Long-term surgical outcomes in patients with drug-resistant temporal lobe epilepsy and no histological abnormalities

INTRODUCTION

Reports on surgical outcomes in patients with drug-resistant temporal lobe epilepsy without histological abnormalities are scarce.

METHODS

Retrospective review of data from patients with drug-resistant temporal lobe epilepsy and no histopathological alterations who underwent anterior mesial temporal lobectomy. We analysed the following variables: age, sex, age at seizure onset, age at surgery, time elapsed between diagnosis and the date of the surgery, follow-up time, and classification according to the Engel rating scale.

RESULTS

From a database of 256 temporal lobectomies, 21 were identified as meeting the inclusion criteria. The average age upon diagnosis of epilepsy was 8.3 years and average age at time of surgery was 28.6 years. The mean time elapsed between diagnosis and surgery was 20.2 years. After a mean follow-up of 6.5 years, 90.5% of the patients showed favourable outcomes (classes i and ii) and 42.9% were seizure-free (class IA). Comparative analysis of the variables revealed that average age at seizure onset was the only statistically significant difference between groups, with age at onset being lower in patients with favourable outcomes.

CONCLUSION

Although long-term surgical outcomes were favourable for a large majority of patients, the percentage of seizure-free patients is lower than in patients with lesional epilepsy and comparable to that previously reported in the literature.

Radial microcolumnar cortical architecture: maturational arrest or cortical dysplasia?

The fetal neocortical plate, from initiation of radial migration at 5 weeks' gestation until midgestation, exhibits radial microcolumnar architecture. Horizontal histologic layering or lamination becomes superimposed in the second half of gestation, although residua of the columnar pattern persist postnatally, particularly where the cortex bends: at the crowns of gyri and in the depths of sulci. Columnar architecture of the cortical plate in the first half of gestation mostly results from radial migration of neuroblasts, but the Cajal-Retzius neurons and GABAergic neuroblasts from tangential migration regulate a transition to horizontal lamination of the mature cortex. In children and adults, prominent columnar architecture is a feature of many focal cortical dysplasias and is now recognized as a distinctive pattern of focal cortical dysplasias in the new International League Against Epilepsy classification. It also occurs, however, in many genetic syndromes and chromosomopathic conditions, including 22q12 deletions (DiGeorge syndrome), in several primary cerebral malformations, in the contralateral cingulate gyrus in hemimegalencephaly, in cortical tubers of tuberous sclerosis, in the margins of porencephalic cysts resulting from prenatal infarcts, and in some inborn metabolic defects such as methylmalonic acidemia. Synaptophysin demonstrates both radial and horizontal lamination of synaptic layers. Persistent fetal cortical architecture is potentially epileptogenic. We conclude that columnar architecture is a maturational arrest in histogenesis of the neocortical plate and becomes a component of cortical dysplasia in the perinatal period. An initially physiological process thus becomes pathologic by virtue of advancing age, but traces of it persist in normal mature brains. It also occurs in many genetic and inborn metabolic diseases and after acquired ischemic insults of the fetal brain.

High-frequency oscillations, extent of surgical resection, and surgical outcome in drug-resistant focal epilepsy

PURPOSE

Removal of areas generating high-frequency oscillations (HFOs) recorded from the intracerebral electroencephalography (iEEG) of patients with medically intractable epilepsy has been found to be correlated with improved surgical outcome. However, whether differences exist according to the type of epilepsy is largely unknown. We performed a comparative assessment of the impact of removing HFO-generating tissue on surgical outcome between temporal lobe epilepsy (TLE) and extratemporal lobe epilepsy (ETLE). We also assessed the relationship between the extent of surgical resection and surgical outcome.

METHODS

We studied 30 patients with drug-resistant focal epilepsy, 21 with TLE and 9 with ETLE. Two thirds of the patients were included in a previous report and for these, clinical and imaging data were updated and follow-up was extended. All patients underwent iEEG investigations (500 Hz high-pass filter and 2,000 Hz sampling rate), surgical resection, and postoperative magnetic resonance imaging (MRI). HFOs (ripples, 80-250 Hz; fast ripples, >250 Hz) were identified visually on a 5-10 min interictal iEEG sample. HFO rates inside versus outside the seizure-onset zone (SOZ), in resected versus nonresected tissue, and their association with surgical outcome (ILAE classification) were assessed in the entire cohort, and in the TLE and ETLE subgroups. We also tested the correlation of resected brain hippocampal and amygdala volumes (as measured on postoperative MRIs) with surgical outcome.

KEY FINDINGS

HFO rates were significantly higher inside the SOZ than outside in the entire cohort and TLE subgroup, but not in the ETLE subgroup. In all groups, HFO rates did not differ significantly between resected and nonresected tissue. Surgical outcome was better when higher HFO rates were included in the surgical resection in the entire cohort and TLE subgroup, but not in the ETLE subgroup. Resected brain hippocampal and amygdala volumes were not correlated with surgical outcome.

SIGNIFICANCE

In TLE, removal of HFO-generating areas may lead to improved surgical outcome. Less consistent findings emerge from ETLE, but these may be related to sample size limitations of this study. Size of resection, a factor that was ignored and that could have affected results of earlier studies did not influence results.

Is reoperation an option for patients with temporal lobe epilepsy after failure of surgery?

PURPOSE

Epilepsy surgery is the most efficacious therapeutic modality for patients with medically refractory focal epilepsies, but surgical failures remain a challenge to the epilepsy treatment team. The aim of present study was to evaluate the postoperative outcome of patients who underwent reoperation after a failed epilepsy surgery on the temporal lobe.

METHODS

We systematically analyzed the results of comprehensive preoperative evaluations before the first surgery, and before and after reoperation in 17 patients with drug resistant temporal lobe epilepsies.

RESULTS

Overall, 13 of 17 patients (76.5%) improved after reoperation: five patients (29.4%) were completely seizure free after reoperation (median duration 60months, range 12-72); six patients (35.3%) were seizure free at least 12month before observation points (median duration 120.5months, range 35-155) and two patients (11.8%) had a decrease in seizure frequency. Four patients (23.5%) remained unchanged with respect to seizure frequency and severity. There was no correlation between the improvement in seizure outcome after reoperation and other clinical data except of the history of traumatic brain injury (TBI). The patients who had no history of TBI improved after reoperation, compared to patients with TBI (p=0.044). The postoperative seizure outcome of patients with incongruent Video-EEG results before the first surgery (p=0.116) and before reoperation (p=0.622) was not poorer compared to patients with congruent Video-EEG results.

CONCLUSIONS

Reoperation can considerably improve the operative outcome of the first failed epilepsy surgery in patients with drug resistant temporal lobe epilepsies. Epilepsy centres should be encouraged to report the results of failed epilepsy surgeries.

Abdominal auras in patients with mesial temporal sclerosis

To better clarify abdominal auras and their clinical correlates, we enrolled 331 temporal lobe epilepsy patients who received surgical treatment. Detailed descriptions of their auras were obtained before surgery and reconfirmed during postoperative outpatient follow-ups. Pathology revealed mesial temporal sclerosis (MTS) in 256 patients (77.3%) and 75 non-MTS. Of 214 MTS patients with auras, 78 (36.4%) reported abdominal auras (vs. 30.4% in non-MTS, p=0.439): 42 with left-sided seizure onset, and 36 with right-sided seizure onset. Moreover, 49 of the 78 MTS patients had abdominal auras accompanied by rising sensations (vs. 2 of 14 in non-MTS group, p=0.004). The "rising air" was initially described to locate to the epigastric (47.8%) or periumbilical area (45.7%) and mostly reached the chest (40.4%) or remained in the abdominal region (27.1%). An epigastric location of "rising air" favored a left-sided seizure onset, and non-epigastric areas favored right-sided seizure onset (p=0.018). Finally, we found that abdominal auras with or without rising sensations did not predict postoperative seizure outcomes.

Nonrandomness, nonlinear dependence, and nonstationarity of electroencephalographic recordings from epilepsy patients

To derive tests for randomness, nonlinear-independence, and stationarity, we combine surrogates with a nonlinear prediction error, a nonlinear interdependence measure, and linear variability measures, respectively. We apply these tests to intracranial electroencephalographic recordings (EEG) from patients suffering from pharmacoresistant focal-onset epilepsy. These recordings had been performed prior to and independent from our study as part of the epilepsy diagnostics. The clinical purpose of these recordings was to delineate the brain areas to be surgically removed in each individual patient in order to achieve seizure control. This allowed us to define two distinct sets of signals: One set of signals recorded from brain areas where the first ictal EEG signal changes were detected as judged by expert visual inspection ("focal signals") and one set of signals recorded from brain areas that were not involved at seizure onset ("nonfocal signals"). We find more rejections for both the randomness and the nonlinear-independence test for focal versus nonfocal signals. In contrast more rejections of the stationarity test are found for nonfocal signals. Furthermore, while for nonfocal signals the rejection of the stationarity test increases the rejection probability of the randomness and nonlinear-independence test substantially, we find a much weaker influence for the focal signals. In consequence, the contrast between the focal and nonfocal signals obtained from the randomness and nonlinear-independence test is further enhanced when we exclude signals for which the stationarity test is rejected. To study the dependence between the randomness and nonlinear-independence test we include only focal signals for which the stationarity test is not rejected. We show that the rejection of these two tests correlates across signals. The rejection of either test is, however, neither necessary nor sufficient for the rejection of the other test. Thus, our results suggest that EEG signals from epileptogenic brain areas are less random, more nonlinear-dependent, and more stationary compared to signals recorded from nonepileptogenic brain areas. We provide the data, source code, and detailed results in the public domain.

Interrater reliability of Engel, International League Against Epilepsy, and McHugh seizure outcome classifications following vagus nerve stimulator implantation

OBJECT

Interrater reliability as measured by the kappa (κ) statistic is a widely used and valuable tool to measure the robustness of a scoring system. Seizure frequency reduction is a central outcome measure following vagus nerve stimulation (VNS). A specific VNS scoring system has been proposed by McHugh, but its interrater reliability has not been tested. The authors assessed its interrater reliability and compared it with that of the Engel and International League Against Epilepsy (ILAE) systems.

METHODS

Using the Engel, ILAE, and McHugh scoring systems, 3 observers independently rated the medical records of children who had undergone vagus nerve stimulator implantation between January 2001 and April 2011 at the Southampton University Hospital. The interrater agreements were then calculated using the κ statistic.

RESULTS

Interrater reliability for the McHugh scale (κ0.693) was very good and was superior to those of the Engel (κ0.464) and ILAE (κ0.491) systems for assessing outcome in patients undergoing VNS.

CONCLUSIONS

The authors recommend considering the McHugh scoring system when assessing outcomes following VNS.

Seizure outcome, functional outcome, and quality of life after hemispherectomy in adults

BACKGROUND

Functional hemispherectomy is a well-established method in childhood epilepsy surgery with only a few reports on its application in adults.

METHODS

We report on 27 patients (median age 30 years, range 19-55) with a follow-up of more than 1 year (median 124 months, range 13-234). Etiology was developmental in two (one schizencephaly, one hemimegalencephaly), acquired in 21 (two hemiatrophy, 17 porencephaly, two postencephalitic), and progressive in four (Rasmussen's encephalitis).

RESULTS

At last available follow-up, 22 patients were seizure free (81 % ILAE class 1), one had auras (4 % ILAE class 2), one had no more than three seizures per year (4 % ILAE class 3). Thirty-seven percent were without antiepileptic drugs. Seventeen patients of 20 responding patients stated improved quality of life after surgery, one patient reported deterioration, and two patients reported no difference. Additionally, a self-rated postoperative functional status and changes compared to the pre-operative status was assessed. Six patients improved in gait, ten remained unchanged, and four deteriorated. Three patients improved in speech, none deteriorated. Hand function got worse five times, and in 15 cases remained unchanged. There was no mortality, one bone flap infection, and one subdural hematoma. Hydrocephalus was seen in three cases (12 %).

CONCLUSIONS

It is possible to achieve good seizure outcome results despite long-standing epilepsy across a variety of etiologies, comparable to epilepsy surgery in pediatric patients. Adult patients do not have to expect more problems with new deficits, appear to cope quite well, and mostly profit from surgery in several quality of life domains.

Novel pathological abnormalities of deep brain structures including dysplastic neurons in anterior striatum associated with focal cortical dysplasia in epilepsy

OBJECT

Some patients are not seizure free even after epileptogenic cortical resection. The authors recently described a case of frontal lobe epilepsy cured after the resection of periventricular white matter and striatum, in which dysplastic neurons were revealed. The authors attempted to confirm similar cases.

METHODS

They reviewed the records of 8 children with frontal lobe epilepsy who had daily (7) or monthly (1) seizures and underwent resections including deep brain structures.

RESULTS

Five patients underwent multiple resections. Neuroimaging of the deep structures showed the transmantle sign in 3 patients, ictal hyperperfusion in 6, reduced iomazenil uptake in 2, and spike dipole clustering in 6. All patients became seizure free postoperatively. Focal cortical dysplasia of various types was diagnosed in all patients. Dysmorphic neurons were found in the cortex and subcortical white matter of 5 patients. The striatum was verified in 3 patients in whom dysmorphic neurons were scattered. In the periventricular white matter, prominent astrocytosis was evident in all cases.

CONCLUSIONS

Pathological abnormalities such as dysmorphic neurons and astrocytosis in deep brain structures would play a key role in epileptogenesis.

Seizure outcome 1 year after temporal lobe epilepsy: an analysis of MR volumetric and clinical parameters

BACKGROUND

The aim of this work was to determine predictors that may contribute to surgical success or failure. Relevant pre- and postoperative baseline data were analyzed, and temporal structures underwent a volumetric analysis.

METHODS

A total of 207 patients (107 female) underwent complete evaluation for epilepsy surgery. Prospectively collected data used for this analysis included the clinical and demographic data. Classic prognostic factors (e.g., gender, age at operation, age at epilepsy manifestation, duration of epilepsy, education, side of pathology, intracranial EEG recordings, secondarily generalized tonic-clonic seizures, etiological factors, histology) and a volumetric analysis of 12 temporal lobe subregions were used in a regression analysis to identify possible prognostic factors in surgery for TLE. Primary outcome measure was seizure freedom at 1 year and during the full first year expressed as class I in the ILAE outcome scale.

RESULTS

In the univariate analysis, we identified one negative predictor for a less favorable seizure outcome: intracranial EEG recordings (p = 0.010), hippocampal sclerosis as histological finding trended toward statistical significance (p = 0.054). No statistical outcome significance was found for preoperative temporal lobe compartment volume loss or postoperative lateral atrophy after mesial resection.

CONCLUSIONS

Necessity for intracranial EEG recording is an independent factor of not optimal seizure control in the 1-year follow-up. Preoperative temporal lobe volume differences including smaller mesial subcompartments did not correlate with poorer seizure outcome.

Epilepsy surgery: how accurate are multidisciplinary teams in predicting outcome?

BACKGROUND

Since epilepsy surgery is an elective procedure, patients need to weigh the risks of the procedure against the likely outcome if they are to make an informed decision to proceed. The aim of this study was to examine the accuracy of multidisciplinary team predictions of postoperative outcome in epilepsy surgery candidates.

METHODS

An experienced multidisciplinary team provided preoperative predictions of postoperative outcome in 94 temporal lobe epilepsy patients who subsequently proceeded to surgery and were followed up one year later.

RESULTS

Team predictions of postoperative outcome were generally accurate for groups of patients judged to have a 30%, 40%, 50% or 60% chance of becoming seizure free. Team estimates of odds tended to regress towards the mean. Logistic regression analyses were more accurate than the team estimates in identifying patients with a very good (>70%) or very poor (<20%) chance of complete seizure freedom. Non localising scalp EEG, necessitating the need for an invasive EEG study prior to surgery was a significant predictor of poor postoperative outcome in this series.

CONCLUSIONS

Probabilities based on logistic regression models may augment and improve the accuracy of clinical estimates of postoperative outcome in patients with a very good or very poor chance of being rendered seizure free by surgery, by counteracting the tendency of regression towards the mean in team decision making.

Seizure outcome and complications following hypothalamic hamartoma treatment in adults: endoscopic, open, and Gamma Knife procedures

OBJECT

This study aimed at identifying outcomes with respect to seizures, morbidity, and mortality in adult patients undergoing resective or Gamma Knife surgery (GKS) to treat intractable epilepsy associated with hypothalamic hamartoma (HH).

METHODS

Adult patients undergoing surgical treatment for HH-related epilepsy were prospectively monitored at a single center for complications and seizure outcome by using a proprietary database. Preintervention and postintervention data for patients 18 years of age and older, and with at least 1 year of follow-up, were analyzed, with specific attention to seizure control, complications, hormonal status, and death.

RESULTS

Forty adult patients were found in the database (21 were women). The median HH volume was 0.54 cm(3). In 70% of patients, it was located inside the third ventricle, attached unilaterally and vertically to the hypothalamus (Delalande Type II). Most patients (26) underwent an endoscopic resection, 10 patients had a transcallosal or other type of open (pterional or orbitozygomatic) resection, and 4 patients chose GKS. Twenty-nine percent became seizure free in the long term, and overall a majority of patients (55%) reported at least > 90% seizure improvement. Only 3 patients were ultimately able to discontinue anticonvulsants, whereas most patients were taking an average of 2 antiepileptic drugs pre- and postoperatively. The only factor significantly correlated with seizure-free outcome was the absence of mental retardation. The HH volume, HH type, and amount of resection or disconnection were not correlated to seizure freedom. A total of 4 patients (10%) died, 2 immediately after surgery and 2 later. All of them had undergone a resection, as opposed to GKS, and still had seizures. Postoperatively, persistent neurological deficits were seen in 1 patient; 34% of patients had mild hormonal problems; and 59% experienced weight gain of at least 6.8 kg (average gain 12.7 kg).

CONCLUSIONS

Surgical or GKS procedures in adults with HH provided seizure freedom in one-third of patients. The only significant favorable prognostic factor was the absence of mental retardation. The overall mortality rate was high, at 10%. Other important morbidities were persistent hormonal disturbances and weight gain.

A longitudinal study of psychological features in patients before and two years after epilepsy surgery

This study aimed at investigating psychological features before and two years after epilepsy surgery. Fifty patients, 39 with temporal lobe epilepsy (TLE) and 11 with frontal lobe epilepsy (FLE), were assessed at baseline and two years postoperatively with the Karolinska Scales of Personality (KSP). Baseline group level outcome was normal while individual level analyses delineated some mild to moderate degrees of psychological problems exceeding the normal range in subsets of patients. Features of hostility characterized half of the FLE and one-fourth of the TLE patients. Above 1/3 in each group had dependency features. About 1/3 of the TLE patients suffered from psychasthenia. In conclusion, even though group levels were normal, several patients had psychological problems. The main longitudinal result was that the personality features were stable and did not change after epilepsy surgery.

A meta-analysis of predictors of seizure freedom in the surgical management of focal cortical dysplasia

Object

Focal cortical dysplasia (FCD) is one of the most common causes of medically refractory epilepsy leading to surgery. However, seizure control outcomes reported in isolated surgical series are highly variable. As a result, it is not clear which variables are most crucial in predicting seizure freedom following surgery for FCD. The authors' aim was to determine the prognostic factors for seizure control in FCD by performing a meta-analysis of the published literature.

Methods

A MEDLINE search of the published literature yielded 37 studies that met inclusion and exclusion criteria. Seven potential prognostic variables were determined from these studies and were dichotomized for analysis. For each variable, individual studies were weighted by inverse variance and combined to generate an odds ratio favoring seizure freedom. The methods complied with a standardized meta-analysis reporting protocol.

Results

Two thousand fourteen patients were included in the analysis. The overall rate of seizure freedom (Engel Class I) among patients undergoing surgery for FCD in the cohort of studies was 55.8% ± 16.2%. Partial seizures, a temporal location, detection with MRI, and a Type II Palmini histological classification were associated with higher rates of postoperative seizure control. As a treatment-related factor, complete resection of the anatomical or electrographic abnormality was the most important predictor overall of seizure freedom. Neither age nor electroencephalographic localization of the ictal onset significantly affected seizure freedom after surgery.

Conclusions

Using a large population cohort pooled from the published literature, an analysis identified important factors that are prognostic in patients with epilepsy due to FCD. The most important of these factors—diagnostic imaging and resection—provide modalities through which improvements in the impact of FCD can be effected.

Imaging language networks before and after anterior temporal lobe resection: results of a longitudinal fMRI study

Summary

Purpose: 

Anterior temporal lobe resection (ATLR) controls seizures in up to 70% of patients with intractable temporal lobe epilepsy (TLE) but, in the language dominant hemisphere, may impair language function, particularly naming. Functional reorganization can occur within the ipsilateral and contralateral hemispheres. We investigated reorganization of language in left-hemisphere–dominant patients before and after ATLR; whether preoperative functional magnetic resonance imaging (fMRI) predicts postoperative naming decline; and efficiency of postoperative language networks.

Methods: 

We studied 44 patients with TLE due to unilateral hippocampal sclerosis (24 left) on a 3T GE-MRI scanner. All subjects performed language fMRI and neuropsychological testing preoperatively and again 4 months after left or right ATLR.

Key Findings: 

Postoperatively, individuals with left TLE had greater bilateral middle/inferior frontal fMRI activation and stronger functional connectivity from the left inferior/middle frontal gyri to the contralateral frontal lobe than preoperatively, and this was not observed in individuals with right TLE. Preoperatively, in left and right TLE, better naming correlated with greater preoperative left hippocampal and left frontal activation for verbal fluency (VF). In left TLE, stronger preoperative left middle frontal activation for VF was predictive of greater decline in naming after ATLR. Postoperatively, in left TLE with clinically significant naming decline, greater right middle frontal VF activation correlated with better postoperative naming. In patients without postoperative naming decline, better naming correlated with greater activation in the remaining left posterior hippocampus. In right TLE, naming ability correlated with left hippocampal and left and right frontal VF activation postoperatively.

Significance: 

In left TLE, early postoperative reorganization to the contralateral frontal lobe suggests multiple systems support language function. Postoperatively, ipsilateral recruitment involving the posterior hippocampal remnant is important for maintaining language, and reorganization to the contralateral hemisphere is less effective. Preoperative left middle frontal activation for VF was predictive of naming decline in left TLE after ATLR.

Intractable epilepsy in paralimbic Word Health Organization Grade II gliomas: should the hippocampus be resected when not invaded by the tumor?

OBJECT

Beyond its oncological benefit, surgery could improve seizure control in paralimbic frontotemporoinsular or temporoinsular WHO Grade II gliomas generating intractable seizures. However, no studies have examined the impact of hippocampal resection on chronic epilepsy when the hippocampus is not invaded by Grade II gliomas. Here, the authors compared the epileptological outcomes and return to work in 2 groups of patients who underwent surgery with or without hippocampectomy for paralimbic Grade II gliomas eliciting intractable epilepsy despite no tumoral involvement of the hippocampus.

METHODS

Surgery was performed in 15 consecutive patients who were unable to work (median Karnofsky Performance Scale [KPS] Score 70) because of refractory epilepsy due to paralimbic Grade II gliomas that were not invading the hippocampus. In Group A (8 patients), the hippocampus was preserved. In Group B (7 patients), glioma removal was associated with hippocampectomy.

RESULTS

No patient died or suffered a permanent deficit after surgery. Postoperatively, in Group A, no patients were seizure free (4 patients were in Engel Class II and 4 were in Class III). In Group B, all 7 patients were seizure free (Class I) (p = 0.02). Only 62.5% of patients returned to work in Group A, whereas all patients are working full time in Group B. The postsurgical median KPS score was 85 in Group A, that is, not significantly improved in comparison with the preoperative score, while the postsurgical median KPS was 95 in Group B, that is, significantly improved in comparison with the preoperative score (p = 0.03).

CONCLUSIONS

The authors' data support, for the first time, the significant impact of hippocampectomy in patients with intractable epilepsy generated by a paralimbic Grade II glioma, even if it does not invade the hippocampus. Hippocampal resection allowed seizure control in all patients, with an improvement in KPS scores, since all patients resumed their social and professional activities. Thus, the authors suggest performing a resection of the nontumoral hippocampus in addition to resection of the tumor in patients with refractory epilepsy due to paralimbic Grade II gliomas.

Ictal high-gamma oscillation (60-99 Hz) in intracranial electroencephalography and postoperative seizure outcome in neocortical epilepsy

OBJECTIVE

High-gamma oscillations (HGOs) (60-99 Hz) have been suggested to correlate with seizure onset zones and seizure outcomes. We investigated the correlation between the extent of removal of ictal HGO generating areas and postoperative seizure outcome in neocortical epilepsy (NE).

METHODS

Twenty three patients with medically intractable NE underwent chronic intracranial electroencephalography (iEEG) using subdural electrodes. Ictal HGOs and superimposed undersampled ripples within ±3 s of video-iEEG ictal onset were extracted by wavelet clustering and thresholding. Cluster epileptogenicity indices (CEIs) were calculated. The temporal analysis window was locked to the timing of the maximum CEI wavecluster. Root mean square amplitudes, cross-correlation synchronies and the local focus indices within the temporal window were calculated.

RESULTS

Percentages of resected maximum CEI waveclusters and HGO zones with high standardised amplitudes (>3), high cross-correlation synchronies (>0.9) and high local focus indices (>2) were significantly higher in the seizure-free group compared to the not seizure-free group (p=0.036, p=0.018, and p=0.026, respectively).

CONCLUSIONS

The automatic quantitative ictal HGO analysis may be effective in delineating the epileptogenic zone.

SIGNIFICANCE

HGO analysis may be helpful for improving post-resection seizure outcome in NE in the future.

Epileptic networks in focal cortical dysplasia revealed using electroencephalography-functional magnetic resonance imaging

OBJECTIVE

Surgical treatment of focal epilepsy in patients with focal cortical dysplasia (FCD) is most successful if all epileptogenic tissue is resected. This may not be evident on structural magnetic resonance imaging (MRI), so intracranial electroencephalography (icEEG) is needed to delineate the seizure onset zone (SOZ). EEG-functional MRI (fMRI) can reveal interictal discharge (IED)-related hemodynamic changes in the irritative zone (IZ). We assessed the value of EEG-fMRI in patients with FCD-associated focal epilepsy by examining the relationship between IED-related hemodynamic changes, icEEG findings, and postoperative outcome.

METHODS

Twenty-three patients with FCD-associated focal epilepsy undergoing presurgical evaluation including icEEG underwent simultaneous EEG-fMRI at 3T. IED-related hemodynamic changes were modeled, and results were overlaid on coregistered T1-weighted MRI scans fused with computed tomography scans showing the intracranial electrodes. IED-related hemodynamic changes were compared with the SOZ on icEEG and postoperative outcome at 1 year.

RESULTS

Twelve of 23 patients had IEDs during recording, and 11 of 12 had significant IED-related hemodynamic changes. The fMRI results were concordant with the SOZ in 5 of 11 patients, all of whom had a solitary SOZ on icEEG. Four of 5 had >50% reduction in seizure frequency following resective surgery. The remaining 6 of 11 patients had widespread or discordant regions of IED-related fMRI signal change. Five of 6 had either a poor surgical outcome (<50% reduction in seizure frequency) or widespread SOZ precluding surgery.

INTERPRETATION

Comparison of EEG-fMRI with icEEG suggests that EEG-fMRI may provide useful additional information about the SOZ in FCD. Widely distributed discordant regions of IED-related hemodynamic change appear to be associated with a widespread SOZ and poor postsurgical outcome.

Impact of epilepsy surgery on seizure control and quality of life: a 26-year follow-up study

PURPOSE

The short-term efficacy and safety of epilepsy surgery relative to medical therapy has been established, but it remains underutilized. There is a lack of data regarding the long-term seizure-control rates and quality of life outcomes after epilepsy surgery. This study represents the longest follow-up study to date, with a mean follow-up duration of 26 years.

METHODS

We studied the seizure and health-related quality of life outcomes of patients who underwent epilepsy surgery by Dr. Sidney Goldring from 1967 to 1990. Retrospective clinical chart reviews gathered perioperative data and surveys obtained follow-up data. Seizure outcome was evaluated using the Engel classification system.

KEY FINDINGS

Of 361 patients, 117 (32.4%) completed follow-up interviews. Fifty-six patients (48%) were Engel class I. Mean overall Quality of Life in Epilepsy (QOLIE-31) questionnaire score for the cohort was 68.2 ± 16. Eighty percent of patients reported their overall quality of life now as being better than before surgery. Seizure freedom was associated with better quality of life. We did not observe a statistically significant association between postoperative complications and long-term outcome. Patients who underwent temporal lobe resection achieved better seizure outcomes than those who underwent other types of procedures. Astatic seizures and bilateral surgery were associated with a worse Engel class outcome.

SIGNIFICANCE

Our study demonstrates that the beneficial effects of epilepsy surgery are sustained over decades, and that these beneficial effects are correlated with an improved quality of life. The confirmation of its durability makes us optimistic that the outcomes from modern epilepsy surgery will be even better and that our present enthusiasm for this treatment modality is not misplaced.

Histopathology of cortex and white matter in pediatric epileptic spasms: comparison with those of partial seizures

Epileptic spasms in older children have increasingly been recognized as a distinct seizure type and subset of these patients are considered for surgical resection. This study compares histopathology and magnetic resonance imaging (MRI), especially focusing the difference between the cortical grey matter and the subcortical white matter to understand the extensive epileptic brain in patients with epileptic spasms. We examined 22 patients consisting of 11 patients with epileptic spasms and 11 with partial seizures. Scalp video electroencephalography (EEG) showed interictal generalized epileptiform discharges (9 patients with epileptic spasms vs. 1 with partial seizures) and ictal generalized epileptiform discharges (10 vs. 3). We found MRI abnormalities in a single lobe (6 vs. 7) and multiple lobes (2 vs. 1). Surgical resections were performed across multiple lobes (9 vs. 2), comparing within a single lobe (2 vs. 9), (p<0.001). Histopathology showed abnormal cortical organizations as FCD (2 vs. 5) and microdysgenesis (4 vs. 4), normal (4 vs. 1). Two patients with epileptic spasms showed hyaline proteoplasmic astrocytopathy. There were heterotopic neurons (10 vs. 10), cluster of oligodendroglia (8 vs. 7), balloon cells (2 vs. 5) and blurred myelination (1 vs. 4), in the white matter. Seizure-free outcomes were seen in seven patients with epileptic spasms (64%) and four with partial seizures (36%). The multilobar epileptogenic zones existed in patients with epileptic spasms, compared with the focal epileptogenic zone in patients with partial seizures. There was no difference of MRI and histopathology findings in cortex and subcortical white matter between two groups.

Neuropsychological function in patients who have had epilepsy surgery: a long-term follow-up

We examined the relationship between seizure outcomes and long-term changes in memory and intellectual function in 70 patients who had undergone temporal lobe resection for medically intractable epilepsy. Patients were assessed on four occasions: preoperatively (T1), 3 months postoperatively (T2), 1 year postoperatively (T3), and more than 5 years postoperatively (T4). The majority of patients had stable memory function across the assessments. However, many were functioning below the 15th percentile on the test norms preoperatively, with little capacity for further decline. All patients who demonstrated a progressive decline in verbal or visual learning were female and continued to experience seizures postoperatively. Progressive postoperative declines in memory function are associated with poor postoperative seizure control. These patterns can be obscured in group analyses that do not take into account baseline levels of function. Neuropsychological scores must be set in the context of the norms of the test and the associated capacity for further significant change over time to maximize the clinical relevance of long-term surgical follow-up studies.

The role of magnetoencephalography in children undergoing hemispherectomy

OBJECT

Hemispherectomy is an established neurosurgical procedure for medication-resistant epilepsy in children. Despite the effectiveness of this technique, there are patients who do not achieve an optimum outcome after surgery; possible causes of suboptimal results include the presence of bilateral independent epileptogenic foci. Magnetoencephalography (MEG) is an emerging tool that has been found to be useful in the management of lesional and nonlesional epilepsy. The authors analyzed the relative contribution of MEG in patient selection for hemispherectomy.

METHODS

The medical records of children undergoing hemispherectomy at the Hospital for Sick Children were reviewed. Those patients who underwent MEG as part of the presurgical evaluation were selected.

RESULTS

Thirteen patients were included in the study. Nine patients were boys. The mean age at the time of surgery was 66 months (range 10-149 months). Seizure etiology was Rasmussen encephalitis in 6 patients, hemimegalencephaly in 2 patients, and cortical dysplasia in 4 patients. In 8 patients, video-EEG and MEG results were consistent to localize the primary epileptogenic hemisphere. In 2 patients, video-EEG lateralized the ictal onset, but MEG showed bilateral spikes. Two patients had bilateral video-EEG and MEG spikes. Engel Class I, II, and IV outcomes were seen in 10, 2, and 1 patients, respectively. In 2 of the patients who had an outcome other than Engel Class I, the MEG clusters were concentrated in the disconnected hemisphere. The third patient had bilateral clusters and potentially independent epileptogenic foci from bilateral cortical dysplasia.

CONCLUSIONS

The presence of unilateral MEG spike waves correlated with good outcomes following hemispherectomy. In some cases, MEG provides information that differs from that obtained from video-EEG and conventional MR imaging studies. Further studies with a greater number of patients are needed to assess the role of MEG in the preoperative assessment of candidates for hemispherectomy.

The long-term outcome of adult epilepsy surgery, patterns of seizure remission, and relapse: a cohort study

BACKGROUND

Surgery is increasingly used as treatment for refractory focal epilepsy; however, few rigorous reports of long-term outcome exist. We did this study to identify long-term outcome of epilepsy surgery in adults by establishing patterns of seizure remission and relapse after surgery.

METHODS

We report long-term outcome of surgery for epilepsy in 615 adults (497 anterior temporal resections, 40 temporal lesionectomies, 40 extratemporal lesionectomies, 20 extratemporal resections, 11 hemispherectomies, and seven palliative procedures [corpus callosotomy, subpial transection]), with prospective annual follow-up for a median of 8 years (range 1-19). We used Kaplan-Meier survival analysis to estimate time to first seizure, and investigated patterns of seizure outcome.

FINDINGS

We used survival methods to estimate that 52% (95% CI 48-56) of patients remained seizure free (apart from simple partial seizures [SPS]) at 5 years after surgery, and 47% (42-51) at 10 years. Patients who had extratemporal resections were more likely to have seizure recurrence than were those who had anterior temporal resections (hazard ratio [HR] 2·0, 1·1-3·6; p=0·02); whereas for those having lesionectomies, no difference from anterior lobe resection was recorded. Those with SPS in the first 2 years after temporal lobe surgery had a greater chance of subsequent seizures with impaired awareness than did those with no SPS (2·4, 1·5-3·9). Relapse was less likely the longer a person was seizure free and, conversely, remission was less likely the longer seizures continued. In 18 (19%) of 93 people, late remission was associated with introduction of a previously untried antiepileptic drug. 104 of 365 (28%) seizure-free individuals had discontinued drugs at latest follow-up.

INTERPRETATION

Neurosurgical treatment is appealing for selected people with refractory focal epilepsy. Our data provide realistic expectations and indicate the scope for further improvements in presurgical assessment and surgical treatment of people with chronic epilepsy.

FUNDING

UK Department of Health National Institute for Health Research (NIHR) Biomedical Research Centres funding scheme, Epilepsy Society, Dr Marvin Weil Epilepsy Research Fund.

Surgical decision making in temporal lobe epilepsy: a comparison of [(18)F]FDG-PET, MRI, and EEG

OBJECTIVES

The goals of this work were (1) to determine the effect of [(18)F]fluorodeoxyglucose positron emission tomography (FDG-PET), MRI, and EEG on the decision to perform temporal lobe epilepsy (TLE) surgery, and (2) to determine if FDG-PET, MRI, or EEG predicts surgical outcome.

METHODS

All PET scans ordered (2000-2010) for epilepsy or seizures were tabulated. Medical records were investigated to determine eligibility and collect data. Statistical analysis included odds ratios, κ statistics, univariate analysis, and logistic regression.

RESULTS

Of the 186 patients who underwent FDG-PET, 124 had TLE, 50 were surgical candidates, and 34 had surgery with post-operative follow-up. Median length of follow-up was 24 months. MRI, FDG-PET, and EEG were significant predictors of surgical candidacy (P<0.001) with odds ratios of 42.8, 20.4, and 6.3, respectively. FDG-PET was the only significant predictor of postoperative outcome (P<0.01).

CONCLUSION

MRI showed a trend toward having the most influence on surgical candidacy, but only FDG-PET predicted surgical outcome.

Very good inter-rater reliability of Engel and ILAE epilepsy surgery outcome classifications in a series of 76 patients

The inter-rater reliability, expressed as kappa score, k, of the Engel and International League Against Epilepsy (ILAE) classifications of epilepsy surgery seizure outcome has not previously been evaluated. In a consecutive series of 76 patients (40 male; 25 children), 75 undergoing resective and 1 disconnective surgery at a mean age of 27.5 years (13 months-62 years), one observer classified 88% (n=67) and a second observer classified 87% (n=66) of patients as either Engel I or II (free from or rare disabling seizures) after a median follow up of 36 months (range 12-92 months); comparably, both observers classified 84% (n=64) as ILAE 1-3. Correlation for Engel versus ILAE for observer 1 was 0.933 (p<.0005) and for observer 2 was 0.931 (p<.0005). Both ILAE (k 0.81, 95% confidence intervals 0.69, 0.91) and Engel (k 0.77, 95% CI 0.65, 0.87) classifications have very acceptable inter-rater reliability as well as significant correlation.

Current challenges in the practice of epilepsy surgery

The accurate prediction of individual outcomes after epilepsy surgery represents a key challenge facing clinicians. It requires a precise understanding of surgical candidacy and the optimal timing of surgery to maximize a range of outcomes, including medical, psychosocial, cognitive, and psychiatric outcomes. We promote careful consideration of how epilepsy has affected an individual's developmental trajectory as key to constructing more differentiated profiles of postsurgical risk or resilience across multiple outcome measures. This life span approach conceives surgery as a crucial "turning point" in an individual's development from which varied outcome trajectories may follow. This helps clinicians understand the expectations patients and families bring to surgery, and emphasizes the interplay of factors that determine a patient's outcome. It also promotes comprehensive, longitudinal assessment of outcome using data analytical techniques that capture individual differences and identify subgroups with similar trajectories. An ongoing challenge facing clinicians is the development of an outcome classification system that incorporates outcomes other than seizures. We illustrate two emerging areas of research shaping how we define surgical candidacy and predict outcome: (1) using cortico-cortical evoked potentials to identify pathways of seizure propagation and cortico-cortical networks mediating cortical functions, and (2) predicting postoperative depression using a model that incorporates psychosocial and neurobiological factors. The latter research points to the importance of routine follow-up and postoperative psychosocial rehabilitation, particularly in patients deemed at "high risk" for poor outcomes so that early treatment interventions can be implemented. Significantly more research is needed to characterize those patients with poor outcomes who may require re-surgery.

Genomic microdeletions associated with epilepsy: not a contraindication to resective surgery

PURPOSE

Several recent reports of genomic microdeletions in epilepsy will generate further research; discovery of more microdeletions and other important classes of variants may follow. Detection of such genetic abnormalities in patients being evaluated for surgical treatment might raise concern that a genetic defect, possibly widely expressed in the brain, will affect surgical outcome.

METHODS

A reevaluation was undertaken of clinical presurgical data, histopathology of surgical specimen, and postsurgical outcome in patients with mesial temporal lobe epilepsy (MTLE) who have had surgical treatment for their drug-resistant seizures, and who have been found to have particular genomic microdeletions.

KEY FINDINGS

Three thousand eight hundred twelve patients with epilepsy were genotyped and had a genome-wide screen to identify copy number variation. Ten patients with MTLE, who had resective epilepsy surgery, were found to have 16p13.11 microdeletions or other microdeletions >1 Mb. On histopathology, eight had classical hippocampal sclerosis (HS), one had nonspecific findings, and one had a hamartoma. Median postsurgical follow-up time was 48 months (range 10-156 months). All patients with HS were seizure-free after surgery, International League Against Epilepsy (ILAE) outcome class 1, at last follow-up; the patient with nonspecific pathology had recurrence of infrequent seizures after 7 years of seizure freedom. The patient with a hamartoma never became seizure-free.

SIGNIFICANCE

  Large microdeletions can be found in patients with "typical" MTLE. In this small series, patients with MTLE who meet criteria for resective surgery and harbor large microdeletions, at least those we have detected, can have a good postsurgical outcome. Our findings add to the spectrum of causal heterogeneity of MTLE + HS.

Response assessment in neuro-oncology (a report of the RANO group): assessment of outcome in trials of diffuse low-grade gliomas

Although low-grade gliomas (LGG) have a less aggressive course than do high-grade gliomas, the outcome of these tumours is ultimately fatal in most patients. Both the tumour and its treatment can cause disabling morbidity, particularly of cognitive functions. Because many patients present with seizures only, with no other signs and symptoms, maintenance of quality of life and function constitutes a particular challenge in LGG. The slow growth pattern of most LGG, and the rare radiological true responses despite a favourable clinical response to treatment, interferes with the use of progression-free survival as the primary endpoint in trials. Overall survival as an endpoint brings logistical challenges, and is sensitive to other non-investigational salvage therapies. Clinical trials for LGG need to consider other measures of patient benefit such as cognition, symptom burden, and seizure activity, to establish whether improved survival is reflected in prolonged wellbeing. This Review investigates clinical and imaging endpoints in trials of LGG, and provides response assessment in neuro-oncology (RANO) criteria for non-enhancing tumours. Additionally, other measures for patients with brain tumours that assess outcome are described. Similar considerations are relevant for trials of high-grade gliomas, although for these tumours survival is shorter and survival endpoints generally have more value than they do for LGG.

Management and long-term outcome in patients presenting with ictal asystole or bradycardia

PURPOSE

Ictal asystole (IA) and ictal bradycardia (IB) are rare autonomic symptoms during epileptic seizures and may be potentially life-threatening. Guidelines for the care of these patients are missing. The aim of this multicenter study was to evaluate the management and long-term outcome in patients with IA and IB.

PATIENTS AND METHODS

All patients with IA and IB were included from four epilepsy centers (Bielefeld, Kork, Marburg, and Zürich) from 2002 until 2009. Using a standardized assessment form, clinical data, treatment decisions, and outcomes were extracted from patient charts and simultaneous electroencephalography/electrocardiography (EEG/ECG) recordings.

KEY FINDINGS

Seizures with IA or IB were identified in 16 patients. In all patients an associated temporal seizure pattern was recorded and in 15 patients, sudden falls, fainting, or trauma was previously reported or recorded during the monitoring. In three patients (18.8%) diagnosis of focal epilepsy was newly established and anticonvulsive treatment was initiated. Two patients with refractory epilepsy underwent epilepsy surgery. In seven patients (43.8%) a cardiac pacemaker was implanted. In 14 of 16 treated patients, seizure freedom (n = 5) or absence of sudden falls, fainting, or trauma (n = 9) could be achieved. Two patients denied epilepsy surgery as well as a pacemaker and continue to have frequent falls and trauma.

SIGNIFICANCE

Our study demonstrates that epilepsy surgery and antiepileptic drugs may lead to sustained freedom of seizures as well as ictal syncope. In drug-resistant patients not suitable for epilepsy surgery, implantation of a cardiac pacemaker may prevent sudden falls as well as trauma. Based on our results and previously reported cases we propose a treatment algorithm.

Reoperation after selective amygdalohippocampectomy: an MRI analysis of the extent of temporomesial resection in ten cases

BACKGROUND

Selective amygdalohippocampectomy (SAHE) yields 60-80% of patients with medically refractory mesial temporal lobe epilepsy seizure-free and seems to be equally effective compared to the more extended temporal lobe resections. The resection of the entire entorhinal cortex (EC) is of crucial importance to warrant complete seizure control for those patients. Thus, evidence of residual EC could be a predictor of a potentially successful reoperation in patients with recurrent seizures after SAHE. We performed an analysis of preoperative and postoperative magnetic resonance imaging (MRI) in patients who underwent a reoperation after an unsuccessful transsylvian SAHE to assess the presence of residual EC before reoperation and to determine whether certain anatomical variants may dispose patients to incomplete resection of EC.

MATERIALS AND METHODS

Ten patients who underwent reoperation after SAHE for the recurrence of medically refractory seizures were studied. MRI after SAHE was assessed for the presence of residual EC using T2-weighted and inversion recovery sequences perpendicularly to the main axis of the hippocampus. The results were compared with a control group of ten patients who became seizure-free after SAHE. In the nine patients of the study group, the sulcal anatomy of the basal temporal lobe was graphically outlined and analysed on MRI scans performed before SAHE to characterise the sulcal boundaries of the EC.

FINDINGS

Residual EC was found in nine of ten patients and was absent in the control group. After reoperation (median follow-up of 36.5 months), eight out of ten patients were completely seizure-free. In seven out of nine patients, a discontinuous course of the lateral sulcal boundaries of the EC was determined.

CONCLUSIONS

Careful analysis of MRI verified residual mesiotemporal structures in the majority of patients who became seizure-free after reoperation. Certain temporobasal sulcal patterns might dispose for a higher risk of incomplete resection of the EC. The study confirms that reoperation is an effective treatment modality for patients with recurrent seizures after transsylvian SAHE.

Cerebral cavernous malformations and intractable epilepsy: the limited usefulness of current literature

BACKGROUND

Cerebral cavernous malformations (CCM) are known to be highly epileptogenic lesions. A number of studies on CCM surgery deal with CCM-associated seizures and/or epilepsy. In order to counsel patients with CCM-associated epilepsy, clear results from such studies would be highly useful. This study reviews the current literature with the aim to assess its usefulness for presurgical decision-making with emphasis on differentiating outcomes in different epilepsy types.

METHODS

A systematic Medline search identified 27 studies between 1991 and 2009 through the keywords "cavernomas, cavernous, hemangioma, AND epilepsy, AND surgery". They were analysed with regard to clarity of definition of epilepsy subtypes, precision of definition of drug-resistant epilepsy, information on surgical procedure and presurgical workup, seizure outcome and length of follow-up.

RESULTS

Twenty studies included only surgically treated patients. Three types of epilepsy were defined: drug-resistant epilepsy, epilepsy or single/sporadic seizures. In 12 of 27 studies, at least one of these categories remained unclear. The classic definition of drug-resistant epilepsy was not used in the vast majority of studies, with many groups using their own definition. In 30%, the surgical procedure was not described precisely, although 52% of studies used a differentiated preoperative evaluation. Seizure outcome was described using a widely accepted classification in only 48% of series, and in over half of the studies outcome results contained cases with insufficient length of follow-up.

CONCLUSIONS

A large proportion of recent studies on surgery for CCM-associated epilepsy are not using criteria and definitions for the classification of epilepsy and outcome that are commonly used by epileptologists or epilepsy surgeons. This results in the limited usefulness of a large part of the literature for the purpose of preoperative counselling a patient with CCM-associated epilepsy.

Graph analysis of epileptogenic networks in human partial epilepsy

PURPOSE

The current gold standard for the localization of the cortical regions responsible for the initiation and propagation of the ictal activity is through the use of invasive electrocorticography (ECoG). This method is utilized to guide surgical intervention in cases of medically intractable epilepsy by identifying the location and extent of the epileptogenic focus. Recent studies have proposed mechanisms in which the activity of epileptogenic cortical networks, rather than discrete focal sources, contributes to the generation of the ictal state. If true, selective modulation of key network components could be employed for the prevention and termination of the ictal state.

METHODS

Here, we have applied graph theory methods as a means to identify critical network nodes in cortical networks during both ictal and interictal states. ECoG recordings were obtained from a cohort of 25 patients undergoing presurgical monitoring for the treatment of intractable epilepsy at the Mayo Clinic (Rochester, MN, U.S.A.).

KEY FINDINGS

One graph measure, the betweenness centrality, was found to correlate with the location of the resected cortical regions in patients who were seizure-free following surgical intervention. Furthermore, these network interactions were also observed during random nonictal periods as well as during interictal spike activity. These network characteristics were found to be frequency dependent, with high frequency gamma band activity most closely correlated with improved postsurgical outcome as has been reported in previous literature.

SIGNIFICANCE

These findings could lead to improved understanding of epileptogenesis. In addition, this theoretically allows for more targeted therapeutic interventions through the selected modulation or disruption of these epileptogenic networks.

Time-frequency characterization of electrocorticographic recordings of epileptic patients using frequency-entropy similarity: a comparison to other bi-variate measures

Expert evaluation of electrocorticographic (ECoG) recordings forms the linchpin of seizure onset zone localization in the evaluation of epileptic patients for surgical resection. Numerous methods have been developed to analyze these complex recordings, including uni-variate (characterizing single channels), bi-variate (comparing channel pairs) and multivariate measures. Developing reliable algorithms may be helpful in clinical tasks such as localization of epileptogenic zones and seizure anticipation, as well as enabling better understanding of neuronal function and dynamics. Recently we have developed the frequency-entropy (F-E) similarity measure, and have tested its capability in mapping the epileptogenic zones. The F-E similarity measure compares time-frequency characterizations of two recordings. In this study, we examine the method's principles and utility and compare it to previously described bi-variate correspondence measures such as correlation, coherence, mean phase coherence and spectral comparison methods. Specially designed synthetic signals were used for illuminating theoretical differences between the measures. Intracranial recordings of four epileptic patients were then used for the measures' comparative analysis by creating a mean inter-electrode matrix for each of the correspondence measures and comparing the structure of these matrices during the inter-ictal and ictal periods. We found that the F-E similarity measure is able to discover spectral and temporal features in data which are hidden for the other measures and are important for foci localization.

The structural plasticity of white matter networks following anterior temporal lobe resection

Anterior temporal lobe resection is an effective treatment for refractory temporal lobe epilepsy. The structural consequences of such surgery in the white matter, and how these relate to language function after surgery remain unknown. We carried out a longitudinal study with diffusion tensor imaging in 26 left and 20 right temporal lobe epilepsy patients before and a mean of 4.5 months after anterior temporal lobe resection. The whole-brain analysis technique tract-based spatial statistics was used to compare pre- and postoperative data in the left and right temporal lobe epilepsy groups separately. We observed widespread, significant, mean 7%, decreases in fractional anisotropy in white matter networks connected to the area of resection, following both left and right temporal lobe resections. However, we also observed a widespread, mean 8%, increase in fractional anisotropy after left anterior temporal lobe resection in the ipsilateral external capsule and posterior limb of the internal capsule, and corona radiata. These findings were confirmed on analysis of the native clusters and hand drawn regions of interest. Postoperative tractography seeded from this area suggests that this cluster is part of the ventro-medial language network. The mean pre- and postoperative fractional anisotropy and parallel diffusivity in this cluster were significantly correlated with postoperative verbal fluency and naming test scores. In addition, the percentage change in parallel diffusivity in this cluster was correlated with the percentage change in verbal fluency after anterior temporal lobe resection, such that the bigger the increase in parallel diffusivity, the smaller the fall in language proficiency after surgery. We suggest that the findings of increased fractional anisotropy in this ventro-medial language network represent structural reorganization in response to the anterior temporal lobe resection, which may damage the more susceptible dorso-lateral language pathway. These findings have important implications for our understanding of brain injury and rehabilitation, and may also prove useful in the prediction and minimization of postoperative language deficits.