The Role of the Intracarotid Amobarbital Procedure in Predicting Verbal Memory Decline after Temporal Lobe Resection

Wada test results contribute to the prediction of change in verbal learning and verbal memory function after temporal lobe epilepsy surgery

In recent years, the clinical usefulness of the Wada test (WT) has been debated among researchers in the field. Therefore, we aimed to assess its contribution to the prediction of change in verbal learning and verbal memory function after epilepsy surgery. Data from 56 patients with temporal lobe epilepsy who underwent WT and subsequent surgery were analyzed retrospectively. Additionally, a standard neuropsychological assessment evaluating attentional, learning and memory, visuospatial, language, and executive function was performed both before and 12 months after surgery. Hierarchical linear regression analyses were used to determine the incremental value of WT results over socio-demographic, clinical, and neuropsychological characteristics in predicting postsurgical change in patients' verbal learning and verbal memory function. The incorporation of WT results significantly improved the prediction models of postsurgical change in verbal learning (∆R2 = 0.233, p = .032) and verbal memory function (∆R2 = 0.386, p = .005). Presurgical performance and WT scores accounted for 41.8% of the variance in postsurgical change in verbal learning function, and 51.1% of the variance in postsurgical change in verbal memory function. Our findings confirm that WT results are of significant incremental value for the prediction of postsurgical change in verbal learning and verbal memory function. Thus, the WT contributes to determining the risks of epilepsy surgery and, therefore, remains an important part of the presurgical work-up of selected patients with clear clinical indications.

Beyond the Wada: An updated approach to pre-surgical language and memory testing: An updated review of available evaluation techniques and recommended workflow to limit Wada test use to essential clinical cases

The Intracarotid amobarbital test (IAT), also called Wada test, is considered the "gold standard" for lateralizing language dominance in the pre-surgical evaluation of patients with epilepsy. In addition, it has been further modified to assess the postoperative risk of amnesia in patients undergoing temporal lobectomy. Since then it has been utilized to lateralize language and assess pre-surgical memory function. Over the years, its popularity has declined due to several limitations and availability of alternative procedures like fMRI and MEG. A survey of its use in the pre-surgical evaluation for epilepsy surgery has not been performed since the 2008 international survey by Baxendale et al. and it was heavily skewed due to data from European and North American countries. Only approximately 12% of the epilepsy centers indicated that they used the Wada test in every patient to assess preoperative memory function and language lateralization before temporal lobectomy. Nowadays, we have many functional mapping tools at our disposal. It has become somewhat unsuitable to have epilepsy patients undergo an invasive test such as the Wada test for the risks associated with it outweigh the benefits. Our objective is to review the Wada Test and alternative methods of assessing language and memory dominance, as it is past its prime and should only be used in specific circumstances.

The clinical utility of a memory specialization index in epilepsy surgery patients with unilateral hippocampal sclerosis

OBJECTIVE

Although group studies provide some support for the material-specific model of memory function, there are considerable individual variations in memory function in people with temporal lobe epilepsy, even in those with the same underlying pathology. In this proof-of-concept study, we examined the sensitivity and specificity of a single measure of an individual's relative strength for the encoding of verbal or visual learning.

METHODS

Six hundred ninety-two patients with left hemisphere language dominance and unilateral hippocampal sclerosis completed verbal and visual encoding tasks with similar test structures as part of their presurgical evaluation. Three hundred one patients had right hippocampal sclerosis (RHS), and 391 patients had left hippocampal sclerosis (LHS). A memory specialization index (MSI) was calculated by subtracting the Visual Learning z-score from the Verbal Learning z-score. A positive value on the MSI indicates a relative strength in verbal learning. A negative score indicates a relative strength in visual learning.

RESULTS

Employing cut-offs of ±1, the MSI had a positive predictive value of 71% (confidence interval [CI] 95% 0.64-0.77) for LHS and 64% (CI 95% 0.55-0.74) for RHS and was superior to the standalone z-scores from the verbal and visual tests in each respect. In the LHS group, the MSI was significantly correlated with age and duration of epilepsy. Older patients who had a longer duration of epilepsy were more likely to demonstrate a similar level of impairment in both verbal and visual learning, with a decreasing discrepancy between the scores on the two tasks over time.

SIGNIFICANCE

Our MSI provides a measure with high specificity for RHS. The pattern of strengths and weaknesses in visual and verbal encoding may evolve with age and duration of epilepsy, and clinicians should be aware of these factors when interpreting the lateralizing significance of test scores, particularly in a presurgical setting.

Cognitive rehabilitation and prehabilitation in people with epilepsy

Epilepsy is now recognized as a network disorder of the brain that can impact cognition beyond the periictal disturbance associated with seizures. While there is a large literature on the assessment of cognitive functions, particularly memory, in people with epilepsy, there are far fewer studies looking at the efficacy of treatments for cognitive dysfunction in this population. Reviews of the cognitive rehabilitation literature in epilepsy have begun to outnumber original studies. This paper examines the possible reasons for this unsatisfactory ratio in the literature and examines the unique challenges and opportunities for cognitive rehabilitation in this population, with a particular focus on epilepsy surgical candidates. The concept of prehabilitation in this population is described. While traditional cognitive rehabilitation is implemented after a patient has developed a neuropsychological deficit, in surgical candidates, prehabilitation uses intact functions before they are lost to establish compensatory strategies and routines prior to surgery in preparation for postoperative changes. The likely postoperative neuropsychological profile for individual patients can now be modeled using preoperative data. These predictions can guide and inform the prehabilitation process. Rather than concluding with a generic call for more research, the paper presents a framework for a rehabilitation program with practical solutions to address cognitive difficulties in both surgical and nonsurgical populations of people with epilepsy.

Postoperative memory prognosis in temporal lobe epilepsy surgery: The contribution of postictal memory

OBJECTIVE

The prediction of verbal memory decline after temporal lobe epilepsy (TLE) surgery remains difficult at an individual level. We evaluated the prognostic value of postictal memory testing in predicting the postoperative verbal memory function.

METHODS

Sixty-three consecutive patients were included in the analysis who underwent TLE surgery at our center with preoperative interictal/postictal and postoperative memory testing. Verbal memory was evaluated using the Rey Auditory Verbal Learning Test (RAVLT). We used reliable change indices with 90% confidence interval (90% RCIs) to evaluate a significant postoperative memory decline. The sensitivity (Sn), specificity (Sp), positive predictive value (PPV), negative predictive value (NPV), area under the curve (AUC), and accuracy (ACC) were calculated. The analysis was performed for all TLE patients and for the subgroup with hippocampal sclerosis (HS).

RESULTS

Left-TLE patients (n = 31) had lower verbal memory scores on RAVLT than right-TLE at 3 months (57% vs 78%) and 12 months (53% vs 78%) after surgery. The 90% RCI was estimated to be a loss of 4 out of 15 items. The predictive value was Sn = 42%, Sp = 84%, PPV = 39%, NPV = 86%, AUC = 0.630, and ACC = 76% to predict a verbal memory decline in the whole group (n = 63). In HS patients (n = 41), the postictal verbal memory test had Sn = 50%, Sp = 88%, PPV = 50%, NPV = 88%, AUC = 0.689, and ACC = 81% to predict a significant postoperative decline.

SIGNIFICANCE

Postictal memory is a noninvasive bedside memory test that can help predict the postoperative verbal memory decline in patients with HS with an overall accuracy of 81%.

Comparing the Wada Test and Functional MRI for the Presurgical Evaluation of Memory in Temporal Lobe Epilepsy

PURPOSE OF REVIEW

The usefulness of the Wada test (WT) predicting memory impairment from temporal lobe epilepsy (TLE) surgery has been debated, and it has progressively been replaced by functional MRI (fMRI). We review the current role of WT and fMRI in the presurgical assessment of TLE, and how novel surgical techniques might improve cognitive outcomes.

RECENT FINDINGS

fMRI's ability to predict global amnesia has not been assessed. Although WT can produce false-positive results, it is still indicated in patients at risk for developing global amnesia: those with significant bilateral or contralateral memory deficits. In the current review, WT exhibited no added value, beyond preclinical data, for predicting material-specific memory impairment, whereas fMRI was reliable for either verbal or non-verbal memory decline. Abnormal functional connectivity on resting state fMRI (rs-fMRI) between the posterior cingulate and the hippocampus may be a predictor of postsurgical memory outcomes. Restricted resections to the pathogenic tissue, stereotactic laser, radiosurgery, and SEEG-guided thermos-coagulation were associated with better cognitive outcome. fMRI should be used routinely in the presurgical workup of TLE to predict verbal and/or non-verbal memory decline, whereas WT may be indicated when there is a high risk of postsurgical global amnesia. Rs-fMRI is a promising tool for the presurgical workup of TLE, and more restricted resections are recommended to enhance cognitive outcomes.

Electrical stimulation of the parahippocampal gyrus for prediction of posthippocampectomy verbal memory decline

OBJECTIVE Epilepsy surgery is of known benefit for drug-resistant temporal lobe epilepsy (TLE); however, a certain number of patients suffer significant decline in verbal memory after hippocampectomy. To prevent this disabling complication, a reliable test for predicting postoperative memory decline is greatly desired. Therefore, the authors assessed the value of electrical stimulation of the parahippocampal gyrus (PHG) as a provocation test of verbal memory decline after hippocampectomy on the dominant side. METHODS Eleven right-handed, Japanese-speaking patients with medically intractable left TLE participated in the study. Before surgery, they underwent provocative testing via electrical stimulation of the left PHG during a verbal encoding task. Their pre- and posthippocampectomy memory function was evaluated according to the Wechsler Memory Scale-Revised (WMS-R) and/or Mini-Mental State Examination (MMSE) before and 6 months after surgery. The relationship between postsurgical memory decline and results of the provocative test was evaluated. RESULTS Left hippocampectomy was performed in 7 of the 11 patients. In 3 patients with a positive provocative recognition test, verbal memory function, as assessed by the WMS-R, decreased after hippocampectomy, whereas in 4 patients with a negative provocative recognition test, verbal memory function, as assessed by the WMS-R or MMSE, was preserved. CONCLUSIONS Results of the present study suggest that electrical stimulation of the PHG is a reliable provocative test to predict posthippocampectomy verbal memory decline.

How neuropsychology can improve the care of individual patients with epilepsy. Looking back and into the future

Some of the roots of current clinical neuropsychology go back to the early days of epilepsy surgery. Looking back a huge number of publications have dealt with cognition in epilepsy. The major factors driving this work were questions relating to surgery, antiepileptic drugs and, more recently, also to underlying pathology. However, most factors affecting cognition in epilepsy have been discerned many years ago. The body of neuropsychological literature in this field has accumulated much knowledge, raising the question why, apart from epilepsy surgery settings, neuropsychology has still not been fully integrated in the routine care of patients with epilepsy. This review on the occasion of Seizure's 25th anniversary attempts to summarize clinically relevant diagnostic advances following a question guided, modular, and evidence-based approach. In doing so, we hope to attract the interest of readers to an exciting mode of assessment which does not only have theoretical but also practical relevance. The comorbidities of epilepsy are becoming an increasingly relevant topic. It is now widely accepted that, while epilepsy may be defined by the occurrence of epileptic seizures, these seizures represent only one of several possible sources of cognitive impairment. It is well-established that there are complex interactions between epilepsy, cognition and behavior, and that both seizures and problems with cognition or behavior may result from a common underlying pathology requiring treatment. With this review we aim to demonstrate that neuropsychology can make a highly valuable contribution to the care of individual patients by contributing to the diagnostic process and by serving as a tool for the monitoring of disease and treatment, thereby improving the quality and safety of patient care. On a national, European, and international level, first efforts are being made to homogenize diagnostics across epilepsy centers and countries in order to achieve a common language and core standards. This should improve communication within and outside the speciality, and help to generate the data required to allow the field to make further progress.

Hippocampal Transections for Epilepsy

Multiple hippocampal transection (MHT) is a novel surgical procedure that serves to disrupt seizure propagation fibers within the hippocampus without impairing verbal memory or the loss of stem cells. Given the paucity of literature regarding the utility and long-term outcome of MHT, a review is presented of the current literature to support the utility of this procedure in the treatment of intractable temporal lobe epilepsy. Long-term outcome analysis of this technique has been reported by 2 independent groups. Both groups used intraoperative electrocorticography. All patients underwent multiple subpial transection on the neocortex and MHT on the hippocampus.

Influence of anxiety on memory performance in temporal lobe epilepsy

This study examined the degree to which anxiety contributed to inconsistent material-specific memory difficulties among 243 patients with temporal lobe epilepsy from the Multisite Epilepsy Study. Visual memory performance on the Rey Complex Figure Test (RCFT) was poorer for those with high versus low levels of anxiety but was not found to be related to the TLE side. The verbal memory score on the California Verbal Learning Test (CVLT) was significantly lower for patients with left-sided TLE than for patients with right-sided TLE with low anxiety levels but equally impaired for those with high anxiety levels. These results suggest that we can place more confidence in the ability of verbal memory tests like the CVLT to lateralize to left-sided TLE for those with low anxiety levels, but that verbal memory will be less likely to produce lateralizing information for those with high anxiety levels. This suggests that more caution is needed when interpreting verbal memory tests for those with high anxiety levels. These results indicated that RCFT performance was significantly affected by anxiety and did not lateralize to either side, regardless of anxiety levels. This study adds to the existing literature which suggests that drawing-based visual memory tests do not lateralize among patients with TLE, regardless of anxiety levels.

Using multivariate data reduction to predict postsurgery memory decline in patients with mesial temporal lobe epilepsy

Predicting postsurgery memory decline is crucial to clinical decision-making for individuals with mesial temporal lobe epilepsy (mTLE) who are candidates for temporal lobe excisions. Extensive neuropsychological testing is critical to assess risk, but the numerous test scores it produces can make deriving a formal prediction of cognitive change quite complex. In order to benefit from the information contained in comprehensive memory assessment, we used principal component analysis (PCA) to simplify neuropsychological test scores (presurgical and pre- to postsurgical change) obtained from a cohort of 56 patients with mTLE into a few easily interpretable latent components. We next performed discriminant analyses using presurgery latent components to categorize seizure laterality and then regression analyses to assess how well presurgery latent components could predict postsurgery memory decline. Finally, we validated the predictive power of these regression models in an independent sample of 18 patients with mTLE. Principal component analysis identified three significant latent components that reflected IQ, verbal memory, and visuospatial memory, respectively. Together, the presurgery verbal and visuospatial memory components classified 80% of patients with mTLE correctly according to their seizure laterality. Furthermore, the presurgery verbal memory component predicted postsurgery verbal memory decline, while the presurgery visuospatial memory component predicted visuospatial memory decline. These regression models also predicted postsurgery memory decline successfully in the independent cohort of patients with mTLE. Our results demonstrate the value of data reduction techniques in identifying cognitive metrics that can characterize laterality of damage and risk of postoperative decline.

Hemispheric lateralization interrupted: material-specific memory deficits in temporal lobe epilepsy

The hemispheric lateralization of memory has largely been informed through the study of patients with temporal lobe epilepsy originating from medial temporal sources (mTLE). The material-specific model of memory relies on the basic framework that the left temporal lobe mediates verbal memories, while the right temporal lobe mediates non-verbal memories. Over the years, this model has been refined, and even challenged, as our understanding of the material-specific memory deficits in mTLE has been further elaborated in the neuropsychological and neuroimaging literature. The first goal of this mini-review is to highlight the major findings in the mTLE literature that have advanced and expanded our understanding of material-specific memory deficits in mTLE. Second, we will review how functional neuroimaging patterns of material-specific hemispheric lateralization in mTLE are being translated into the innovative clinical application of preoperative fMRI memory mapping.

Cognitive outcome after stereotactic amygdalohippocampectomy

PURPOSE

We sought to determine the neuropsychological outcome after stereotactic radiofrequency amygdalohippocampectomy performed for intractable mesial temporal lobe epilepsy.

METHODS

The article describes the cases of 31 patients who were evaluated using the Wechsler Adult Intelligence Scale-Revised and the Wechsler Memory Scale-Revised prior to, and one year after, surgery.

KEY FINDINGS

Patients showed increases in their mean Full Scale, Verbal and Performance IQ scores of 4, 3 and 4 IQ points respectively (p<.05). 5 (17.2%), 4 (13.8%) and 4 (13.3%) patients improved in their Full-scale, Verbal and Performance IQ respectively. No significant changes were found in memory performance - with a mean increase of 1, 3 and 0 MQ points in Global, Verbal and Visual memory respectively (p<.05). Global memory improved in 3 (10.3%) patients, verbal memory in 1 (3.4%) and 1 patient (3.3%) showed deterioration in visual memory.

SIGNIFICANCE

Our results provide evidence for unchanged memory in patients with MTLE after the procedure. No verbal memory deterioration was detected in any of our patients, while improvements were found in intellectual performance. The results suggest that stereotactic radiofrequency amygdalahippocampectomy could be superior to open surgery in terms of its neurocognitive outcomes. A larger randomised trial of these approaches is justified.

Preoperative prediction of verbal episodic memory outcome using FMRI

This article focuses on an important neurosurgical problem for which functional imaging may have a role. Temporal lobe epilepsy surgery typically involves removal of much of the anterior medial temporal lobe, which is critical for encoding and retrieval of long-term episodic memories. Verbal episodic memory decline after left anterior temporal lobe resection occurs in 30% to 60% of such patients. Recent studies show that preoperative fMRI can predict the degree of verbal memory change that will occur, and that fMRI improves prediction accuracy when combined with other routine tests. The predictive power of fMRI appears to be at least as good as the Wada memory test, making fMRI a viable noninvasive alternative to the Wada for preoperative assessment.

Nonresective hippocampal surgery for epilepsy

INTRODUCTION

Clinical experience with a new surgical procedure called multiple hippocampal transections is described. In this procedure, seizure circuits within the hippocampus are disrupted by making multiple cuts parallel to the hippocampal digitations; while the vertical functional fibers are preserved.

METHODS

Ten patients with temporal lobe epilepsy are described. The male/female ratio is 6:4, the ages of the patients were 20-53 years, and follow-up periods were 10-34 months, with a median of 21 months. Five patients had no hippocampal sclerosis, two had minimal sclerosis, and three had significant sclerosis. Six patients had surgery on the dominant side and five had failed the Wada test. Multiple hippocampal transections were made at 4-mm intervals. The neocortex was then treated with multiple subpial transections. In addition, six patients had resections of the temporal tip.

RESULTS

There were no permanent neurologic complications: seven patients are seizure-free, two have rare seizures, and one has 60% decrease in seizure frequency. Eight patients had both pre- and postoperative memory testing. Among these eight patients, five had improved verbal memory, three had improved visual memory, and three had a slight drop in visual memory.

CONCLUSION

This is a small series with a short follow-up period. However, the results are encouraging enough to warrant further trials. In addition, this may be an effective alternative procedure for those who fail the Wada test and do not have significant temporal lobe sclerosis or who have seizures originating from the dominant side.

Functional MRI is a valid noninvasive alternative to Wada testing

Partial removal of the anterior temporal lobe (ATL) is a highly effective surgical treatment for intractable temporal lobe epilepsy, yet roughly half of patients who undergo left ATL resection show a decline in language or verbal memory function postoperatively. Two recent studies demonstrate that preoperative fMRI can predict postoperative naming and verbal memory changes in such patients. Most importantly, fMRI significantly improves the accuracy of prediction relative to other noninvasive measures used alone. Addition of language and memory lateralization data from the intracarotid amobarbital (Wada) test did not improve prediction accuracy in these studies. Thus, fMRI provides patients and practitioners with a safe, noninvasive, and well-validated tool for making better-informed decisions regarding elective surgery based on a quantitative assessment of cognitive risk.

Postoperative memory prediction in left temporal lobe epilepsy: the Wada test is of no added value to preoperative neuropsychological assessment and MRI

The contribution of the Wada test (intracarotid amytal procedure, IAP) to predicting postoperative memory outcome in left temporal lobe epilepsy (LTLE) is becoming increasingly controversial when preoperative neuropsychological evaluation and MRI findings are available. We retrospectively analyzed 59 patients with LTLE who underwent en bloc temporal lobe resection. All patients had valid bilateral IAP test results, complete pre- and postoperative neuropsychological evaluation, and MRI grading on a 5-point scale integrating T 2 signal increase and degree of atrophy. Thirty percent of patients showed postoperative memory decline. Multiple regression analysis revealed that significant predictors of decline [F(2.56)=22.71, P<0.001, r(2)=0.448] included preoperative memory learning score [t=-5.89, P<0.001] and MRI classification [t=3.10, P<0.003], but not IAP scores. The IAP is of no added value in the prediction of postoperative memory outcome in LTLE in the presence of comprehensive neuropsychological and MRI data.

The intracarotid amobarbital or Wada test: unilateral or bilateral?

OBJECTIVE

In the Netherlands, presurgical screening for temporal lobe epilepsy (TLE) includes the intracarotid amobarbital procedure (IAP), consisting of two consecutive injections of amobarbital, ipsilateral and contralateral to the epileptic focus. We studied whether a bilateral IAP has added value to a unilateral, ipsilateral IAP.

METHODS

This population-based study included 183 consecutive patients referred for screening for TLE surgery who underwent bilateral IAP. Using multivariable modeling, we assessed the added value of bilateral IAP on the decision for surgery, resection size, amygdalohippocampectomy, post-operative seizure freedom, memory performance, and IQ change.

RESULTS

Given the results from the unilateral IAP, the bilateral IAP had added prognostic value for postoperative change in verbal memory (P < 0.01) and verbal IQ (P < 0.01), especially if patients had a left-sided focus. In contrast, information provided by the contralateral IAP was not associated with decision-making or surgical strategy.

CONCLUSIONS

A bilateral IAP has added value in predicting post-operative verbal memory and IQ. A bilateral IAP is currently not used to guide surgical strategy, but may be used for this purpose when verbal capacity is of particular concern in patients with a left-sided focus. In other cases, IAP is best performed unilaterally.

Verbal memory in mesial temporal lobe epilepsy: beyond material specificity

The idea that verbal and non-verbal forms of memory are segregated in their entirety, and localized to the left and right hippocampi, is arguably the most influential concept in the neuropsychology of temporal lobe epilepsy, forming a cornerstone of pre-surgical decision making, and a frame for interpreting postoperative outcome. This critical review begins by examining some of the unexpressed but inescapable assumptions of the material-specificity model: (i) verbal and non-verbal memory are unitary and internally homogenous constructs; and (ii) left and right memory systems are assumed to be independent, self-contained modules. The next section traces the origins of an alternative view, emanating largely from three challenges to these assumptions: (i) verbal memory is systematically fractionated by left mesial temporal foci; (ii) the resulting components are differentially localized within the left temporal lobe; and (iii) verbal and non-verbal memory functions are not entirely lateralized. It is argued here that the perirhinal cortex is a key node in a more extensive network mediating protosemantic associative memory. Impairment of this fundamental memory system is a proximal neurocognitive marker of mesial temporal epileptogenesis.

Stimulus type affects Wada memory performance

The effects of amytal injection side, seizure focus laterality, and stimulus type (real and line-drawn objects, printed words, and faces) on recognition memory were studied during the Wada procedure. To-be-remembered stimuli were presented during cerebral anesthesia to 35 patients with left temporal lobe epilepsy (LTLE) and 28 patients with right temporal lobe epilepsy (RTLE), all with left hemisphere language dominance. In both groups, recognition of real and line-drawn objects was best after anesthetization of the lesional hemisphere. Recognition of faces was poor after either injection in patients with RTLE, but only after right injection in patients with LTLE. Conversely, recognition of words by patients with LTLE was impaired equally after either injection, but more so after left than right injection in patients with RTLE. The findings suggest that (1) real and line-drawn objects are "dually encoded" and memory accuracy depends on seizure focus laterality, and (2) accuracy in recognition of words and faces is related to seizure focus laterality, but may also depend on the language dominance of the hemisphere being assessed.

The Wada test in Austrian, Dutch, German, and Swiss epilepsy centers from 2000 to 2005: a review of 1421 procedures

Twenty-six Austrian, Dutch, German, and Swiss epilepsy centers were asked to report on use of the Wada test (intracarotid amobarbital procedure, IAP) from 2000 to 2005 and to give their opinion regarding its role in the presurgical diagnosis of epilepsy. Sixteen of the 23 centers providing information had performed 1421 Wada tests, predominantly the classic bilateral procedure (73%). A slight nonsignificant decrease over time in Wada test frequency, despite slightly increasing numbers of resective procedures, could be observed. Complication rates were relatively low (1.09%; 0.36% with permanent deficit). Test protocols were similar even though no universal standard protocol exists. Clinicians rated the Wada test as having good reliability and validity for language determination, whereas they questioned its reliability and validity for memory lateralization. Several noninvasive functional imaging techniques are already in use. However, clinicians currently do not want to rely solely on noninvasive functional imaging in all patients.

Epilepsy surgery: eligibility criteria and presurgical evaluation

Epilepsy surgery has benefited from major advances during the last 20 years, thanks to the development of neuroimaging and long-term video-electroencephalographic (EEG) monitoring. However, it remains the case that only a small minority of potential epilepsy surgery candidates will have access to a comprehensive presurgical evaluation. Furthermore, this subset of patients are operated on after an average of 20 to 25 years of epilepsy duration. Among the various reasons that prevent many patients from benefiting from a timely presurgical evaluation, we need to emphasize the role of inaccurate information regarding eligibility criteria and lack of standardized practice. This review aims at providing an indepth discussion of the current views regarding the definition of surgical candidates, and the role of the numerous investigations used in the presurgical evaluation of patients with drug-resistant epilepsy.

The eligibility criteria required to enter a presurgical evaluation in 2008 should be relatively liberal, provided that the patient suffers from disabling seizures unrelated to an idiopathic generalized epileptic syndrome, despite appropriate antiepileptic drug treatment However, the decision as to whether or not to perform a presurgical evaluation must be individualized, and take into account the likelihood of meeting the patient's expectations in terms of outcome. These expectations need to be balanced with the apparent severity of the epileptic condition, the chance of achieving a successful surgical treatment, and the risk of a postoperative neurological, cognitive, or psychiatric deterioration. The roles and specific features of the main types of presurgical investigations are reviewed.

Use of preoperative functional MRI to predict verbal memory decline after temporal lobe epilepsy surgery

PURPOSE

Verbal memory decline is a frequent complication of left anterior temporal lobectomy (L-ATL). The goal of this study was to determine whether preoperative language mapping using functional magnetic resonance imaging (fMRI) is useful for predicting which patients are likely to experience verbal memory decline after L-ATL.

METHODS

Sixty L-ATL patients underwent preoperative language mapping with fMRI, preoperative intracarotid amobarbital (Wada) testing for language and memory lateralization, and pre- and postoperative neuropsychological testing. Demographic, historical, neuropsychological, and imaging variables were examined for their ability to predict pre- to postoperative memory change.

RESULTS

Verbal memory decline occurred in over 30% of patients. Good preoperative performance, late age at onset of epilepsy, left dominance on fMRI, and left dominance on the Wada test were each predictive of memory decline. Preoperative performance and age at onset together accounted for roughly 50% of the variance in memory outcome (p < 0.001), and fMRI explained an additional 10% of this variance (p <or= 0.003). Neither Wada memory asymmetry nor Wada language asymmetry added additional predictive power beyond these noninvasive measures.

DISCUSSION

Preoperative fMRI is useful for identifying patients at high risk for verbal memory decline prior to L-ATL surgery. Lateralization of language is correlated with lateralization of verbal memory, whereas Wada memory testing is either insufficiently reliable or insufficiently material-specific to accurately localize verbal memory processes.

The selective amobarbital test in the anterior choroidal artery: perfusion pattern assessed by intraarterial SPECT and prediction of postoperative verbal memory

To screen for patients at risk for memory decline after temporal lobe epilepsy (TLE) surgery, selective amobarbital procedures, such as injection into the anterior choroidal artery (ACA-IAT), are sometimes used. We investigated the extent of the territory affected during ACA-IAT and its predictive value with respect to postoperative memory. Seventeen patients with TLE underwent ACA-IAT. In 9 of 17 patients, intraarterial SPECT co-registrated to MRI allowed delineation of amobarbital-perfused structures. Another subgroup of 9 of 17 patients underwent anterior temporal lobectomy. Verbal memory was tested pre- and postoperatively and during ACA-IAT. Major variations in the ACA-IAT perfusion pattern occurred and were not correlated with the verbal memory scores during ACA-IAT. Postoperatively, no patient experienced a severe verbal memory decline, but individual postoperative performance was not correlated with results during ACA-IAT. Our study suggests that ACA-IAT can be used to screen for severe postoperative amnesia in inconclusive cases, but cannot predict individual outcome, even when the perfusion pattern is taken into account.