Predicting memory decline following epilepsy surgery: a multivariate approach

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Role of functional MRI in presurgical evaluation of memory function in temporal lobe epilepsy

Many diagnostic tools have been employed to predict the likelihood of a postoperative memory decline after a standard temporal lobectomy, including the intracarotid amobarbital testing (IAT) or Wada, regarded as the gold standard test for over the past half a century. Functional MRI (fMRI) is also a promising tool in that regard. Its routine use to predict the postoperative memory decline has been limited because of the varied study paradigms, discrepancies in analysis, and interpretation of the results. Based on the existing literatures, fMRI cannot replace IAT for the routine presurgical evaluation of the patients with temporal lobe epilepsy (TLE) yet. Large multicentre studies with a panel of memory test are required to determine the full potential of fMRI and use it reliably to replace IAT in the routine clinical practice. In this paper, we review various aspects of memory fMRI, including the experimental designs, data analysis, and findings.

Changes in memory function in children and young adults with temporal lobe epilepsy: a follow-up study

This longitudinal study explored change in memory function from childhood to young adulthood in temporal lobe epilepsy (TLE). The 24 participants (11 left TLE; 13 right TLE) had a mean age of 16.10 years (SD=4.13 years), and 14 had undergone surgery since initial assessment. Contrary to baseline, verbal memory deficits were lateralized (left<right on paired associate learning, p=.009, and delay, p=.02). Change over time interacted with laterality on a complex non-verbal memory task (p=.05), with the right but not the left group improving. A three-way time-by-laterality-by-surgery interaction was significant for delayed facial recognition (p=.05), with surgical groups improving irrespective of laterality. Non-surgical groups remained stable, although there was a trend for the right to improve and the left to decline. Results were independent of seizure variables, mood and IQ and suggest that memory in left TLE tends to remain stable over time and improve in right TLE.

Prediction of neuropsychological outcome after resection of temporal and extratemporal seizure foci

Resection of seizure foci is an effective treatment for the control of medically intractable epilepsy. However, cognitive morbidity can occur as a result of surgical intervention. This morbidity is dependent on several factors, including location and extent of resection, disease characteristics, patient demographic characteristics, and functional status of the tissue to be resected. In this review article, the authors provide a summary of the neurocognitive outcomes of epilepsy surgery with an emphasis on presurgical predictors of postsurgical cognitive decline.

Neuropsychology in temporal lobe epilepsy: influences from cognitive neuroscience and functional neuroimaging

Neuropsychologists assist in diagnosis (i.e., localization of dysfunction) and in prediction (i.e., how cognition may change following surgery) in individuals being considered for temporal lobe surgery. The current practice includes behavioural testing as well as mapping function via stimulation, inactivation, and (more recently) functional imaging. These methods have been providing valuable information in surgical planning for 60 years. Here, we discuss current assessment strategies and highlight how they are evolving, particularly with respect to integrating recent advances in cognitive neuroscience.

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

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

Postoperative neuropsychological outcome in patients with mesial temporal lobe epilepsy in Argentina

The aim of the present study is to compare pre- and postsurgical neuropsychological outcome in individuals suffering from mesial temporal lobe epilepsy (mTLE), in order to evaluate prognosis. The selected thirty-five patients had medically mTLE and had undergone an anterior temporal lobectomy (ATL). Neuropsychological evaluation was performed in three different stages: before ATL, 6 months after resection, and a year afterwards. Neuropsychological protocol evaluated attention, verbal memory, visual memory, executive function, language, intelligence, and handedness. There was a significant improvement (P = 0.030) in the group with visual memory deficit after surgery, whereas no changes were observed across patients with verbal memory deficit. No changes were observed in language after surgery. Executive function showed significant improvement 6 months after surgery (P = 0.035). Postoperative outcome of cognitive impairments depends on baseline neuropsychological status of the patients with TLE. In our case series, deficits found in patients with mTLE after ATL did not result in a subjective complaint.

Brain plasticity for verbal and visual memories in patients with mesial temporal lobe epilepsy and hippocampal sclerosis: an fMRI study

We aimed to identify the brain areas involved in verbal and visual memory processing in normal controls and patients with unilateral mesial temporal lobe epilepsy (MTLE) associated with unilateral hippocampal sclerosis (HS) by means of functional magnetic resonance imaging (fMRI). The sample comprised nine normal controls, eight patients with right MTLE, and nine patients with left MTLE. All subjects underwent fMRI with verbal and visual memory paradigms, consisting of encoding and immediate recall of 17 abstract words and 17 abstract drawings. A complex network including parietal, temporal, and frontal cortices seems to be involved in verbal memory encoding and retrieval in normal controls. Although similar areas of activation were identified in both patient groups, the extension of such activations was larger in the left-HS group. Patients with left HS also tended to exhibit more bilateral or right lateralized encoding related activations. This finding suggests a functional reorganization of verbal memory processing areas in these patients due to the failure of left MTL system. As regards visual memory encoding and retrieval, our findings support the hypothesis of a more diffuse and bilateral representation of this cognitive function in the brain. Compared to normal controls, encoding in the left-HS group recruited more widespread cortical areas, which were even more widespread in the right-HS group probably to compensate for their right mesial temporal dysfunction. In contrast, the right-HS group exhibited fewer activated areas during immediate recall than the other two groups, probably related to their greater difficulty in dealing with visual memory content.

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.

Connectivity between perisylvian and bilateral basal temporal cortices

Language processing requires the orchestrated action of different neuronal populations, and some studies suggest that the role of the basal temporal (BT) cortex in language processing is bilaterally distributed. Our aim was to demonstrate connectivity between perisylvian cortex and both BT areas. We recorded corticocortical evoked potentials (CCEPs) in 8 patients with subdural electrodes implanted for surgical evaluation of intractable epilepsy. Four patients had subdural grids over dominant perisylvian and BT areas, and 4 had electrode strips over both BT areas and left posterior superior temporal gyrus (LPSTG). After electrocortical mapping, patients with grids had 1-Hz stimulation of language areas. Patients with strips did not undergo mapping but had 1-Hz stimulation of the LPSTG. Posterior language area stimulation elicited CCEPs in ipsilateral BT cortex in 3/4 patients with left hemispheric grids. CCEPs were recorded in bilateral BT cortices in 3/4 patients with strips upon stimulation of the LPSTG, and in the LPSTG in the fourth patient upon stimulation of either BT area. This is the first in vivo demonstration of connectivity between LPSTG and both BT cortices. The role of BT cortex in language processing may be bilaterally distributed and related to linking visual information with phonological representations stored in the LPSTG.

Neuropsychological outcomes after epilepsy surgery: Systematic review and pooled estimates

PURPOSE

Epilepsy surgery is a safe surgical procedure, but it may be associated with cognitive changes. Estimates of the risk of decline in specific neuropsychological domains after epilepsy surgery would assist surgical decision making in clinical practice. The goal of this study was to conduct a systematic review to derive pooled estimates of the rate of losses and gains in neuropsychological functions after epilepsy surgery, using empirically based methods for quantifying cognitive change.

METHODS

An extensive literature search using PubMed, EmBase, and the Cochrane database was conducted, yielding 5,061 articles on epilepsy surgery, with 193 on neuropsychological outcomes (IQ, memory, language, executive functioning, attention, and subjective cognitive changes).

KEY FINDINGS

Of these, 23 met final eligibility criteria, with 22 studies involving temporal surgery only. Key aspects of inclusion criteria were N ≥ 20 and use of reliable change index or standardized regression-based change estimates. In addition to the proportion of patients experiencing losses and gains in each individual test, a single pooled estimate of gains and losses for each cognitive domain was derived using a random effects model. Weighted estimates indicated a risk to verbal memory with left-sided temporal surgery of 44%, twice as high as the rate for right-sided surgery (20%). Naming was reduced in 34% of left-sided temporal patients, with almost no patients with gains (4%). Pooled data on IQ, executive functioning, and attention indicated few patients show declines post surgery, but a substantial rate of improvement in verbal fluency with left-sided temporal surgery (27%) was found. Self-reported cognitive declines after epilepsy surgery were uncommon, and gains were reported in some domains where losses were found on objective tests (i.e., verbal memory and language). Variations in surgical techniques did not appear to have a large effect on cognitive outcomes, except for naming outcomes, which appeared better with more conservative resections. Sensitivity to postoperative changes differed across visual memory tests, but not verbal memory tests. Few conclusions could be made regarding cognitive risks and benefits of extratemporal epilepsy surgery, or of epilepsy surgery in children.

SIGNIFICANCE

In sum, epilepsy surgery is associated with specific cognitive changes, but may also improve cognition in some patients. The results provide base rate estimates of expected cognitive gains and losses associated with epilepsy surgery that may prove useful in clinical settings.

The neurobiology of cognitive disorders in temporal lobe epilepsy

Cognitive impairment, particularly memory disruption, is a major complicating feature of epilepsy. This Review will begin with a focus on the problem of memory impairment in temporal lobe epilepsy (TLE). We present a brief overview of anatomical substrates of memory disorders in TLE, followed by a discussion of how our understanding of these disorders has been improved by studying the outcomes of anterior temporal lobectomy. The clinical efforts made to predict which patients are at greatest risk of experiencing adverse cognitive outcomes following epilepsy surgery are also considered. Finally, we examine the vastly changing view of TLE, including findings demonstrating that anatomical abnormalities extend far outside the temporal lobe, and that cognitive impairments extend beyond memory function. Linkage between these distributed cognitive and anatomical abnormalities point to a new understanding of the anatomical architecture of cognitive impairment in epilepsy. Clarifying the origin of these cognitive and anatomical abnormalities, their progression over time and, most importantly, methods for protecting cognitive and brain health in epilepsy, present a challenge to neurologists.

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.

Presurgical epilepsy localization with interictal cerebral dysfunction

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

Intracarotid amobarbital procedure for epilepsy surgery

The intracarotid amobarbital procedure (IAP) has been used for more than half a century to determine language dominance and to assess risk for amnesia after anterior temporal lobectomy. However, because of the risk associated with angiography and the development of noninvasive techniques, the need for the IAP when evaluating patients for epilepsy surgery can now be questioned. The purpose of this review is to examine the clinical indications and efficacy of the Wada test in the preoperative evaluation of epilepsy surgery candidates. This article summarizes a debate that took place during the 2009 American Epilepsy Society (AES) annual course.

Mapping anterior temporal lobe language areas with fMRI: a multicenter normative study

Removal of the anterior temporal lobe (ATL) is an effective surgical treatment for intractable temporal lobe epilepsy but carries a risk of language and verbal memory deficits. Preoperative localization of functional zones in the ATL might help reduce these risks, yet fMRI protocols in current widespread use produce very little activation in this region. Based on recent evidence suggesting a role for the ATL in semantic integration, we designed an fMRI protocol comparing comprehension of brief narratives (Story task) with a semantically shallow control task involving serial arithmetic (Math task). The Story > Math contrast elicited strong activation throughout the ATL, lateral temporal lobe, and medial temporal lobe bilaterally in an initial cohort of 18 healthy participants. The task protocol was then implemented at 6 other imaging centers using identical methods. Data from a second cohort of participants scanned at these centers closely replicated the results from the initial cohort. The Story-Math protocol provides a reliable method for activation of surgical regions of interest in the ATL. The bilateral activation supports previous claims that conceptual processing involves both temporal lobes. Used in combination with language lateralization measures, reliable ATL activation maps may be useful for predicting cognitive outcome in ATL surgery, though the validity of this approach needs to be established in a prospective surgical series.

Beyond localization: the role of traditional neuropsychological tests in an age of imaging

Rapid advances in structural and functional magnetic resonance imaging (MRI) present two significant challenges to the rationale and role of the traditional neuropsychological assessment in the presurgical evaluation of epilepsy surgery candidates today. The first is a direct challenge to the model of material-specific memory that has underpinned much clinical practice over the last 50 years. The second, more fundamental, challenge goes to the very heart of the lateralizing/localizing approach that has been the cornerstone of clinical neuropsychology practice in epilepsy surgery centers to date. This review examines these challenges and suggests some ways in which the profession might respond and adapt. We conclude that noninvasive neuropsychological assessment remains a critical investigation in the presurgical evaluation of epilepsy surgery patients. Its value stretches beyond the localization of a surgically remediable seizure focus. Once a vital test, other investigations are now superior in this respect in many cases. However, new technologies have enhanced the role of the traditional neuropsychological assessment, which is now able to provide unparalleled insights and predictions into the way in which the underlying pathology, seizures, and proposed surgery shape an individual's profile of cognitive abilities. Detailed neuropsychological feedback enables the patient to make an informed decision, and forms the basis of the tailor made preemptive rehabilitation programs that can be implemented preoperatively, minimizing the most significant morbidity associated with epilepsy surgery today.

Imaging in the surgical treatment of epilepsy

Medically refractory focal epilepsy is potentially curable by surgery. This Review considers the application of recent advances in structural and functional brain imaging to increase the number of patients with epilepsy who are treated surgically, and to reduce the risk of complications arising from such intervention. Current optimal MRI of brain structure can identify previously undetectable lesions, with voxel-based and quantitative analyses further increasing the diagnostic yield. If MRI proves unremarkable, PET (with (18)F-fluorodeoxyglucose) and single-photon emission CT of ictal-interictal cerebral blood flow might identify the brain region that contains the epileptic focus. Magnetoencephalography plus simultaneous EEG and functional MRI can map the location of interictal epileptic discharges, thereby facilitating placement of intracranial recording electrodes to define the site of seizure onset. Functional MRI can also lateralize language and localize primary motor, somatosensory and language areas, and shows promise for predicting the effects of temporal lobe resection on memory. Tractography can visualize the main cerebral white matter tracts, thereby predicting and reducing surgery risk. Currently, displays of the optic radiation and pyramidal tracts are the most relevant for epilepsy surgery. Reliable integration of structural and functional data into surgical image-guidance systems is being pursued, and promises safer neurosurgery for epilepsy in the future.

Imaging memory in temporal lobe epilepsy: predicting the effects of temporal lobe resection

Functional magnetic resonance imaging can demonstrate the functional anatomy of cognitive processes. In patients with refractory temporal lobe epilepsy, evaluation of preoperative verbal and visual memory function is important as anterior temporal lobe resections may result in material specific memory impairment, typically verbal memory decline following left and visual memory decline after right anterior temporal lobe resection. This study aimed to investigate reorganization of memory functions in temporal lobe epilepsy and to determine whether preoperative memory functional magnetic resonance imaging may predict memory changes following anterior temporal lobe resection. We studied 72 patients with unilateral medial temporal lobe epilepsy (41 left) and 20 healthy controls. A functional magnetic resonance imaging memory encoding paradigm for pictures, words and faces was used testing verbal and visual memory in a single scanning session on a 3T magnetic resonance imaging scanner. Fifty-four patients subsequently underwent left (29) or right (25) anterior temporal lobe resection. Verbal and design learning were assessed before and 4 months after surgery. Event-related functional magnetic resonance imaging analysis revealed that in left temporal lobe epilepsy, greater left hippocampal activation for word encoding correlated with better verbal memory. In right temporal lobe epilepsy, greater right hippocampal activation for face encoding correlated with better visual memory. In left temporal lobe epilepsy, greater left than right anterior hippocampal activation on word encoding correlated with greater verbal memory decline after left anterior temporal lobe resection, while greater left than right posterior hippocampal activation correlated with better postoperative verbal memory outcome. In right temporal lobe epilepsy, greater right than left anterior hippocampal functional magnetic resonance imaging activation on face encoding predicted greater visual memory decline after right anterior temporal lobe resection, while greater right than left posterior hippocampal activation correlated with better visual memory outcome. Stepwise linear regression identified asymmetry of activation for encoding words and faces in the ipsilateral anterior medial temporal lobe as strongest predictors for postoperative verbal and visual memory decline. Activation asymmetry, language lateralization and performance on preoperative neuropsychological tests predicted clinically significant verbal memory decline in all patients who underwent left anterior temporal lobe resection, but were less able to predict visual memory decline after right anterior temporal lobe resection. Preoperative memory functional magnetic resonance imaging was the strongest predictor of verbal and visual memory decline following anterior temporal lobe resection. Preoperatively, verbal and visual memory function utilized the damaged, ipsilateral hippocampus and also the contralateral hippocampus. Memory function in the ipsilateral posterior hippocampus may contribute to better preservation of memory after surgery.

A comparison of two fMRI methods for predicting verbal memory decline after left temporal lobectomy: language lateralization versus hippocampal activation asymmetry

PURPOSE

Language lateralization measured by preoperative functional magnetic resonance imaging (fMRI) was shown recently to be predictive of verbal memory outcome in patients undergoing left anterior temporal lobe (L-ATL) resection. The aim of this study was to determine whether language lateralization or functional lateralization in the hippocampus is a better predictor of outcome in this setting.

METHODS

Thirty L-ATL patients underwent preoperative language fMRI, preoperative hippocampal fMRI using a scene encoding task, and pre- and postoperative neuropsychological testing. A group of 37 right ATL (R-ATL) surgery patients was included for comparison.

RESULTS

Verbal memory decline occurred in roughly half of the L-ATL patients. Preoperative language lateralization was correlated with postoperative verbal memory change. Hippocampal activation asymmetry was strongly related to side of seizure focus and to Wada memory asymmetry but was unrelated to verbal memory outcome.

DISCUSSION

Preoperative hippocampal activation asymmetry elicited by a scene encoding task is not predictive of verbal memory outcome. Risk of verbal memory decline is likely to be related to lateralization of material-specific verbal memory networks, which are more closely correlated with language lateralization than with overall asymmetry of episodic memory processes.

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.

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.

Hippocampal volumetry and functional MRI of memory in temporal lobe epilepsy

This study examined the utility of structural and functional MRI at 1.5 and 3T in the presurgical evaluation and prediction of postsurgical cognitive outcome in temporal lobe epilepsy (TLE). Forty-nine patients undergoing presurgical evaluation for temporal lobe (TL) resection and 25 control subjects were studied. Patients completed standard presurgical evaluations, including the intracarotid amobarbital test (IAT) and neuropsychological testing. During functional imaging, subjects performed a complex visual scene-encoding task. High-resolution structural MRI scans were used to quantify hippocampal volumes. Both structural and functional imaging successfully lateralized the seizure focus and correlated with IAT memory lateralization, with improvement for functional imaging at 3T as compared with 1.5 T. Ipsilateral structural and functional MRI data were related to cognitive outcome, and greater functional asymmetry was related to earlier age at onset. These findings support continued investigation of the utility of MRI and fMRI in the presurgical evaluation of TLE.

Intracarotid propofol testing: a comparative study with amobarbital

Twenty-five consecutive patients who underwent the Wada test using propofol as anesthetic were compared with 15 randomly selected patients who were tested using amobarbital. Time to verbal and nonverbal responses and time to motor power 3/5 did not differ between the two groups (P>0.05). The number of doses received by each patient and the percentage of patients needing more than one dose were significantly greater in the propofol group (P<0.005). Only one patient developed confusion, combativeness, and agitation. Despite the need for multiple doses, our patients had no residual drowsiness within 10 to 15 minutes of the propofol injection. This allowed us to perform the test on both sides on the same day separated only by 45 minutes. Propofol is an effective alternative to amobarbital in the Wada test, and may be used successfully in multiple repeated injections within the same test without significant residual sedation or significant adverse effects.

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.

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.

Preoperative fMRI predicts memory decline following anterior temporal lobe resection

BACKGROUND

Anterior temporal lobe resection (ATLR) benefits many patients with refractory temporal lobe epilepsy (TLE) but may be complicated by material specific memory impairments, typically of verbal memory following left ATLR, and non-verbal memory following right ATLR. Preoperative memory functional MRI (fMRI) may help in the prediction of these deficits.

OBJECTIVE

To assess the value of preoperative fMRI in the prediction of material specific memory deficits following both left- and right-sided ATLR.

METHODS

We report 15 patients with unilateral TLE undergoing ATLR; eight underwent dominant hemisphere ATLR and seven non-dominant ATLR. Patients performed an fMRI memory paradigm which examined the encoding of words, pictures and faces.

RESULTS

Individual patients with relatively greater ipsilateral compared with contralateral medial temporal lobe activation had greater memory decline following ATLR. This was the case for both verbal memory decline following dominant ATLR and for non-verbal memory decline following non-dominant ATLR. For verbal memory decline, activation within the dominant hippocampus was predictive of postoperative memory change whereas activation in the non-dominant hippocampus was not.

CONCLUSION

These findings suggest that preoperative memory fMRI may be a useful non-invasive predictor of postoperative memory change following ATLR and provide support for the functional adequacy theory of hippocampal function. They also suggest that fMRI may provide additional information, over that provided by neuropsychology, for use in the prediction of postoperative memory decline.

The impact of epilepsy surgery on cognition and behavior

Famous historical cases and current clinical experience clearly indicate that the success of epilepsy surgery cannot be judged with the basic algorithm "fewer seizures = better outcome." Many factors combine and entwine with the experience of medically intractable seizures to create associated patterns of behavior and cognition. Obtaining freedom from seizures does not automatically undo the historical tangle of these salient factors, many of which remain or are exacerbated after surgery. This review examines the preoperative, perioperative, and postoperative factors that influence postoperative cognition and behavior in adult patients with temporal lobe epilepsy. Consistent findings from group studies have long masked the considerable individual variations in cognitive and behavioral outcomes following surgery. Although more recent multivariate studies provide useful clinical data for prospective surgical candidates, comprehensive long-term follow-up studies are rare. We have certainly become more proficient at measuring both cognitive and behavioral outcomes following surgery, although the ecological validity of many follow-up measures, particularly in the cognitive domain, remains low. A reliance on test scores can mask significant differences in strategy, which can also be used as a sign of lateralized dysfunction. A shift away from the "can do versus can't do" approach to the assessment of cognitive strategies may hold the key to more meaningful pre- and postoperative cognitive assessments from the patient's perspective. Emergent functional imaging paradigms show much promise in this regard. A renewed focus on cognitive strategies may also be useful in planning postoperative rehabilitation programs. New directions for outcome research in epilepsy surgery are suggested with an emphasis on a patient-centered approach.

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.