Predictive factors for success in surgical treatment for partial epilepsy: a multivariate analysis

Acute Postoperative Seizures and Engel Class Outcome at 1 Year Postselective Laser Amygdalohippocampal Ablation for Mesial Temporal Lobe Epilepsy

BACKGROUND

MRI-guided laser interstitial thermal therapy (MRgLITT) for mesial temporal lobe epilepsy is a safe, minimally invasive alternative to traditional surgical approaches. Prognostic factors associated with efficacy are debated; preoperative epilepsy duration and semiology seem to be important variables.

OBJECTIVE

To determine whether acute postoperative seizure (APOS) after MRgLITT for mesial temporal lobe epilepsy is associated with seizure freedom/Engel class outcome at 1 year.

METHODS

A single-institution retrospective study including adults undergoing first time MRgLITT for mesial temporal lobe epilepsy (2010-2019) with ≥1-year follow-up. Preoperative data included sex, epilepsy duration, number of antiepileptics attempted, weekly seizure frequency, seizure semiology, and radiographically verified anatomic lesion at seizure focus. Postoperative data included clinical detection of APOS within 7 days postoperatively, and immediate amygdala, hippocampal, entorhinal, and parahippocampal residual volumes determined using quantitative imaging postprocessing. Primary outcome was seizure freedom/Engel classification 1 year postoperatively.

RESULTS

Of 116 patients, 53% (n = 61) were female, with an average epilepsy duration of 21 (±14) years, average 6 failed antiepileptics (±3), and weekly seizure frequency of 5. APOS was associated with worse Engel class (P = .010), conferring 6.3 times greater odds of having no improvement vs achieving seizure freedom at 1 year. Residual amygdala, hippocampal, entorhinal, and parahippocampal volumes were not statistically significant prognostic factors.

CONCLUSION

APOS was associated with a lower chance of seizure freedom at 1 year post-MRgLITT for mesial temporal lobe epilepsy. Amygdala, hippocampal, entorhinal, and parahippocampal residual volumes after ablation were not significant prognostic factors.

Predicting hearing aid use in adults: the Beaver Dam Offspring Study

OBJECTIVE

The purpose of this study was to (i) develop a model that predicts hearing aid (HA) use and (ii) determine if model fit is improved by adding factors not typically collected in audiological evaluations.

DESIGN

Two models were created and evaluated. The "clinical" model used factors typically collected during audiologic clinical evaluations. The "expanded" model considered additional clinical, health and lifestyle factors to determine if the model fit could be improved (compared to clinical model). Models were created with least absolute shrinkage and selection operator (LASSO) logistic regression with 10-fold cross validation. Predictive ability was evaluated via receiver operating characteristic curves and concordance statistics (c-statistics).

STUDY SAMPLE

This study included 275 participants from the Beaver Dam Offspring Study, a prospective longitudinal cohort study of aging, with a treatable level of hearing loss and no HA use at baseline.

RESULTS

The clinical and expanded models report predictors important for HA use. The c-statistics of the clinical (0.80) and expanded (0.79) models were not significantly different (p = 0.41).

CONCLUSIONS

Similar predictive abilities of models suggest audiological evaluations perform well in predicting HA use.

Magnetic resonance-guided laser interstitial thermal therapy: Correlations with seizure outcome

OBJECTIVE

This study was undertaken to identify clinical factors associated with seizure freedom after magnetic resonance-guided laser interstitial thermal therapy (MRgLiTT) in temporal lobe epilepsy patients with unilateral mesial temporal sclerosis (MTS).

METHODS

We identified 56 patients with magnetic resonance imaging-defined MTS who underwent MRgLiTT with at least 1 year of follow-up. Primary outcome was seizure freedom at 1 year. We examined the association of seizure freedom and the following clinical factors: age at surgery, gender, history of febrile seizures, history of focal to bilateral tonic-clonic seizures, duration of epilepsy at the time of surgery, frequency of interictal epileptiform discharges (IEDs), seizure frequency, and presence of bilateral IEDs.

RESULTS

Thirty-five (62.5%) patients were seizure-free at 1 year. The presence of bilateral IEDs and age at surgery were associated with 1-year seizure freedom after MRgLiTT. The presence of bilateral IEDS was associated with lower odds of seizure freedom (odds ratio [OR] = .05, 95% confidence interval [CI] = .01-.46, p = .008), whereas increasing age at surgery was associated with increased odds of seizure freedom (OR = 1.10, 95% CI = 1.03-1.19, p = .009).

SIGNIFICANCE

This study demonstrates associations between presence of bilateral IEDs and age at surgery and seizure freedom at 1 year after MRgLiTT.

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.

A unique ictal EEG pattern in a patient with the coexistence of generalized and focal epilepsy

The coexistence of focal and generalized epilepsy is rare. We report on a 17-year-old male with drug-resistant focal epilepsy and idiopathic generalized epilepsy (IGE). He began to experience generalized tonic-clonic seizures (GTCS) at the age of 3 years, with a good response to phenobarbital. At the age of 14 years, he began to experience complex partial seizures (CPS). Video-electroencephalography (video-EEG) telemetry showed the coexistence of right temporal spikes and bursts of generalized spike-wave (GSW). The ictal EEG showed a unique EEG pattern characterized by a 4- to 5-second burst of GSW followed by rhythmic delta activity over the right temporal region. A magnetic resonance image (MRI) showed right hippocampal sclerosis. The patient underwent a right temporal lobectomy that significantly improved his seizure control. He was rendered seizure free of the complex partial seizures and improvement of the GTCS. This case illustrates a very uncommon ictal EEG pattern, and shows that the decision for surgery in patients with focal drug-resistant epilepsy should not be affected by coexistent generalized epilepsy.

Surgical approaches in nonlesional neocortical epilepsy

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

Presurgical neuropsychological testing predicts cognitive and seizure outcomes after anterior temporal lobectomy

We sought to determine significant predictors of seizure and cognitive outcome following surgery for epilepsy. Participants included 41 patients who had undergone anterior temporal lobectomy (ATL). Higher presurgical verbal/language scores and lower nonverbal memory scores were predictive of seizure-free status following ATL. Overall, the presurgical predictors were 93% accurate in discriminating between seizure-free and non-seizure-free patients postsurgery. Surgery in the nondominant-for-language hemisphere was predictive of higher postsurgical verbal/language and verbal memory scores. Higher presurgical visual/construction, nonverbal memory, and verbal/language scores were predictive of better postsurgical verbal/language functioning. Better presurgical verbal/language functioning was predictive of the same skills postsurgically as well as visual/construction outcomes. Exploratory analyses in a subset of participants (n=25) revealed that dominant and nondominant intracarotid amobarbital (Wada) memory scores added unique variance only for predicting nonverbal memory following ATL. Presurgical neuropsychological testing provides significant and unique information regarding postsurgical seizure freedom and cognitive outcome in patients who have undergone ATL.

Long-term outcome after temporal lobe epilepsy surgery in 434 consecutive adult patients

Object

The aim of this study was to evaluate the long-term efficacy of temporal lobe epilepsy (TLE) surgery and potential risk factors for seizure recurrence after surgery.

Methods

This retrospective study included 434 consecutive adult patients who underwent TLE surgery at Bethel Epilepsy Centre between 1991 and 2002.

Results

Hippocampal sclerosis was found in 62% of patients, gliosis in 17.3%, tumors in 20%, and focal cortical dysplasia (FCD) in 6.9%. Based on a Kaplan-Meier analysis, the probability of Engel Class I outcome for the patients overall was 76.2% (95% CI 71–81%) at 6 months, 72.3% (95% CI 68–76%) at 2 years, 71.1% (95% CI 67–75%) at 5 years, 70.8% (95% CI 65–75%) at 10 years, and 69.4% (95% CI 64–74%) at 16 years postoperatively. The likelihood of remaining seizure free after 2 years of freedom from seizures was 90% (95% CI 82–98%) for 16 years. Seizure relapse occurred in all subgroups. Patients with FCD had the highest risk of recurrence (hazard ratio 2.15, 95% CI 0.849–5.545). Predictors of remission were the presence of hippocampal atrophy on preoperative MR imaging and a family history of epilepsy. Predictors of relapse were the presence of bilateral interictal sharp waves and versive seizures. Six-month follow-up electroencephalography predicted relapse in patients with FCD. Short epilepsy duration was predictive of seizure remission in patients with tumors and gliosis; 28.1% of patients were able to discontinue antiepileptic medications without an increased risk of seizure recurrence (hazard ratio 1.05, 95% CI 0.933–1.20).

Conclusions

These findings highlight the role of etiology in prediction of long-term outcome after TLE surgery.

Neuronavigation applied to epilepsy monitoring with subdural electrodes

Accurate localization of the epileptogenic zone is of paramount importance in epilepsy surgery. Despite the availability of noninvasive structural and functional neuroimaging techniques, invasive monitoring with subdural electrodes is still often indicated in the management of intractable epilepsy. Neuronavigation is widely used to enhance the accuracy of subdural grid placement. It allows accurate implantation of the subdural electrodes based on hypotheses formed as a result of the presurgical workup, and can serve as a helpful tool for resection of the epileptic focus at the time of grid explantation. The authors describe 2 additional simple and practical techniques that extend the usefulness of neuronavigation in patients with epilepsy undergoing monitoring with subdural electrodes. One technique involves using the neuronavigation workstation to merge preimplantation MR images with a postimplantation CT scan to create useful images for accurate localization of electrode locations after implantation. A second technique involves 4 holes drilled at the margins of the craniotomy at the time of grid implantation; these are used as fiducial markers to realign the navigation system to the original registration and allow navigation with the merged image sets at the time of reoperation for grid removal and resection of the epileptic focus. These techniques use widely available commercial navigation systems and do not require additional devices, software, or computer skills. The pitfalls and advantages of these techniques compared to alternatives are discussed.

The surgery of epilepsy

The idea of surgical treatment for epilepsy is not new. However, widespread use and general acceptance of this treatment has only been achieved during the past three decades. A crucial step in this direction was the development of video electroencephalographic monitoring. Improvements in imaging resulted in an increased ability for preoperative identification of intracerebral and potentially epileptogenic lesions. High resolution magnetic resonance imaging plays a major role in structural and functional imaging; other functional imaging techniques (e.g., positron emission tomography and single-photon emission computed tomography) provide complementary data and, together with corresponding electroencephalographic findings, result in a hypothesis of the epileptogenic lesion, epileptogenic zone, and the functional deficit zone. The development of microneurosurgical techniques was a prerequisite for the general acceptance of elective intracranial surgery. New less invasive and safer resection techniques have been developed, and new palliative and augmentative techniques have been introduced. Today, epilepsy surgery is more effective and conveys a better seizure control rate. It has become safer and less invasive, with lower morbidity and mortality rates. This article summarizes the various developments of the past three decades and describes the present tools for presurgical evaluation and surgical strategy, as well as ideas and future perspectives for epilepsy surgery.

Predictive factors for postoperative outcome in temporal lobe epilepsy according to two different classifications

PURPOSE

The determination of prognostic factors is important for predicting outcome after epilepsy surgery. We investigated the factors related to surgical outcome within a homogeneous group of patients suffering from pathologically proven mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS), and compared Engel's outcome classification system with the latest one proposed by the ILAE.

METHOD

We included 109 patients with MTLE-HS who were followed-up for at least 1 year after epilepsy surgery. A retrospective chart review was performed to extract patients' demographic details, and potential pre-postoperative risk factors. Outcome of surgery was defined by the Engel's and ILAE classifications. In addition, the course of prognosis was determined according to the changes in ILAE classifications on an annual basis. Univariate and multivariate logistic regression analyses were used for the latest available outcomes and two different courses of prognosis.

RESULTS

The average duration of follow up was 4.78+/-2.55 years in the 109 patients with MTLE-HS. The univariate and multiple logistic regression analyses showed that the occurrence of seizures during the first month after surgery was a significant risk factor for a poor outcome. A history of trauma was also significant for patients with late recurrence of postsurgical seizures after at least 1-year seizure remission.

CONCLUSION

The occurrence of seizures during the first month after surgery is a significant prognostic factor in patients with MTLE-HS. Ignoring early postoperative seizures in classification systems may result in difficulty in identifying the course of epilepsy after surgery.

Frontal lobe epilepsy: clinical characteristics, surgical outcomes and diagnostic modalities

OBJECTIVE

To identify surgical prognostic factors and to characterize clinical features according to the location of the intracranial ictal onset zone of frontal lobe epilepsy (FLE) in order to assess the role of various diagnostic modalities, including concordances with presurgical evaluations.

METHODS

We studied 71 FLE patients who underwent epilepsy surgery and whose outcomes were followed for more than 2 years. Diagnoses were established by standard presurgical evaluation.

RESULTS

Clinical manifestations could be categorized into six types: initial focal motor (9 patients), initial versive seizure (15), frontal lobe complex partial seizure (14), complex partial seizure mimicking temporal lobe epilepsy (18), initial tonic elevation of arms (11), and sudden secondary generalized tonic-clonic seizure (4). Thirty-seven patients became seizure-free after surgery. Five patients were deleted in the analysis because of incomplete resection of ictal onset zones. The positive predictive value of interictal EEG, ictal EEG, MRI, PET, and ictal SPECT, respectively were 62.5%, 56.4%, 73.9%, 63.2%, and 63.6%, and the negative predictive value were 46.0%, 44.4%, 53.5%, 44.7%, and 51.7%. No significant relationship was found between the diagnostic accuracy of these modalities and surgical outcome, with the exception of MRI (p=0.029). Significant concordance of two or more modalities was observed in patients who became seizure-free (p=0.011). We could not find any clinical characteristic related to surgical outcome besides seizure frequency. No definite relationship was found between the location of intracranial ictal onset zone and clinical semiology.

CONCLUSION

Although various diagnostic methods can be useful in the diagnosis of FLE, only MRI can predict surgical outcome. Concordance between presurgical evaluations indicates a better surgical outcome.

Factors predicting seizure outcome of anterior temporal lobectomy for patients with mesial temporal sclerosis

PURPOSE

To investigate the factors, including those associated with ictal scalp EEG results, related to surgical outcome in patients with pathologically proven mesial temporal sclerosis.

METHODS

We studied 51 consecutive patients who underwent anterior temporal lobectomy and had at least 4 years of follow-up. Surgical outcome was classified as being seizure-free or not seizure-free during the first two and the subsequent two postoperative years. Clinical variables and scalp EEG parameters were subjected to statistical analysis.

RESULTS

Of the 51 patients, 36 (70.6%) were seizure-free during postoperative years 3 and 4. Logistic regression analysis revealed that seizure remission for the first 2 years (p = 0.002) and contralateral propagated ictal discharges (p = 0.015) were independently related to seizure outcome at 4 years. Patients who were seizure-free at 2 years had an 86.5% chance of remaining seizure-free at 4 years. Of the patients without bitemporal asynchrony or switch of lateralization, 88.9% were seizure free at 4 years, compared with 54.5% of patients with asynchrony or switch of lateralization (p = 0.007). These two factors, however, were not predictive of seizure outcome at 2 years.

CONCLUSIONS

Contralateral propagated ictal discharges, including bitemporal asynchrony and switch of lateralization, unfavorably influence long-term seizure outcome. Long-term seizure control is best when the patient has no such propagation patterns of ictal discharges and is seizure-free during the first 2 years after temporal lobectomy.

Late seizures in patients initially seizure free after epilepsy surgery

PURPOSE

Surgery for medically intractable epilepsy is currently the most effective means of achieving seizure control. Although relatively few long-term outcome studies have been performed, evidence is mounting that the possibility of late seizure recurrence exists, even after an early seizure-free period. No published reports document the rate and predictors of late recurrence in a large series of patients undergoing surgery in the magnetic resonance imaging (MRI) era.

METHODS

We retrospectively queried the databases of two epilepsy surgery centers. Patients eligible for study had preoperative MRI scans, were seizure free for 1 year after surgery, and had a minimal follow-up period of 3 years. Patients with tumors or vascular lesions were excluded. We performed log-rank comparison of Kaplan-Meier product limit estimates for categoric variables and used a Cox proportional hazards model for continuous variables. Variables that were significant (p<0.05) on a univariate screen were entered into a multivariate forward step-wise Cox regression.

RESULTS

The study included 285 patients, 254 with medial temporal lobe (MTLE) and 31 with neocortical epilepsy. The probability of having a single seizure after being seizure free for 1 year was 18.3% at 5 years and 32.7% at 10 years. However, only 13% were not seizure free at the last follow-up. Predictors of late recurrences on both uni- and multivariate analysis were the presence of preoperative generalized tonic-clonic (GTC) seizures in patients with neocortical epilepsy and late age at surgery in patients with MTLE. MRI results and location of surgery were not predictive.

CONCLUSIONS

Although the risk of at least one recurrent seizure after initially successful epilepsy surgery is relatively high, the rate of recurrent intractability is low. The finding that late age at surgery and presence of preoperative GTC seizures are predictors of late recurrence indicates the importance of patient selection and early surgery for persistent seizure control.

Long-term outcome of epilepsy surgery among 399 patients with nonlesional seizure foci including mesial temporal lobe sclerosis

OBJECT

The authors reviewed the long-term outcome of focal resection in a large group of patients who had intractable partial nonlesional epilepsy, including mesial temporal lobe sclerosis (MTS), and who were treated consecutively at a single institution. The goal of this study was to evaluate the long-term efficacy of epilepsy surgery and the preoperative factors associated with seizure outcome.

METHODS

This retrospective analysis included 399 consecutive patients who underwent epilepsy surgery at Mayo Clinic in Rochester, Minnesota, between 1988 and 1996. The mean age of the patients at surgery was 32 +/- 12 years (range 3-69 years), and the mean age at seizure onset was 12 +/- 11 years (range 0-55 years). There were 214 female (54%) and 185 male (46%) patients. The mean duration of epilepsy was 20 +/- 12 years (range 1-56 years). The preceding values are given as the mean +/- standard deviation. Of the 399 patients, 237 (59%) had a history of complex partial seizures, 119 (30%) had generalized seizures, 26 (6%) had simple partial seizures, and 17 (4%) had experienced a combination of these. Preoperative evaluation included a routine and video-electroencephalography recordings, magnetic resonance imaging of the head according to the seizure protocol, neuropsychological testing, and a sodium amobarbital study. Patients with an undefined epileptogenic focus and discordant preoperative studies underwent an intracranial study. The mean duration of follow up was 6.2 +/- 4.5 years (range 0.6-15.7 years). Seizure outcome was categorized based on the modified Engel classification. Time-to-event analysis was performed using Kaplan-Meier curves and Cox regression models to evaluate the risk factors associated with outcomes. Among these patients, 372 (93%) underwent temporal and 27 (7%) had extratemporal resection of their epileptogenic focus. Histopathological examination of the resected specimens revealed MTS in 113 patients (28%), gliosis in 237 (59%), and normal findings in 49 (12%). Based on the Kaplan-Meier analysis, the probability of an Engel Class I outcome (seizure free, auras, or seizures related only to medication withdrawal) for the overall patient group was 81% (95% confidence interval [CI] 77-85%) at 6 months, 78% (CI 74-82%) at 1 year, 76% (CI 72-80%) at 2 years, 74% (CI 69-78%) at 5 years, and 72% (CI 67-77%) at 10 years postoperatively. The rate of Class I outcomes remained 72% for 73 patients with more than 10 years of follow up. If a patient was in Class I at 1 year postoperatively, the probability of seizure remission at 10 years postoperatively was 92% (95% CI 89-96%); almost all seizures occurred during the 1st year after surgery. Factors predictive of poor outcome from surgery were normal pathological findings in resected tissue (p = 0.038), male sex (p = 0.035), previous surgery (p < 0.001), and an extratemporal origin of seizures (p < 0.001).

CONCLUSIONS

The response to epilepsy surgery during the 1st follow-up year is a reliable indicator of the long-term Engel Class I postoperative outcome. This finding may have important implications for patient counseling and postoperative discontinuation of anticonvulsant medications.

Race/ethnicity: a predictor of temporal lobe epilepsy surgery outcome?

PURPOSE

The success of epilepsy surgery in temporal lobe epilepsy reaches a 64% rate of seizure freedom, based on a randomized control trial. Observational studies from epilepsy centers worldwide indicate seizure freedom rates up to 93% when the etiology is unilateral hippocampal sclerosis. Several risk factors are attributed to the recurrence of seizures following the surgical procedure. Nonetheless, whether race influences the outcome of temporal lobe surgery is unknown. The purpose of this study was to evaluate if race plays a role in outcome following surgery.

METHODS

Data were obtained from the discharge database of the University of Alabama at Birmingham video/EEG monitoring unit, between 1998 and 2003, as well as the clinical charts. Seizure recurrence was evaluated 1 year following surgery. The sample consisted of all patients with a primary diagnosis of mesial temporal sclerosis (MTS) who underwent anterior temporal lobectomy. Multiple logistic regression analysis was used to model the presence of seizure recurrence after anterior temporal lobectomy for MTS. Two sets of logistic regression models were estimated to generate odds ratios (ORs) for seizure recurrence after an anterior temporal lobectomy for African-Americans or other possible ethnic/racial group present relative to non-Hispanic Caucasians. The first model incorporated only ethnicity as the independent variable and generated unadjusted ORs for seizure recurrence following the surgical procedure. The second set included the independent variables: duration of epilepsy, history of febrile seizures, lateralization of epileptogenic focus, handedness, and age.

RESULTS

Seventy patients underwent surgical treatment and all of them had pathologic confirmation of MTS. Follow-up information for six was not available. Analysis of the remaining 64 patients revealed that African-Americans were more likely than non-Hispanic Caucasians to have seizure recurrence after surgery (OR=2.1, 95% CI=0.6-8.0). After potential confounders (duration of epilepsy, history of febrile seizures, lateralization of epileptogenic focus, handedness, and age) were controlled, this finding did not change (OR=1.7, 95% CI=0.3-10.7).

CONCLUSION

Our data suggest that race may be an important factor related to seizure outcome following temporal lobectomy.

Vagus nerve stimulation: predictors of seizure freedom

OBJECTIVES

To identify predictive factors for the seizure-free outcome of vagus nerve stimulation (VNS).

METHODS

All 47 patients who had undergone VNS implantation at one centre and had at least one year of follow up were studied. They underwent complete presurgical evaluation including detailed clinical history, magnetic resonance imaging, and long term video-EEG with ictal and interictal recordings. After implantation, adjustment of stimulation parameters and concomitant antiepileptic drugs were at the discretion of the treating physician.

RESULTS

Mean (SD) age of the patients was 22.7 (11.6) years (range 7 to 53). Six patients (13%) became seizure-free after the VNS implantation. Only two variables showed a significant association with the seizure-free outcome: absence of bilateral interictal epileptiform discharges (IED) and presence of malformation of cortical development (MCD). Epilepsy duration showed a non-significant trend towards a negative association with outcome. By logistic regression analysis, only absence of bilateral IED correlated independently with successful VNS treatment (p<0.01, odds ratio = 29.2 (95% confidence interval, 2.4 to 353)). Bilateral IED (independent or bilateral synchronous) was found in one of six seizure-free patients and in 33 of 41 non-seizure-free patients. When bilateral IED were absent, the sensitivity for seizure-free outcome was 0.83 (0.44 to 0.97), and the specificity was 0.80 (0.66 to 0.90).

CONCLUSIONS

Bilateral IED was independently associated with the outcome of VNS. These results are preliminary because they were based on a small patient population. They may facilitate prospective VNS studies enrolling larger numbers of patients to confirm the results.

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.

Parietal Lobe Epilepsy: Surgical Treatment and Outcome

OBJECTIVE

Parietal lobe epilepsy (PLE) is neither common nor easily diagnosed because of its variable clinical features. To elucidate its characteristics and surgical outcome, the authors reviewed their surgical experiences.

METHODS

Between September 1994 and August 2001, 38 patients with PLE received surgical treatment at the Seoul National University Hospital. All patients underwent resection, mainly involving the parietal lobe.

RESULTS

Preoperatively, over 60% of the cases were not considered to be PLE, even though PLE was the most common diagnosis (15/38, 39.8%). An invasive study was performed in 37 of the 38 patients. Awake operations under regional anesthesia were performed in 20 patients (52.6%). Seizure disappeared in 15 (Engel's classification I, 39.5%), and rare seizure remained in 5 (Engel II, 13.2%). Thirteen patients showed a worthwhile improvement (Engel III, 34.2%), whereas 5 exhibited no worthwhile improvement (Engel IV, 13.2%). Pathologies were diverse, the most common being cortical dysplasia (94.3%).

CONCLUSION

Since PLE is difficult to diagnose preoperatively, an invasive study covering the parietal lobe is mandatory, if PLE is suspected. Cortical dysplasia was the most common etiology, thus awake operation under regional anesthesia and intraoperative brain mapping is helpful during extensive resection in order to spare the eloquent cortex.

Predictors of seizure outcome after temporal lobectomy for intractable epilepsy

OBJECTIVES

To assess predictors of outcome of temporal lobectomy for intractable epilepsy.

MATERIAL AND METHODS

In 63 adult patients operated with anterior temporal lobectomy during 198892, we used logistic regression analysis to assess predictors of being seizure-free (Engel's class I) 2 years after surgery. As potential predictors, we included the following variables: gender, age at operation, age at onset of seizures, epilepsy duration, etiology, generalized vs not generalized seizures, seizure frequency, intelligence quotient, ictal electroencephalography, magnetic resonance imaging (MRI), single-photon emission computed tomography (SPECT), side of resection, and extent of the resection.

RESULTS

About 44% of the surgery patients were seizure-free (Engel's class I) 2 years after surgery. In multivariate analysis (n = 55), MRI pathology defined as atrophy in the temporal lobe, angioma, tumor or mesial temporal sclerosis (odds ratio, OR 7.4, 95%CI: 1.7-32.9) and extent of the hippocampal resection (increase of 1 cm) (OR 2.2, 95%CI: 1.1-4.6) predicted being seizure-free.

CONCLUSION

Focal pathology in preoperative MRI and the extent of the hippocampal resection were the only significant predictors of being seizure-free after 2 years.

Indices of resective surgery effectiveness for intractable nonlesional focal epilepsy

Among 70 patients with intractable focal epilepsy and no specific lesion, as determined by both MRI (magnetic resonance imaging) and histopathology, outcome after resective surgery was polarized: 26 (37%) became seizure free (SF), and 27 (39%) were not helped. Eighteen (42%) of 43 standard temporal resections rendered patients SF, somewhat more than eight (30%) of 27 other procedures. To seek reliable prognostic factors, the subsequent correlative data compared features of the 26 SF patients with those of the 27 not helped. Although ictal semiology guided the site of surgical resection, it and other aspects of seizure and neurologic history failed to predict surgical outcome. However, two aspects of preoperative scalp EEGs correlated with SF outcomes: (a) among 25 patients in whom >50% of clinical seizures arose from the later resected lobe and no other origins, 18 (72%) became SF compared with seven (28%) of 25 with other ictal profiles; (b) 13 (93%) of 14 temporal lobe patients whose interictal and ictal EEGs lacked features indicative of multifocal epileptogenesis became SF compared with five (33%) of 15 with such components. The considered need for subdural (SD) EEG reduced SF outcome from 18 (90%) of 20 patients without SD to eight (24%) of 33 with SD; this likely reflected an insufficient congruity of ictal semiology and interictal and ictal scalp EEG for localizing epileptogenesis. Within this SD group, >50% of clinical seizure origins from a later resected lobe increased SF outcome somewhat: from two (14%) of 14 without this attribute to six (40%) of 15 with it; 100% of such origins increased SF outcome from two (12%) of 16 to six (46%) of 13.

Resective Surgery for Intractable Focal Epilepsy in Patients with Low IQ: Predictors for Seizure Control and Outcome with Respect to Seizures and Neuropsychological and Psychosocial Functioning

PURPOSE

To investigate possible predictive factors for seizure control in a group of children and adults with low IQs (IQ, < or =70) who underwent resective surgery for intractable focal epilepsy and to study outcome with respect to seizures and neuropsychological functioning. We also studied psychosocial outcome in the adult patients.

METHODS

Thirty-one patients (eight children younger than 18 years) with a Wechsler Full Scale IQ of 70 or less underwent comprehensive neuropsychological assessments before and 2 years after surgery. Adults also completed the Washington Psychosocial Seizure Inventory (WPSI). Univariate analyses were used to identify variables differentiating between patients who became seizure free and those who did not. Pre- and postoperative test results were compared by t test for dependent samples.

RESULTS

Forty-eight percent of the patients became seizure free, 52% of those with temporal lobe resection and 38% of those with extratemporal resection. Only one variable was predictive for seizure outcome: duration of epilepsy. In one third of the patients, who had the shortest duration of epilepsy (<12 years), 80% became seizure free. Significant improvement was seen regarding vocational adjustment in adults (WPSI). Seizure-free adults improved their Full Scale IQ scores. No cognitive changes were found in seizure-free children or in patients who did not become seizure free.

CONCLUSIONS

A good seizure outcome was obtained after resective surgery in patients with intractable focal epilepsy and low IQ, provided that treatment was done relatively shortly after onset of epilepsy. No adverse effects were seen on cognitive and psychosocial functioning.

MRI and EEG findings in surgically treated patients with partial seizures due to neuronal migration disorders, their relations to each other and to surgery outcome

OBJECTIVES

To evaluate magnetic resonance imaging (MRI) and electro-encephalogram (EEG) findings of patients with therapy-resistant partial seizures due to neuronal migration disorders (NMD), and compare them with each other and with surgery outcome.

MATERIAL AND METHODS

The MRI, interictal and ictal EEG findings, and their relations to each other in 41 patients with NMD were compared with class IA surgery outcome.

RESULTS

The patients showed an MRI lesion in decreasing frequency from the frontal to the occipital areas. A predominantly extratemporal location of the interictal EEG foci (73.3%) and ictal patterns (82.4%) was therefore apparent, also showing a diminishing frequency from the anterior to the posterior areas. Comparing the EEG foci with the MRI lesions, the same location of the interictal foci was found in 68.4% and of the ictal foci in 52.7%, including several cases with a more widespread EEG focus or MRI lesion. The same location of interictal as well as ictal foci was evident in 85.7%. The most favourable surgery outcome (class IA) was, on average, apparent in patients with an MRI lesion (28.6% vs 25%), a main interictal EEG focus (50% vs 18%) and an ictal seizure pattern (37.5% vs 16.7%) located in the temporal area; likewise, if the interictal focus (30.8% vs 18.2%) and the ictal pattern (31.8% vs 12.5%) showed the same location as the MRI lesion, as well as when the interictal and ictal EEG changes had an equal location (30% vs 20%).

CONCLUSION

MRI and EEG recordings show relatively close relations to each other and might be important methods to predict surgery outcome in NMD patients.

Factors predicting outcome of surgery for intractable epilepsy with pathologically verified mesial temporal sclerosis

PURPOSE

To examine the subgroup of patients with medically intractable epilepsy receiving temporal lobectomies who have pathologically verified mesial temporal sclerosis (MTS) and to determine the relation of demographic and clinical factors, results of diagnostic testing, and details of the surgical procedure with prognosis for achieving control of seizures.

METHODS

All patients receiving surgical treatment for intractable epilepsy between 1991 and 1998 at the University of Washington were reviewed. There were 118 patients who met inclusion criteria of adequate pathological analysis showing MTS without a progressive process and a minimum of 1-year follow-up.

RESULTS

Only personal history of status epilepticus demonstrated significant (p = 0.0276) prediction of outcome, increasing the risk of surgical failure. No other factors were significant predictors of outcome, including history of febrile seizures, possible etiologic factors, EEG, magnetic resonance imaging (MRI) or neuropsychological testing results, or extent of resection.

CONCLUSIONS

Many factors that have been previously described to predict favorable outcome in the overall group of patients receiving temporal lobe resections for intractable epilepsy are, in fact, predictors of MTS and lose their predictive value when the subgroup of patients with confirmed MTS is examined. Neurosurgical treatment of MTS can be very effective even in the presence of significant etiologic factors, or of bilateral or extratemporal abnormalities on EEG or MRI.

Prognostic factors and outcome after different types of resection for temporal lobe epilepsy

OBJECT

It is unknown whether different resection strategies for temporal lobe epilepsy (TLE) produce alterations in seizure control or neuropsychological performance.

METHODS

A series of 321 patients who underwent surgery for TLE between 1989 and 1997 was submitted to a uni- and multifactorial analysis of clinical, electrophysiological, neuroimaging, neuropsychological, and surgical factors to determine independent predictors of outcome. Until 1993, most patients with TLE underwent standard anterior temporal lobectomy (ATL); beginning in 1993, surgical procedures were increasingly restricted to lesions detected on magnetic resonance (MR) imaging and the presumed epileptogenic foci: for example, amygdalohippocampectomy (AH) or lesionectomy/corticectomy began to be used more often. The mean follow-up duration in this study was 38 months. Two hundred twenty-seven patients were classified as seizure free (70.7%), and 36 patients had rare and nondisabling seizures (11.2%); these groups were summarized as having good seizure control (81.9%). Twenty-four patients attained more than 75% improvement (7.5%), and no worthwhile improvement was seen in 34 cases (10.6%); these groups were summarized as having unsatisfactory seizure control (18.1%). On unifactorial analysis the following preoperative factors were associated with good seizure control (p < 0.05): single and concordant lateralizing focus on electroencephalography studies, low seizure frequency, absence of status epilepticus, concordant lateralizing memory deficit, clear abnormality on MR images, suspected ganglioglioma or dysembryoplastic neuroepithelial tumor (DNT), and absence of dysplasia on MR images. Stepwise logistic regression revealed a model containing five factors that were predictive for good seizure control (p < 0.1): 1) clear abnormality on MR images; 2) absence of status epilepticus; 3) MR imaging-confirmed ganglioglioma or DNT; 4) concordant lateralizing memory deficit; and 5) absence of dysplasia on MR images. Seizure outcome was mainly correlated with diagnosis and clinical factors. No significant differences were found regarding different resection types performed for comparable tumors. Neuropsychological testing revealed better postoperative results after limited resections compared with standard ATL, especially with regard to attention level, verbal memory, and calculated total neuropsychological performance.

CONCLUSIONS

Different strategies for surgical approaches in TLE result in equally good outcomes. Seizure outcome is mainly dependent on the diagnosis and clinical factors, whereas the neuropsychological results are more beneficial after resections limited to an epileptogenic lesion and focus.

Frequency and significance of acute postoperative seizures following epilepsy surgery in children and adolescents

PURPOSE

To determine the frequency and prognostic features of acute postoperative seizures (APOSs), within the first postoperative week, in a group of children undergoing surgery for the treatment of medically refractory epilepsy.

METHODS

Patients younger than 18 years who underwent surgery for the relief of medically intractable epilepsy at the Mayo Clinic between 1985 and 1998 with a minimum of 12 months of follow-up were eligible. A retrospective chart review was conducted to abstract information regarding demographics, epilepsy history, and preoperative, intraoperative, and postoperative risk factors, APOSs, and outcome. A multivariate analysis was conducted to control for confounding variables.

RESULTS

The study group was composed of 148 patients (mean age at surgery, 13 years; range, 5 months to 18 years). Twenty-five percent of patients experienced APOSs. Risk factors associated with a statistically significant (p < 0.05) greater likelihood of experiencing APOS were non-complex partial seizure type, extratemporal surgery, postoperative fever, non-temporal lobe epilepsy, and postoperative interictal epileptiform activity. At last follow-up, patients who did not experience APOSs had a significantly greater chance of being seizure free (80 vs. 51%; p < 0.001). With a multivariate analysis, APOS was found to be an independent predictor of outcome.

CONCLUSIONS

This study indicates that APOSs are predictive of a less favorable outcome in the pediatric postsurgical patient; however, 51% remained seizure free at last follow-up. Finally, the effects of APOSs on outcome were shown to be stable over a 12-month follow-up period.

Is refractory epilepsy preventable?

About a third of the patients diagnosed with epilepsy will not be fully controlled with antiepileptic drugs (AEDs), and many of them will have frequent and disabling seizures. These patients will undergo multiple drug trials, most often without complete seizure remission. Moreover, refractory epilepsy is associated with increased morbidity (from seizures and medications), social isolation, unemployment, and overall reduced quality of life. There is evidence that refractory epilepsy can be a progressive disorder, which, if controlled early, might never develop into a full syndrome with all of its associated sequelae. The difficulty lies in identifying at an early stage patients who are likely to progress to intractability. No currently known markers enable clinicians to make this identification with confidence. Advances in pharmacogenomics and our understanding of pharmacologic responsiveness in epilepsy may change this situation. Even now, we are able to identify many patients with a poor prognosis earlier than before, particularly in the pediatric population, in which syndromic classification may provide an approach to predict intractability. The early initiation of aggressive therapy may improve outcome and overall quality of life.

Relevance of residual histologic and electrocorticographic abnormalities for surgical outcome in frontal lobe epilepsy

PURPOSE

To estimate the significance of residual electrocorticographic and neuropathologic abnormalities on seizure control after surgery for frontal lobe epilepsy with the purpose of determining their relevance in deciding the extent of the surgical procedure.

METHODS

The presence of epileptiform discharges in intraoperative electrocorticograms (ECoGs) and the nature and extent of neuropathologic abnormalities were reviewed for 35 patients who underwent frontal lobe resections for the treatment of epilepsy at our institution. The relations between surgical outcome and presence of the following features were studied: (a) presence of abnormal tissue at the limits of the resection; (b) presence of sporadic spikes and seizure patterns in the preresection ECoG; (c) their abolition in the postresection ECoG; and (d) the topography of residual discharges with respect to the margins of the resection.

RESULTS

On neuropathologic examination, 18 patients showed focal cortical dysplasia (CD), and 17 showed other abnormalities (non-CD). Ten CD patients and 11 non-CD patients experienced a favourable outcome. Seizure patterns were significantly more common in patients with focal cortical dysplasia than in those without, with a sensitivity of 94% and a specificity of 75%. Abolition of seizure patterns was associated with a favourable surgical outcome (p = 0.031). Abolition of sporadic spikes or their presence in the postresection ECoG did not influence outcome. There was no clear relation between outcome and location of residual sporadic discharges. Seizure patterns persisted in the postresection ECoG in three CD patients, were located at the margins of the resection in all three, and these patients had a poor outcome. Incomplete removal of abnormal tissue was not associated with a poorer outcome in either patient group or in the complete sample.

CONCLUSIONS

Seizure patterns were significantly more common in patients with cortical dysplasia, and their abolition on postresection ECoG recordings was associated with a favourable surgical outcome. Persistence of sporadic ECoG spikes and incomplete removal of histologic abnormalities did not affect outcome significantly.

Predictors of seizure outcome in newly diagnosed partial epilepsy: memory performance as a prognostic factor

The epilepsy patients whose seizures will prove to be refractory should be identified as early as possible, and thus the need for new prognostic factors of intractable epilepsy is evident. The aim of the study was to investigate predictors of seizure outcome in a multivariate analysis. Neurological, electroencephalography (EEG) and neuropsychological variables were analyzed as potential predictors of epilepsy. Eighty-nine newly diagnosed adult patients with partial epilepsy were, after a prospective 2-year follow-up period, categorized into one of the two groups: patients with satisfactorily controlled epilepsy, and patients with refractory epilepsy. Six variables predicted 2-year seizure outcome: presence of spike focus in EEG, partial complex or mixed seizure type, remote symptomatic etiology, moderately impaired memory performance in immediate recall and in delayed recognition of the word list, and age at the time of diagnosis. The correct seizure outcome could be predicted with the model in 94% of newly diagnosed epilepsy patients. The presence of verbal memory impairment at the time of the diagnosis of partial epilepsy is a significant predictor of seizure outcome and, together with clinical and EEG variables, it predicts seizure outcome in the majority of the patients. Memory performance as a prognostic factor is of most value in patients with risk of refractory epilepsy and when used in a multidisciplinary setting.

Neural network analysis of preoperative variables and outcome in epilepsy surgery

OBJECT

Because appropriate patient selection is essential for achieving successful outcomes after epilepsy surgery, the need for more robust methods of predicting postoperative seizure control has been created. Standard multivariate techniques have been only 75 to 80% accurate in this regard. Recent use of artificial intelligence techniques, including neural networks, for analyzing multivariate clinical data has been successful in predicting medical outcome.

METHODS

The authors applied neural network techniques to 80 consecutive patients undergoing epilepsy surgery in whom data on demographic, seizure, operative, and clinical variables to predict postoperative seizures were collected. Neural networks could be used to predict postoperative seizures in up to 98% of cases. Student's t-tests or chi-square analysis performed on individual variables revealed that only the preoperative medication index was significantly different (p = 0.02) between the two outcome groups. Six different combinations of input variables were used to train the networks. Neural network accuracies differed in their ability to predict seizures: using all data (96%); all data minus electroencephalography concordance and operative side (93%); all data except intra- or postoperative variables such as tissue pathological category (98%); all data excluding pathological category, intelligence quotient (IQ) data, and Wada results (84%); only demographics and tissue pathological category (65%); and only IQ data (63%).

CONCLUSIONS

Analysis of the results reveals that several networks that are trained with the usual accepted variables characterizing the typical evaluation of epilepsy patients can predict postoperative seizures with greater than 95% accuracy.

Prognostic factors in presurgical assessment of frontal lobe epilepsy

OBJECTIVES

To determine predictors for surgical outcome in the presurgical assessment of frontal lobe epilepsy.

METHODS

Thirty seven patients were operated on for frontal lobe epilepsy between 1975 and 1996. Their medical records were reviewed for ictal semiology, age at onset, duration of the epilepsy, age at operation, preoperative interictal and ictal encephalographic findings, and abnormalities on neuroimaging and neuropsychological testing. In addition, type of resection and pathology were compared with surgical outcome.

RESULTS

Univariate statistical analysis showed that the presence of a focal abnormality on neuroimaging was associated with favourable outcome. The presence of the following ictal findings was associated with poor outcome: autonomic manifestations, eye deviation, head version contralateral to the operated side, and bilateral or multifocal ictal onset. Fifteen patients had secondarily generalised interictal discharges and, interestingly, their presence was not associated with poor outcome. Multivariate logistic regression showed that the presence of a focal abnormality on neuroimaging was significantly associated with a favourable outcome while contralateral head version was the only variable significantly associated with poor surgical outcome.

CONCLUSIONS

A focal abnormality on neuroimaging was the only variable which was significantly associated with a favourable surgical outcome, whereas contralateral head version was the most significant predictor for a poor outcome. The presence of generalised discharges before surgery was not associated with poor outcome.

Neural network analysis of preoperative variables and outcome in epilepsy surgery

Because appropriate patient selection is essential for achieving successful outcomes after epilepsy surgery, the need for more robust methods of predicting postoperative seizure control has been created. Standard multivariate techniques have been only 75 to 80% accurate in this regard. Recent use of artificial intelligence techniques, including neural networks, for analyzing multivariate clinical data, has been successful in predicting medical outcome. The authors applied neural network techniques to 80 consecutive patients undergoing epilepsy surgery in whom demographic, seizure, operative, and clinical variables to predict postoperative seizures data were obtained.

Neural networks were able to predict postoperative seizures in up to 98% of cases. Student's t tests or chi-square analysis performed on individual variables revealed that only the preoperative medication index was significantly different (p = 0.02) between the two outcome groups. Six different combinations of input variables were used to train the networks. Neural network accuracies differed in their ability to predict seizures using all data (96%); all data minus electroencephalography concordance and operative side (93%); all data except intra- or postoperative variables such as tissue pathology (98%); all data excluding pathology, intelligence quotient (IQ) data, and Wada results (84%); only using demographics and tissue pathology (65%); and only using IQ data (63%).

Analysis of the results reveals that several networks that are trained with the usual accepted variables characterizing the typical evaluation of epilepsy patients can predict postoperative seizures with greater than 95% accuracy.

Multivariable prediction of seizure outcome one year after resective epilepsy surgery: development of a model with independent validation

PURPOSE

To identify predictors of seizure-outcome after epilepsy surgery and validate the findings in an independent series of patients. To use the results to develop a predictive model.

METHODS

Sequential patients undergoing resective surgery for medically intractable epilepsy were identified at Yale New Haven Hospital (1987-1990, group 1) and Columbia Presbyterian Hospital (1991-1994, group 2). Information about seizure outcome and predictors of outcome was obtained from medical chart review. Good seizure-outcome was defined as having been seizure-free for one year beginning with discharge from the hospital. Multiple logistic regression was used to develop a model of predictors in group 1. It was then validated in group 2.

RESULTS

There were 133 patients in group 1 and 81 in group 2. In a multivariable analysis, independent predictors of outcome in group 1 were presence of mesial temporal sclerosis based on postsurgical pathological analysis (MTS) (relative risk (RR) = 1.47), having a known underlying etiology (RR = 1.32), and partial seizures only (RR = 1.17). In group 2, the findings for each factor were similar to those in group 1: MTS, RR = 1.49; etiology, RR = 1.32; and partial seizures, RR = 1.24. Used in combination, these three factors can identify patients with nearly a 100% chance of being seizure-free (all three factors present) versus less than a 50% chance (none of the three factors present).

CONCLUSIONS

With independent validation of the findings, we can be reasonably certain that the three factors identified in this analysis are meaningful and generalizable predictors of seizure outcome following epilepsy surgery. Use of predictive models should be considered in future studies to convert study results into clinically relevant statements about a particular patient's likelihood of surgical success.

Surgical treatment for epilepsy: a retrospective Swedish multicenter study

The characteristics of patients suffering from drug resistant epilepsy, including the results of the preoperative evaluation and epilepsy surgery were retrospectively analyzed in a Swedish multicenter 10-year cohort of children and adults. Altogether 152 patients (65 children and 87 adults) treated during the period 1980-1990 in three epilepsy centers were included and followed-up 2 years after surgery. Median age at onset of seizures was 4 years for the children and 12 years for the adults. A localization related epilepsy was present in 85% of the children and in 95% of the adults. The mean number of seizure types in the children was 1.7 (range 1-4) and in the adults 1.8 (range 1-4). The median monthly seizure frequency was 52 and 15 for children and adults respectively. Resective surgery was performed in 143 cases (94 temporal, 31 extratemporal, 9 multilobar and 9 major resection procedures) and palliative procedures in 16 cases (13 callosotomies and 3 stereotactic amygdalotomies). Postoperative neurological deficits were detected in 9% of the patients after temporal lobe resections and in 15% of the patients after extratemporal and multilobar resection procedures. Two years after resective surgery 53% of the children and 49% of the adults were seizure free. Another 25% of the patients had a more than 50% reduction of seizure frequency. In the postoperative non seizure free group of patients there was a negative correlation between decrease in weighted seizure severity and decrease in seizure frequency. This finding stresses the need for including other parameters than seizure frequency when evaluating the outcome of epilepsy surgery.