

CONCLUSIONS

Transcortical SelAH provides adequate access to the mesial structures, and allows for a resection that is nearly as extensive as that achieved with standard ATL. Seizure outcomes and neuropsychiatric sequelae are similar in both procedures.

EEG-fMRI validation studies in comparison with icEEG: a review

Simultaneous EEG-fMRI is a non-invasive investigation technique developed to localize the generators of interictal epileptiform discharges (IED) in patients with epilepsy. Although the value of EEG-fMRI in epilepsy presurgical evaluation is being assessed clinically, its utility is still controversial. In this review, we considered EEG-fMRI applications in epilepsy presurgical evaluation with a focus on validation studies that compared the results of EEG-fMRI with those of the current "gold standard" intracranial EEG (icEEG) in order to assess its utility of seizure focus localization and the possibility for EEG-fMRI to reduce the need for invasive techniques such as icEEG. Since the advances of EEG-fMRI partially rely on the maturation of its data analysis, we also reviewed the methodological developments in EEG-fMRI analysis. It is possible that combining with other neuroimaging modalities such as MEG/MSI and ESI, EEG-fMRI may play a greater role in epilepsy presurgical evaluation.

Vagal nerve stimulation: exploring its efficacy and success for an improved prognosis and quality of life in cerebral palsy patients

Cerebral palsy (CP) continues to pose a cause for major socioeconomic concern and medical challenge worldwide. It is associated with a multi-faceted symptomatology warranting a multi-dimensional management-approach. Recent recognition of neurocognitive impairment and its hopefully possible treatment has opened up a new dimension in its management to the neurologists. Vagal nerve stimulation (VNS) technique is presently emerging as an effective alternative anti-epileptic therapeutic measure in intractable epilepsy. VNS has recently been shown to possess a suppressive effect also on interictal epileptiform discharges (IEDs) that are now being widely accepted as established associates of neurocognitive impairment. In this paper, the author proposes VNS technique implantation in CP patients on account of its dual therapeutic effectiveness, i.e. anti-epileptic and IED-suppression. These two effects are likely to control seizures that are quite often drug-resistant and also improve neurocognition in CP patients, thus hoping for a better overall prognostic outcome and an improved quality of life of the CP patients by VNS.

Functional imaging in temporal lobe epilepsy

This article highlights the importance of functional imaging methods in the diagnosis and preoperative planning in temporal lobe epilepsy TLE). It starts with a discussion of the role of ictal and interictal single-photon emission computed tomography (SPECT) and interictal positron emission tomography (PET) in lateralizing TLE. The next section discusses the role of blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) and perfusion MRI, particularly for lateralization of language and memory in TLE patients. The final section explores the relatively new role that the emerging technique of diffusion tensor imaging (DTI) is playing in the evaluation of TLE.

Magnetoencephalography Is More Successful for Screening and Localizing Frontal Lobe Epilepsy than Electroencephalography

PURPOSE

The diagnosis of frontal lobe epilepsy may be compounded by poor electroclinical localization, due to distributed or rapidly propagating epileptiform activity. This study aimed at developing optimal procedures for localizing interictal epileptiform discharges (IEDs) of patients with localization related epilepsy in the frontal lobe. To this end the localization results obtained for magnetoencephalography (MEG) and electroencephalography (EEG) were compared systematically using automated analysis procedures.

METHODS

Simultaneous recording of interictal EEG and MEG was successful for 18 out of the 24 patients studied. Visual inspection of these recordings revealed IEDs with varying morphology and topography. Cluster analysis was used to classify these discharges on the basis of their spatial distribution followed by equivalent dipole analysis of the cluster averages. The locations of the equivalent dipoles were compared with the location of the epileptogenic lesions of the patient or, if these were not visible at MRI with the location of the interictal onset zones identified by subdural electroencephalography.

RESULTS

Generally IEDs were more abundantly in MEG than in the EEG recordings. Furthermore, the duration of the MEG spikes, measured from the onset till the spike maximum, was in most patients shorter than the EEG spikes. In most patients, distinct spike subpopulations were found with clearly different topographical field maps. Cluster analysis of MEG spikes followed by dipole localization was successful (n = 14) for twice as many patients as for EEG source analysis (n = 7), indicating that the localizability of interictal MEG is much better than of interictal EEG.

CONCLUSIONS

The automated procedures developed in this study provide a fast screening method for identifying the distinct categories of spikes and the brain areas responsible for these spikes. The results show that MEG spike yield and localization is superior compared with EEG. This finding is of importance for the diagnosis and preoperative evaluation of patients with frontal lobe epilepsy.

Outcome following surgery for temporal lobe epilepsy with hippocampal involvement in preadolescent children: emphasis on mesial temporal sclerosis

OBJECT

The authors conducted a multiinstitutional, retrospective analysis to better define outcome and prognostic indicators for temporal lobe epilepsy surgery for suspected mesial temporal sclerosis (MTS) in young children.

METHODS

Data were collected for all children undergoing temporal resections at four epilepsy centers over approximately 10 years. Children with a histopathological diagnosis of neoplasm were excluded. Forty-nine patients (28 boys and 21 girls) were included in the study. Their mean age at surgery was 9.1 years (range 1.25-13.9 years). The mean age at seizure onset was 3.2 years (range birth-10 years). Histopathological examination demonstrated MTS in 26 cases, gliosis in nine, dysplasia in five, gliosis with dysplasia in four, and nonspecific or normal findings in five. Forty-one anterior temporal lobectomies (nine tailored) and eight selective amygdalohippocam-pectomies were performed (28 left side, 21 right side). Twenty-nine children (59.2%) underwent invasive monitoring. Operative complications included extraaxial hematomas (two cases), cerebrospinal fluid leaks (two cases), and hydrocephalus (one case), each in children undergoing invasive monitoring. The mean duration of follow up was 26.4 months (range 5-74 months) overall and 23.9 months (range 6-74 months) for the Engel Class I subgroup. Outcomes at the most recent follow-up examination were categorized as Engel Class I-II in 31 (63.3%) of 49 children overall, 20 (76.9%) of 26 children with confirmed MTS, four (36.4%) of 11 children with gliosis, and four (57.1%) of seven children with dysplasia. All patients who underwent selective amygdalohippocampectomies had confirmed MTS and Engel Class I outcomes. Patients with more than one seizure type (p = 0.048) or moderate to severe developmental delay (p = 0.03) had significantly worse outcomes (Engel Class III or IV). Age at seizure onset, age at surgery, and duration of seizure disorder were not significantly related to outcome. There was a trend for bilateral or extratemporal findings on electroencephalography (EEG) (p = 0.157), high preoperative seizure frequency (p = 0.097), and magnetic resonance (MR) imaging findings inconsistent with MTS (p = 0.142) to be associated with worse outcome, although it did not reach statistical significance. In only 12 (46.1%) of the 26 patients with confirmed MTS was the condition prospectively diagnosed on preoperative MR imaging.

CONCLUSIONS

Younger children with temporal lobe epilepsy have satisfying surgical outcomes, particularly when MTS is present. Magnetic resonance imaging may not be as sensitive in detecting MTS in children as in older patients. Negative predictors identified include multiple seizure types and preoperative developmental delay. Multifocal or bilateral EEG findings, high preoperative seizure frequency, and MR imaging findings inconsistent with MTS also independently suggested worse outcome.

Treatment of interictal epileptiform discharges in cerebral palsy patients without clinical epilepsy: hope for a better outcome in prognosis

Cerebral palsy (CP) is a motor disorder due to cerebral damage. It is commonly associated with neuro-psychological retardation and also with epilepsy; hence, its management warrants a multi-dimensional approach. In a significant number of CP patients, interictal epileptiform discharges (IEDs) are obtained in their EEG even in absence of clinical epilepsy. Epileptiform discharge-firing cortical neurons are found to be associated with elevated intracellular Ca(2+) levels and exhibition of abnormal response on exposure to excitotoxic glutamate; both these features have been found to lead to subsequent death of these neurons. This further damage is likely to aggravate the already existing cortical damage in CP patients thereby worsening their prognosis. IEDs are also known to be associated with other neuro-psychological disorders like cognitive impairment and behavioral problems even in absence of clinical epilepsy. Thus, the IEDs cannot be viewed as benign events and their occurrence even in absence of clinical epilepsy cannot be ignored. A few trials aimed at treating IEDs in autistic patients without epilepsy and in children with behavior problems have yielded favorable results. Based on these studies, the author proposes inclusion of EEG investigation in the management protocol of CP patients and treatment of IEDs (when detected even in absence of clinical epilepsy) for a better outcome in their prognosis.

Complete change of seizure and spike lateralization in temporal lobe epilepsy at two separate monitorings

OBJECTIVE

To report complete change of seizure and spike lateralization over time in bilateral temporal lobe epilepsies (TLE).

METHODS

Repetition of video-EEG monitorings in 115 patients; 2 cases are reported in detail; 113 other severe partial epilepsies were included to estimate retrospectively the frequency of the reported phenomenon.

RESULTS

In 2 cases, two video-EEG monitorings, separated by several months, revealed the first time one unilateral TL (temporal lobe) seizure and spike focus and the second time a distinct seizure and spike focus located in the opposite TL. The second monitoring was planned for these two patients because of the presence of a discordant lesion or, in the absence of a lesion, of some bilateral or discordant functional (EEG, SPECT and PET) abnormalities. No patient among the other 113 cases had this video-EEG pattern.

CONCLUSIONS

In TLE, two video-EEG sessions may be necessary to disclose two opposite TL epileptogenic foci.

SIGNIFICANCE

In rare bilateral TLE cases, the expression of seizure and spike foci can alternate between hemispheres.

Surgical outcome in patients with refractory epilepsy associated to MRI-defined unilateral mesial temporal sclerosis

INTRODUCTION: Several pre-operative work-up protocols have been used while selecting epileptic patients for surgery among different centers. The relative value of the different available pre-operative tests is still under discussion. OBJECTIVE: We report on the surgical outcome obtained in patients with refractory temporal lobe epilepsy associated to mesial temporal sclerosis (MTS) and who were evaluated pre-operatively by interictal EEG and MRI alone. METHOD: Forty one patients with refractory unilateral temporal lobe epilepsy were evaluated using interictal EEG and MRI. MRI disclosed unilateral MTS in all patients. All patients had at least 4 interictal EEG recordings. All patients were submitted to cortico-amygdalo-hippocampectomy at the side determined by MRI. RESULTS: Interictal EEG showed unilateral epileptiform discharges compatible with MRI findings in 37 patients; in four out of the 41 patients, bilateral discharges were found. Mean follow-up time was 4.3±1.1 years. Thirty-nine patients (95.1%) were classified as Engel’s Class I (70.6% Engel I-A). Two patients (4.9%) were rated as Engel's Class II. All patients in whom bilateral discharges were found were in Engel’s Class I. Pathological examination showed MTS in all patients. CONCLUSION: It is possible to adequately select good surgical candidates for temporal lobe resection using MRI and interictal EEG alone. In patients with MRI-defined MTS we should expect a postoperative remission rate higher then 90%. The finding of MTS on MRI is the most important good prognostic factor after temporal lobe resection.

Treatment options and paradigms in childhood temporal lobe epilepsy

Temporal lobe epilepsy in adults is a relatively homogenous syndrome with hippocampal sclerosis being its most common pathologic substrate. In the pediatric age group, low-grade neoplasms and cortical dysplasia are much more common than hippocampal sclerosis. Pediatric temporal lobe epilepsy has distinct semiologic, electrophysiologic and imaging characteristics as compared with its adult counterpart. The various treatment options for pediatric temporal lobe epilepsy include antiepileptic drugs, resective surgery, vagal nerve stimulation and the ketogenic diet. In spite of the multiple antiepileptic drugs currently available, 5-10% of all newly diagnosed cases will remain intractable to medical therapy and should be referred for presurgical evaluation. Resective surgery offers the best chance of seizure freedom in carefully selected patients. Future areas of research include new drug development, better imaging and localization techniques, and brain stimulation.

Intracranial EEG substrates of scalp EEG interictal spikes

PURPOSE

To determine the area of cortical generators of scalp EEG interictal spikes, such as those in the temporal lobe epilepsy.

METHODS

We recorded simultaneously 26 channels of scalp EEG with subtemporal supplementary electrodes and 46 to 98 channels of intracranial EEG in 16 surgery candidates with temporal lobe epilepsy. Cerebral discharges with and without scalp EEG correlates were identified, and the area of cortical sources was estimated from the number of electrode contacts demonstrating concurrent depolarization.

RESULTS

We reviewed approximately 600 interictal spikes recorded with intracranial EEG. Only a very few of these cortical spikes were associated with scalp recognizable potentials; 90% of cortical spikes with a source area of >10 cm(2) produced scalp EEG spikes, whereas only 10% of cortical spikes having <10 cm(2) of source area produced scalp potentials. Intracranial spikes with <6 cm(2) of area were never associated with scalp EEG spikes.

CONCLUSIONS

Cerebral sources of scalp EEG spikes are larger than commonly thought. Synchronous or at least temporally overlapping activation of 10-20 cm(2) of gyral cortex is common. The attenuating property of the skull may actually serve a useful role in filtering out all but the most significant interictal discharges that can recruit substantial surrounding cortex.

Self-reported Seizure Frequency and Time to First Event in the Seizure Monitoring Unit

PURPOSE

To compare seizure frequency reported in the clinic with time to first diagnostic event during video-EEG monitoring. The effect of the artificial environment of the monitoring unit on self-reported seizure frequency was explored.

METHODS

The 155 consecutive patients were seen in the Washington University Epilepsy Center and subsequently underwent video-EEG monitoring during 2001. Of these, 112 had a diagnostic event during monitoring; 31 left without having a definite event; and 12 could not provide an estimate of seizure frequency in the clinic. The time to first event was compared with self-reported seizure frequency. The patients were then divided into three equal groups (tertiles) based on mean seizure frequency, and time to first seizure was compared between groups. Then the numbers of patients staying >7 days without ever having an event were compared between the low and high seizure-frequency groups. Finally, Kaplan-Meier survival curves were calculated.

RESULTS

No correlation was found between self-reported seizure rate and time to diagnostic event (r= 0.18; p = 0.06). Time to first event was 2.8 days in the low seizure-frequency group (mean, 2.2/month), 2.1 days in the medium (mean, 8.8/month), and 2.1 days in the high (mean, 24.1/month) groups, which were not significantly different (p = 0.19). Of patients in the low-frequency group, 79% had an event within 7 days.

CONCLUSIONS

In the artificial environment of the monitoring unit, self-reported outpatient seizure frequency is not an accurate predictor of duration of video-EEG monitoring required to make a definitive classification of clinical events and should not contribute to the decision as to whether to refer a patient for monitoring.

Epilepsy surgery with intraoperative MRI at 1.5 T

Despite the infancy of iMRI in epilepsy surgery and the paucity of literature on this topic, some conclusions may be reached. Although iMRI is a useful adjunct during epilepsy procedures, a randomized control trial is necessary to determine its true impact.

Predictors of epilepsy surgery outcome: a meta-analysis

The potential efficacy of temporal and extratemporal resection in patients with partial epilepsy uncontrolled by anti-epileptic drugs is undisputed. However, there are still uncertainties about which patients will benefit most. A systematic review of the available literature has been undertaken by four pairs of reviewers to assess the overall outcome of epilepsy surgery and to identify factors better correlated to seizure outcome. A Medline search for studies on epilepsy surgery published since 1984 was performed. Studies were included if they had a well-defined population and design, a sample size of at least 30 patients, an MRI performed in least 90% of cases, an expected duration of follow-up of at least one year, and a post-operative outcome measured as seizure remission. A good outcome was considered as seizure control or seizure-free status for at least one year or Engel class I. Based on the review of 47 articles meeting all the eligibility criteria, febrile seizures (odds ratio, OR, 0.48; 95% confidence interval, CI, 0.27-0.83), mesial temporal sclerosis (OR 0.47; 95% CI 0.35-0.64), tumors (OR 0.58; 95% CI 0.42-0.80), abnormal MRI (OR 0.44; 95% CI 0.29-0.65), EEG/MRI concordance (OR 0.52; 95% CI 0.32-0.83), and extensive surgical resection (OR 0.24; 95% CI 0.16-0.36) were the strongest prognostic indicators of seizure remission (positive predictors); by contrast, post-operative discharges (OR 2.41; 95% CI 1.37-4.27) and intracranial monitoring (OR 2.72; 95% CI 1.60-4.60) predicted an unfavorable prognosis (negative predictors). Firm conclusions cannot be drawn for extent of resection, EEG/MRI concordance and post-operative discharges for the heterogeneity of study results. Neuromigrational defects, CNS infections, vascular lesions, interictal spikes, and side of resection did not affect the chance of seizure remission after surgery. Despite a number of limitations, the results of the review provide some insight into the selection of the best surgical candidates in clinical practice but raise concerns on the quality of published reports, and may serve as the basis for the identification of better standards to assess surgical outcome in observational studies.

Lesional mesial temporal lobe epilepsy and limited resections: prognostic factors and outcome

OBJECTIVES

To evaluate the influence of clinical, investigational, surgical, and histopathological factors on postoperative seizure relief in patients with mesial temporal lobe epilepsy (MTLE) due to lesions other than ammonshornsclerosis (AHS).

METHODS

Of 738 patients operated for TLE, 78 patients underwent limited resections for lesional MTLE (1990-2000). Seventy four patients with a follow up of more than one year were included. The preoperative clinical, neuropsychological, electroencephalogram, and neuroimaging characteristics were prospectively collected in a database. The histopathological material was re-examined.

RESULTS

The mean follow up was 49 months. Fifty eight patients were classified as seizure free (78.4% Class I), and six as almost seizure free (8.1% Class II), grouped together as satisfactory seizure control (64 patients, 86.5%). Five patients (6.8%) were categorised in Classes III and IV, respectively. These were grouped as unsatisfactory seizure control (10 patients, 13.5%). Surgical procedures were: 32 amygdalohippocampectomies (AH), 17 partial anterior AH, 15 AH plus polar resection, seven AH plus basal resection, and three AH plus extended temporal lesionectomy. There was no mortality and 2.7% mild permanent morbidity. Seizure relief did neither differ significantly with these approaches, nor with different classes of pathological findings (43 developmental tumours, 12 glial tumours, 10 dysplasias, and nine others). Even operation of dysplasias resulted in 80% satisfactory seizure control. Seizure onset during childhood proved to be a negative predictor for seizure relief (p = 0.020). MRI revealed 73 suspected lesions (98.6%), one dysembryoplastic neuroepithelial tumour was missed, in four cases no structural abnormalities could be confirmed with histopathological exam. Additionally, multifactorial regression revealed the factors "seizure onset after 10 years of age", "presence of complex partial seizures", "absence of a neurological deficit", and a "correlating neuropsychological deficit" as predictive for satisfactory seizure control.

CONCLUSIONS

"Preoperative tailoring" resulting in limit resections has proven to be safe and to provide a very good chance for satisfactory seizure relief in patients with lesional MTLE.

Bilateral mesial temporal lobe epilepsy: comparison of scalp EEG and hippocampal MRI-T2 relaxometry

OBJECTIVE

Bilateral hippocampal abnormality is frequent in mesial temporal lobe sclerosis and might affect outcome in epilepsy surgery. The objective of this study was to compare the lateralization of interictal and ictal scalp EEG with MRI T2 relaxometry.

MATERIAL AND METHODS

Forty-nine consecutive patients with intractable mesial temporal lobe epilepsy (MTLE) were studied with scalp EEG/video monitoring and MRI T2 relaxometry.

RESULTS

Bilateral prolongation of hippocampal T2 time was significantly associated with following bitemporal scalp EEG changes: (i) in ictal EEG left and right temporal EEG seizure onsets in different seizures, or, after regionalized EEG onset, evolution of an independent ictal EEG over the contralateral temporal lobe (left and right temporal asynchronous frequencies or lateralization switch; P = 0.002); (ii) in interictal EEG both left and right temporal interictal slowing (P = 0.007). Bitemporal T2 changes were not, however, associated with bitemporal interictal epileptiform discharges (IED). Lateralization of bilateral asymmetric or unilateral abnormal T2 findings were associated with initial regionalization of the ictal EEG in all but one patient (P < 0.005), with lateralization of IED in all patients (P < 0.005), and with scalp EEG slowing in 28 (82,4%) of 34 patients (P = 0.007).

CONCLUSION

Our data suggest that EEG seizure propagation is more closely related to hippocampal T2 abnormalities than IED. Interictal and ictal scalp EEG, including the recognition of ictal propagation patterns, and MRI T2 relaxometry can help to identify patients with bitemporal damage in MTLE. Further studies are needed to estimate the impact of bilateral EEG and MRI abnormal findings on the surgical outcome.

Analysis of different types of resection for pediatric patients with temporal lobe epilepsy

OBJECTIVE

Resection strategies for the treatment of temporal lobe epilepsy (TLE) are a matter of discussion. Few data on the significance of resection type are available for pediatric patients with TLE.

METHODS

Data for a series of 89 children who were surgically treated for TLE were analyzed. A first cohort of patients were mainly surgically treated with anterior temporal lobectomies. For a second cohort, resections were preoperatively "tailored" to the lesion and presumed epileptogenic area.

RESULTS

The follow-up period was 46 months (range, 14-118 mo). Seventy-seven patients (87%) attained satisfactory seizure control (82% Engel Class I and 5% Class II). For 12 patients (13%), seizure control was unsatisfactory (8% Class III and 5% Class IV). Anterior temporal lobectomies resulted in 94% satisfactory seizure control (33 patients), whereas the success rates were only 74% (20 patients) for amygdalohippocampectomy (AH) (P = 0.023) and 77% (13 patients) for lesionectomy plus hippocampectomy (not significant). All patients who underwent purely lateral temporal lesionectomies became seizure-free (14 patients). Logistic regression revealed the factors of AH (P = 0.021) and left-side surgery (P = 0.017) as significant predictors of unsatisfactory seizure control. Satisfactory seizure control was not dependent on the histopathological diagnoses. There was a low rate of verbal memory deterioration after left-side operations. Neuropsychological deterioration was rare after right temporal resections. Attentional and contralateral functions improved after surgery.

CONCLUSION

Surgery for the treatment of juvenile TLE is successful and safe, but the resection type may influence outcomes. Results after AHs were disappointing, probably because of difficulties in precise localization of the epileptogenic focus among children. Neuropsychological results demonstrated minimal rates of deterioration and significant improvements in contralateral functions. Surgical treatment of juvenile TLE should be encouraged, but the use of especially left AH should possibly be restricted.

Unilateral Hippocampal Sclerosis with Contralateral Temporal Scalp Ictal Onset

PURPOSE

To investigate the clinical characteristics and surgical outcomes in patients with unilateral hippocampal sclerosis whose scalp ictal EEG recordings localize to the opposite temporal lobe.

METHODS

We retrospectively reviewed the data of all adult patients who had undergone depth electrode implantation for suspected temporal lobe epilepsy (TLE) at UCLA (1993-2000) or the Montreal Neurological Institute (1991-1998) to identify patients who had (a) unilateral hippocampal atrophy, and (b) surface ictal recordings in which the majority of seizures appeared to initiate in the opposite temporal lobe, with few or none that were concordant with the hippocampal atrophy.

RESULTS

Of 109 patients with suspected TLE who underwent depth electrode study at the two centers, five patients met the aforementioned criteria. Four of these five had very severe hippocampal atrophy, whereas the fifth had mild atrophy but extensive signal change on magnetic resonance imaging (MRI). Depth electrode recordings in four of the five patients yielded clear ictal onset in the mesial temporal lobe ipsilateral to the imaging abnormality (contralateral to apparent scalp ictal onset). One patient had an unusual bitemporal onset pattern, which was nonetheless suggestive of onset in the sclerotic hippocampus. No patient had intracranial ictal onset contralateral to the imaging abnormality. All patients underwent resection of the structurally abnormal temporal lobe. After follow-up of > or = 2 years, four (80%) of five patients were seizure free, while the fifth showed lesser improvement (class III).

CONCLUSIONS

Some patients with severe hippocampal sclerosis (sometimes called a "burned-out hippocampus") have atypical spread of ictal discharges, resulting in apparent gross discordance between imaging and scalp ictal recordings. These patients nonetheless have excellent surgical outcomes on the whole. Whether such patients may forego intracranial recordings requires further study.

Value of extent of hippocampal resection in the surgical treatment of temporal lobe epilepsy

OBJECTIVE: Unilateral hippocampal atrophy is indicator of good surgical prognosis in patients with temporal lobe epilepsy (TLE). Some patients however do not become seizure free after surgery. We assessed if the extent of hippocampal and amygdala resection is associated with outcome. METHODS: Thirty patients with TLE with unilateral or clearly asymmetric hippocampal atrophy who underwent surgical treatment were evaluated concerning preoperative clinical variables and interictal EEG abnormalities. Amygdala and hippocampal resection was evaluated by post-operative MRI. We compared seizure free versus non-seizure free patients, and patients with good outcome (Engel's classes I and II) versus patients with poor outcome. RESULTS: There was significant association between the extent of hippocampal resection and the outcome. Pre-operative variables and interictal EEG abnormalities did not show relationship with outcome as documented in previous studies. CONCLUSION: The extent of hippocampal resection is associated with outcome. Incomplete resection of atrophic hippocampus may explain most surgical failures in patients with TLE due to unilateral hippocampal sclerosis.

Lateralization of Epileptic Foci by Neuropsychological Testing in Mesial Temporal Lobe Epilepsy

This study investigated the lateralizing value of neuropsychological testing in presurgical evaluation of mesial temporal lobe epilepsy (MTLE). This study differed from previous ones in that the cutoff values were determined to yield high positive predictive values (PPVs), multiple neuropsychological predictors were considered in combination, and patients with atypical language dominance or low intelligence were not excluded from the sample. The participants were 92 patients with MTLE (left, n = 47; right, n = 45) who showed good postoperative seizure control. With a stringent cutoff criterion, the multiple neuropsychological predictors considered in combination yielded a sensitivity of 15% and a PPV of 93%, and with a less stringent cutoff criterion, a sensitivity of 37% and a PPV of 83%.

Chapter 39 Current role of EEG in the presurgical evaluation of temporal lobe epilepsy patients

Despite all new developments in methodologies to investigate epileptic patients, EEG continues to play a central and irreplaceable role in clinical epileptology, especially in the presurgical evaluation of medically intractable epilepsies. Temporal lobe epilepsy is the most prevalent type of epileptic syndrome, and also the most frequent type of surgically treatable epilepsy. Non-invasive and invasive EEG methodologies are essential in the selection of surgical candidates. More recently there has been a trend towards the use of exclusively noninvasive methodologies. In this chapter we describe our current view on the role of diverse EEG methodologies in the presurgical evaluation of mesial temporal lobe epilepsies, addressing, in particular, the role of foramen ovale electrodes which, probably, needs to be reassessed in view of the unprecedented evolution of MRI.