MRI hippocampal volumes and memory function before and after temporal lobectomy

Quantitative magnetic resonance imaging in consecutive patients evaluated for surgical treatment of temporal lobe epilepsy

We present the results of quantitative Magnetic Resonance Imaging (MRI) in 55 consecutively referred patients with clinical evidence of temporal lobe epilepsy (TLE). The Cavalieri method was used in combination with point counting to provide unbiased estimates of the volume of the left and right hippocampus, amygdala, temporal lobe, lateral ventricles and cerebral hemisphere, and pixel by pixel maps of the T2 relaxation time were computed for both central and anterior sections of the hippocampus. The 99th centiles of hippocampal volume, hippocampal volume asymmetry and T2 relaxation times in 20 control subjects provided limits which identified the presence of MTS. The results of the quantitative MRI were compared with the results of conventional diagnostic MRI, foramen ovale (FO) recording and the WADA test. Thirty-one patients were found to have unilateral MTS (17 left and 14 right) and 7 bilateral MTS. No evidence of MTS was detected in 16 patients. Of the 31 patients diagnosed with unilateral MTS on the basis of hippocampal volume and T2 measurement, 74% and 77% would respectively have received the same diagnosis on the basis of hippocampal volume and T2 measurements alone. In comparison to FO recording, quantitative MRI has a sensitivity of 55% and a specificity of 86%, while conventional diagnostic MRI has a sensitivity of 42% and a specificity of 80% for detection of MTS. Unilateral abnormalities were detected by FO recording in 30% cent of patients who appeared normal on quantitative MRI. WADA test results were available for 40 patients. The findings were consistent with quantitative MRI showing reduced memory function ipsilateral to unilateral MTS in 18 patients, but reduced memory function contralateral to unilateral MTS in two patients, and reduced memory function without MR abnormality in seven patients. WADA testing revealed unilateral memory impairments where MRI found bilateral pathology in 4 patients and in 4 patients in whom quantitative MRI detected unilateral MTS there was no evidence of reduced memory during WADA testing of the corresponding cerebral hemisphere. In the patients with unilateral right MTS a highly significant negative correlation (p = 0.0003) was observed between age of onset and the volume of the contralateral temporal lobe. Quantitative MR imaging of the hippocampus (i.e. volume and T2 measurement) is preferable to conventional radiological reporting for providing objective evidence of the presence of MTS on which to base the referral of patients for surgery, and since it has associated morbidity FO recording is now only being used in selected patients. Furthermore, stereology provides a convenient method for estimating the volume of other brain structures, which is relevant to obtaining a better understanding of the effects of laterality and age of onset of TLE.

Pediatric epilepsy surgery: neuroimaging, neuropsychology, and anticonvulsants

Neuroimaging and the neuropsychological evaluation are important components of the presurgical evaluation for epilepsy surgery. Advances in neuroimaging over the last decade, to a large part, underlie improvements in pediatric epilepsy surgery outcomes. The neuropsychological evaluation plays an important role in the evaluation of the older child and adolescent, particularly in the evaluation of mesial temporal sclerosis. However, its role in the young child being considered for surgery remains to be defined. This section reviews the definition of medical intractability, issues related to medication withdrawal during video-EEG monitoring, recent neuroimaging advances, and the neuropsychological evaluation.

Intracarotid amobarbital procedure and prediction of postoperative memory in patients with left temporal lobe epilepsy and hippocampal sclerosis

PURPOSE

Although temporal lobe epilepsy (TLE) patients with dominant hemisphere hippocampal sclerosis generally have good cognitive outcome after anterior temporal lobectomy (ATL), a minority of patients experience at least mild post-ATL decline on one or more standardized measures of episodic and semantic memory. The goal of this investigation was to determine whether memory outcome in this group could be predicted from preoperative intracarotid amobarbital procedure (IAP) recognition memory scores.

METHODS

Data from 22 left TLE patients were studied retrospectively. All were left hemisphere language dominant and had IAP scores for each hemisphere, a significant degree of pathology-confirmed left hippocampal sclerosis (HS+), and no positive MRI findings other than atrophy. Cognitive outcome status was represented by the number of pre- to post-ATL declines across three tests, as defined by 90th percentile Reliable Change Index (RCI) criteria.

RESULTS

Only 14% of the sample exhibited decline on more than one memory test. Low right IAP (left hemisphere injection) scores and relatively high preoperative cognitive ability and age at surgery predicted a greater risk of post-ATL memory decline.

CONCLUSIONS

A minority of left TLE HS+ patients experience at least a mild degree of RCI-defined decline in episodic or semantic memory after ATL. The right hemisphere IAP memory score, which reflects the functional reserve of the contralateral hemisphere, can help predict the risk of postoperative memory decline for TLE patients in whom HS+ is likely based on the presence of hippocampal atrophy on MRI or early age of seizure onset.

Postoperative hippocampal remnant shrinkage and memory decline: a dynamic process

BACKGROUND

The severity of postoperative memory decline in unilateral temporal lobectomy patients has been associated both with the extent of hippocampal resection and MRI measures of preoperative hippocampal volume. Serial MRI of the hippocampal remnant suggest that further volume loss occurs in the immediate postoperative period. For the majority of patients, this process appears to stabilize within the first 3 months. The authors examined the relationship between the dynamic volume of the hippocampal remnant and postoperative memory decline.

METHOD

Seventeen adult temporal lobectomy patients (nine, left; eight, right) underwent a full neuropsychological assessment and a volumetric MRI scan preoperatively and 3 months postoperatively. Examination of the posterior hippocampal remnant on the postoperative scan revealed volume loss in this segment compared to the identical segment preoperatively in 16 of 17 cases. Spearman's correlations were used to examine the relationship between postoperative memory decline (postoperative - preoperative memory scores) and the postoperative/preoperative hippocampal remnant volume ratio.

RESULTS

The volume of the hippocampal remnant left in situ was significantly correlated with postoperative memory change. Patients with smaller remnant volumes demonstrated more postoperative memory decline than those with larger remnants. In addition, extensive hippocampal remnant shrinkage was associated with postoperative memory decline in both the right and left temporal lobectomy groups.

CONCLUSIONS

The absolute volume and subsequent volume loss in the hippocampal remnant following surgery can influence postoperative memory change. These findings suggest that postoperative processes should be considered in addition to preoperative pathology and surgical factors in the prediction of postoperative memory change.

Diagnosis of Alzheimer's disease: MRI of the hippocampus vs delayed recall

Hippocampal volume measurements using magnetic resonance imaging (MRI) and assessment of performance in tests of delayed recall are among the most useful aids for diagnosing early Alzheimer's disease (AD) on an individual level. However, their comparative diagnostic accuracy has not been previously addressed. In this study we compared the diagnostic accuracy of these two methods in 57 patients with probable AD according to the NINCDS-ADRDA criteria, and 34 age- and gender-matched control subjects. The discriminatory power of the hippocampal volumes and delayed recall performance, Russel's Adaptation of the Visual Reproduction Test (VRT), were compared in discrimination function and receiver operator characteristic analyses. Right and left hippocampal volumes resulted in correct classification of 85.7-86.8% of the study subjects, respectively, while performance in the VRT resulted in correct classification of 93.4% of subjects. The area under curve value was 0.93 for the left hippocampus and 0.96 for the VRT. These data suggest that assessment of delayed recall with the VRT is of high diagnostic accuracy, and may surpass the diagnostic accuracy of hippocampal volumetry.

Nonlinear Trends in Hippocampal Metabolic Function and Verbal Memory: Evidence of Cognitive Reserve in Temporal Lobe Epilepsy?

The present study explored the possibility of nonlinear trends in the relationship between verbal memory and hippocampal function in a series of 33 patients with temporal lobe epilepsy (TLE). Right and left hippocampal metabolic function was quantified using levels of hippocampal creatine to N-acetylaspartate (Cr/NAA) derived from (1)H magnetic resonance spectroscopic imaging. An exploratory neural network analysis (multi-layer perceptron) suggested the possibility of either a quadratic or cubic trend in the relationship between left hippocampal Cr/NAA and verbal retention. Using regression-based curve estimation, the cubic function was found to optimally fit the data, explaining 41% of the variance in the relationship between verbal memory and hippocampal metabolic function. This was contrasted to the 28% variance explained by simple linear regression. These findings suggest that (1) the relationship between verbal retention and hippocampal function in patients with TLE is nonlinear, and (2) this could be explained in terms of a possible "cognitive reserve." Clinical implications are discussed.

Beyond speech lateralization: a review of the variability, reliability, and validity of the intracarotid amobarbital procedure and its nonlanguage uses in epilepsy surgery candidates

While the intracarotid amobarbital procedure (IAP) was originally utilized to lateralize speech functions as an aid in the surgical treatment of epilepsy, additional uses for the IAP have emerged including: (1) the use of the IAP to predict post-surgical memory changes, including both global amnesia and smaller, yet significant, material-specific memory deficits; (2) the use of the IAP to provide confirmatory evidence of lateralization of seizure focus; and (3) the use of the IAP to predict post-surgical relief from seizures. While the literature on the IAP is extensive and growing, its utility is marred by the wide variability associated with the procedure itself from epilepsy center to center. This variability renders comparisons among IAP studies problematic and conclusions about IAP efficacy difficult. The variability associated with the amobarbital procedures, as well as the reliability and the validity of the IAP in its nonlanguage uses is reviewed here. A special emphasis is devoted to research conducted in the last decade. Also discussed is the future of the IAP including anticipated research directions.

Occurrence of hippocampal sclerosis: is one hemisphere or gender more vulnerable?

PURPOSE

We analyzed a large group of patients investigated for suspected seizures to test whether gender or side are important factors in the origins of hippocampal sclerosis (HS).

METHODS

We studied 996 consecutive patients (48% men, 52% women) by using standard hippocampal T2-relaxometry methods.

RESULTS

HS was associated with a highly abnormal T2 time (< or =113 ms). Categoric analysis showed that hippocampal T2 time was independent of gender and side. T2 time was bilaterally normal in 81% of men and in 79% of women; it was unilaterally abnormal in 15% of both men and women; and bilaterally abnormal in 4% of men and in 6% of women. Highly abnormal T2 relaxometry, suggesting HS, occurred with equal frequency in men and women and on the right and left sides. Quantitative analysis of hippocampal T2 times showed values not differing significantly between men and women or between the right and left hemispheres. There was no significant interaction between gender and side.

CONCLUSIONS

In patients with seizure disorders, hippocampal T2 relaxometry is not different in adult men and women and in the right and left hemispheres.

Combined measurements of hippocampal N-acetyl-aspartate and T2 relaxation time in the evaluation of mesial temporal lobe epilepsy: correlation with clinical severity and memory performances

PURPOSE

In this study we tried to find a correlation between the clinical severity and memory performances, by comparing proton magnetic resonance (MR) spectroscopy and T2 relaxation time measurements in the hippocampi, in a homogeneous group of 27 patients with unilateral mesial temporal lobe epilepsy with ipsilateral hippocampal sclerosis on MR imaging, with a view to answer the following questions: (a) how sensitive is this approach for the assessment of the apparently normal contralateral hippocampus, (b) do the results relate to the clinical severity, and (c) does it allow evaluation of the degree of hippocampal dysfunction.

METHODS

Volume-selective proton MR spectroscopy of the head of both hippocampi was performed at 3 T, by using the PRESS sequence, with an echo time of 135 ms, to estimate NAA/(Cho + Cr) ratios. The relaxation times were measured at 0.28 T, by using a conventional Carr-Purcell-Meiboom-Gill sequence, with a repetition time of 2,000 ms, an echo time of 15 ms, and 48 echoes.

RESULTS

The combination of NAA/(Cho + Cr) ratio and T2 relaxation time values was allowed to classify contralateral hippocampus abnormalities in two groups: first, decreased NAA/(Cho + Cr) ratio with strongly increased T2 relaxation time values corresponding to abnormalities observed in sclerotic ipsilateral hippocampi; and second, decreased NAA/(Cho + Cr) ratio with normal or slightly increased T2 relaxation time values. Whereas the NAA/(Cho + Cr) ratio or T2 relaxation time value alone was not correlated with memory performances, their association shows that left hippocampal injury evaluated both by NAA and T2 relaxation time measurements was clearly correlated with verbal memory scores, and right hippocampal injury, with visual memory scores. On the other hand, the maximal seizure frequency reported by the patients was correlated with ipsilateral NAA/(Cho + Cr) ratio and T2 relaxation time values but not with contralateral results.

CONCLUSIONS

We showed that the combination of NAA and T2 relaxation time measurements can be used to examine the degree of ipsi- and contralateral hippocampal dysfunction or injuries and their relations with memory performances in the presurgical evaluation of patients.

Normierungsstudie zum Verbalen Lern- und Merkfähigkeitstest (VLMT)

Zusammenfassung. Der Verbale Lern- und Merkfähigkeitstest (VLMT) ( Helmstaedter & Durwen, 1990 ), die deutsche Form des Auditory Verbal Learning Test (AVLT) ( Lezak, 1983 ), ist ein Wortlistenlernparadigma, mit dem mehrere Gedächtnisparameter auf ökonomische Weise in einer Testung erfaßt werden können. In Ergänzung zu einer erst kürzlich an Kindern durchgeführten Studie ( Schweisthal, 1997 ) liefert die vorliegende Untersuchung Normdaten für den VLMT, die an 221 gesunden Personen im Alter von 15-45 Jahren erhoben wurden. Die unterschiedlichen Gedächtnisparameter wurden auf ihre Abhängigkeit von den Variablen Geschlecht, Alter und verbaler kristalliner Intelligenz geprüft. Nur zwischen den Jüngeren (15-30 Jahre: n = 157) und den Älteren (31-45 Jahre: n = 64) fanden sich Unterschiede in der Supraspanne, der Lernleistung und der Wiedererkennensleistung. Daher wurden für diese Parameter altersabhängige Normen berechnet. Diese gewährleisten angesichts der Relevanz von Wortlistenlernparadigmen in der Gedächtnisdiagnostik und -forschung eine erhöhte Sicherheit bei der Objektivierung möglicher Gedächtnisdefizite bei Personen im Alter von 15-45 Jahren.

Clinical patterns of patients with temporal lobe epilepsy and pure amygdalar atrophy

PURPOSE

MRI volumetric measurements (MRIvol) have been proven reliable in determining mesial temporal atrophy in patients with TLE. We attempted to correlate the clinical features with different patterns of hippocampal formation (HF) and amygdala (AM) atrophy in patients with TLE without foreign tissue lesion.

METHODS

We studied 65 patients with refractory TLE. They were divided into five groups according to MRIvol results: pure AM atrophy (n = 11, 10 unilateral and one bilateral), unilateral HF atrophy (n = 16), bilateral HF atrophy (n = 12), unilateral AM + HF atrophy (n = 13), and patients with normal volumes of AM and HF (n = 13). MRIvol of AM and HF were performed by using a protocol previously described by Watson et al. (Neurology 1992;42:1743-50).

RESULTS

Patients with AM atrophy had later onset of seizures compared with those with unilateral HF atrophy (p < 0.01). History of febrile convulsions (p < 0.0001) and frequent secondarily generalized tonic-clonic seizures (GTCSs) were more often found in patients with HF atrophy compared with those with pure AM atrophy and those with normal volumes (p = 0.04). Prolonged postictal confusion was more often found with AM atrophy (p = 0.05). Memory impairment was more severe in patients with HF atrophy than in those with AM atrophy only or in those with normal volumes (p = 0.03). There were no significant differences among the five groups in the following parameters: age, duration of epilepsy, seizure frequency, and presence and type of aura.

CONCLUSIONS

Prolonged postictal confusion appeared to be related to AM atrophy, in keeping with previous clinical observations. These patients also had a lower incidence of early febrile convulsions, older age at epilepsy onset, lower frequency of secondary GTCS, and lesser memory dysfunction compared with patients with hippocampal atrophy.

Absence of correlation between amobarbital distribution as assessed with SPECT brain perfusion imaging and behavioral manifestations during the intracarotid amobarbital procedure (Wada test)

1. The IAP is used presurgically in patients with temporal lobe epilepsy to predict the effects on LTM and language of the planned temporal lobectomy. This prognosis presumes that a similar pattern of perfusion will result in anesthesia of the same cerebral regions in most patients. 2. Coinjection of Tc-99m HMPAO with the barbiturate during the IAP has been used to ascertain whether this actually is true, with variable results. Moreover, most studies document only unilateral IAPs and do not report on behavioral performance. 3. The authors coinjected Tc-99m HMPAO and amobarbital in 33 IAPs from 18 patients (15 injected bilaterally, 3 unilaterally) to clarify this and to evaluate the relationship of the perfusion pattern to behavioral performance; SPECT results were also compared to angiographic evaluation obtained at the time of catheter placement. 4. SPECT perfusion data was rated for presence/absence and intensity of perfusion to the ACA, MCA, PCA territories and to H, i or c to the injection site. V, STM and LTM were graded according to a standardized protocol. 5. MCAi was perfused in 100% of cases, ACAi in 91%, PCAi in 21% and Hi in only 6%. Cross-over flow was shown in 9 studies; 50% of the patients in whom both sides were injected (on different days) had crossover, involving the ACAc territory in 80% of cases. As expected, injection on the non-ES was associated with a significantly worse LTM performance than on the ES (p = 0.006). There was no relationship between the perfusion pattern and the V level of the patients (a potential confounding variable in memory/language evaluation) during IAP, nor between perfusion pattern and LTM. STM was significantly adversely affected by the presence of crossover perfusion. Angiography in general overestimated the extent of cerebral perfusion demonstrated by SPECT, most probably because of the markedly different injection conditions. 6. Despite the best efforts to standardize injections, the perfusion pattern has been mostly unpredictable in the patients. Moreover, it has little bearing on their behavioral performance, except for the prediction of poor STM performance (the clinical implications of this remaining dubious). Marked LTM alterations after non-ES injections confirm remote hippocampal effects in the presence of only rare direct perfusion of that region. Tc-99m HMPAO/Amobarbital coinjection was unhelpful from a clinical perspective, most probably because a large part of the effects of amobarbital arise from deafferentation of regions not directly perfused by the anesthetic agent.

1H MR spectroscopy in patients with mesial temporal epilepsy

The study provides a review of the basic examination procedures and results of proton magnetic resonance spectroscopy (1H MRS) in patients suffering from mesial temporal lobe epilepsy (MTLE). The source of seizures in MTLE is most often an epileptogenic focus secondary to hippocampal sclerosis. 1H MRS currently plays an important role in the non-invasive diagnosis of this type of epileptogenic lesion. The decisive 1H MRS parameter characterizing an epileptogenic lesion is a statistically significantly decreased value of N-acetylaspartate levels compared with control values, most often associated with a decrease in the ratios of the intensities of NAA/Cr, NAA/Cho and NAA/(Cr + Cho) signals. Moreover, MRS makes it possible to distinguish bilateral involvement of mesial temporal structures typically associated with a bilateral decrease in the levels of metabolites and/or their ratios. As regards other metabolic compounds which play an important role in the pathobiochemistry of epilepsy, MRS is employed to study the action of gamma-aminobutyric acid (GABA), inositol, lactate, glutamine, and glutamate, the clinical function of which has not been fully clarified as yet. It is in this context that one should consider the application of 1H MRS in evaluating the action of some new anti-epileptic agents affecting excitatory and inhibitory amino acids. There is no doubt that in vivo 1H MRS, along with other imaging methods, has made a significant contribution to the clinical and biochemical description of epileptic seizures and has assumed a prominent position among the techniques of pre-operative examination in epileptic surgery.

Observations on the relationship between verbal explicit and implicit memory and density of neurons in the hippocampus

The relationship between neuronal density and verbal memory in left and right hippocampal subfields was investigated in patients who underwent surgery for alleviation of temporal lobe epilepsy. The surgery consisted of unilateral partial removal of the hippocampus along with the anterior temporal lobe and amygdala. Study 1 looked at post-surgical explicit vs implicit verbal memory for lists of words while Study 2 looked at pre- and post-surgical explicit memory for word pairs. Left subfield CA1 appeared to be the most consistently involved in explicit and implicit memory. The results of the two studies confirm presence of hemispheric asymmetry in verbal memory. The notion that hippocampal control of memory is most apparent in post-surgical performance is discussed.

Prediction of verbal memory loss in individuals after anterior temporal lobectomy

PURPOSE

Decreased memory function represents the area of greatest neuropsychological morbidity after anterior temporal lobectomy (ATL), particularly for left ATL candidates. We wished to identify easily derived demographic and neuropsychological predictors of risk of pre- to postoperative memory decline using only information available preoperatively.

METHODS

We assessed decline in memory as measured by the California Verbal Learning Test (CVLT) by deriving multiple regression equations using the following measures as independent variables: age at onset, chronological age at time of surgery, sex, Full Scale IQ (FSIQ), level of education, and preoperative memory scores. In all, 203 patients (93 males, 110 females), undergoing ATL (107 left, 96 right) with preoperative and 6-month postoperative testing, were examined.

RESULTS

The combination of age, FSIQ, sex, side of surgery and preoperative score was highly predictive (p-values < 0.0001) of postoperative memory scores. Higher postoperative scores were associated with higher preoperative score, younger chronological age, higher FSIQ, female sex, and right side of resection. Reliable change index (RCI) values were used to estimate meaningful decline on the total score across five trials. Logistic regression analysis showed preoperative score and age to be predictors of RCI decline for left-sided resections. Sensitivity of decline (> or =90th centile RCI) prediction was 56%, and specificity was 95%. Validation in 30 patients from a separate population of patients undergoing left ATL produced similar figures.

CONCLUSIONS

The derived regression equations can accurately predict verbal memory decline on a list-learning task in approximately 50% of individual patients undergoing ATL, and false-positive prediction errors are very rare.

Naming decline after left anterior temporal lobectomy correlates with pathological status of resected hippocampus

PURPOSE

To evaluate the determinants of postoperative change in visual confrontation naming ability and the differential sensitivity of two common tests of confrontation naming.

METHODS

In a group of 99 patients undergoing lobectomy of the left, language-dominant anterior temporal lobe, we examined naming ability using two measures: the 60 item Boston Naming Test (BNT), and the Visual Naming (VN) subtest of the Multilingual Aphasia Examination (MAE). ATL entailed resection of lateral temporal lobe followed by microsurgical complete removal of hippocampus. Language mapping was not performed. The status of the resected hippocampus was graded on a scale 0-4 of hippocampal sclerosis (HS). A dichotomous grouping HS- (grades 0 and 1, n = 34) and HS+ (grades 3 and 4, n = 61) was effected. Age at surgery, age of epilepsy onset, sex, extent of lateral temporal resection, Full-Scale IQ (FSIQ), and preoperative naming scores were also examined as potential predictors of pre- versus postoperative naming change.

RESULTS

Preoperative BNT and VN scores were significantly worse for HS+ than for HS- (BNT, p < 0.05; VN, p = 0.001). Postoperatively, BNT and VN scores significantly declined for HS- as compared with HS+ patients (p < 0.001). For individual risk, the 90th centile of reliable change index (RCI) was used. By this criterion, of the total sample, 39% evidenced decline on the BNT and 17% evidenced decline on the VN. Logistic regression analysis with backward elimination showed HS to be the only predictor of decline in BNT and HS and sex to be the only predictors of VN decline. Males were more at risk than females. Age, age at onset, extent of lateral resection, preoperative scores, and FSIQ were not predictors. Using age at onset as a proxy for HS+/HS- we calculated probabilities for naming decline for given onset age.

CONCLUSIONS

Both preoperative and postoperative change in naming ability are associated with the pathological status of the hippocampus. The potential interpretations and implications of these findings are discussed.

Functional plasticity after left anterior temporal lobectomy: reconstitution and compensation of verbal memory functions

PURPOSE

This study investigated the functional plasticity of the brain to reconstitute and compensate for verbal memory functions after epilepsy surgery of left temporocortical and temporomesial structures. We hypothesized that memory outcome would be best when surgery is performed within the period of cerebral plasticity, and that the outcome should be worst when fluid intelligence starts to decrease with physiologic aging. We also raised the question of different plasticity and compensation mechanisms for temporomesial and temporocortical memory functions.

METHODS

We evaluated preoperative and 1-year-postoperative memory data and other verbal functions in 104 patients with epilepsy, who underwent a standard left anterior temporal lobe resection. We used memory measures that had been previously shown to be most selective for mesial and lateral functions, respectively. Determinants of postoperative memory outcome were evaluated by multiple regression analysis. Group statistics were calculated on the basis of the periods that are usually assumed to be significant for plasticity and behavioral compensation. Individual postoperative changes in memory functions were evaluated on the basis of test-retest data obtained in a group of 100 nonsurgical patients with localization-related epilepsies (mean retest interval >12 months).

RESULTS

Only changes in cortically represented learning and data acquisition were related to age, plasticity, and capacities for behavioral compensation. No patient in the youngest group (younger than 15 years), 33% of patients who had surgery between the ages of 15 and 30 years, and 61% of the patients undergoing surgery older than age 30 years had significant deterioration in verbal learning. In contrast, postoperative changes in temporomesial consolidation/retrieval processes were independent of age at the time of surgery, plasticity, and capacities for behavioral compensation.

CONCLUSIONS

Our data indicate different time windows for the reconstitution and compensation of mesial and cortical aspects of memory. Whereas the reconstitution of and compensation for cortical functions appear restricted by decreasing plasticity and physiological aging, mesial functions seem to be reconstituted by contralateral mesial structures over a much longer period. Concerning drug-resistant localization-related epilepsies, our results justify early consideration of surgery, especially when cortical structures are affected.

Neuroimaging in epilepsy

Neuroimaging techniques have improved the understanding, diagnosis, and management of epilepsy. By providing excellent structural information, MRI is the technique of choice in evaluating patients with epilepsy. Functional imaging techniques, including MR spectroscopy, functional MRI, positron emission tomography, and single photon emission CT, permit noninvasive assessment of the epileptic substrate, its functional status, and neuroreceptors. The MRI-based techniques will potentially assume a greater role in the cost-effective workup of the patient. Currently, newer techniques such as magnetoencephalography, magnetic source imaging, and optical imaging are research tools.

Anterior temporal lobectomy, hippocampal sclerosis, and memory: recent neuropsychological findings

Anterior temporal lobectomy (ATL) is an effective and increasingly utilized treatment for nonlesional, intractable mesial temporal lobe epilepsy. However, this surgery results in domain-specific neuropsychological morbidity for a subset of patients. Within the past decade, multidisciplinary studies have revealed that left ATL patients without significant sclerosis in the resected hippocampus are most at risk for a substantial postacute decline in the ability to encode new verbal information. These patients are also at risk for a significant decrement in confrontation naming and other retrieval-based language abilities. The memory deficit is not attributable to this disruption of language. A relationship between hippocampal sclerosis (HS) status and memory performance has not been identified consistently in right ATL patients, but investigation of new visuospatial measures continues. The influence of variables other than HS on neuropsychological outcome is also discussed.

The relationship between quantitative MRI and neuropsychological functioning in temporal lobe epilepsy

PURPOSE

Quantitative MRI techniques provide an unparalleled opportunity to examine in vivo the relationship between the extent and laterality of hippocampal pathology and associated neuropsychological deficits. The purpose of this study was to examine the nature of the relationship between quantitative measures of hippocampal pathology and neuropsychological measures, using a multivariate approach.

METHODS

We examined the relationship between two MRI measures of hippocampal structure; hippocampal volumes (HCvol) and T2 relaxation times (HCT2), and memory performance, in 80 presurgical temporal lobe epilepsy patients.

RESULTS

As a group, patients with left hippocampal sclerosis (LHS) performed more poorly that those with right hippocampal sclerosis (RHS) on immediate and delayed prose recall. In the group as a whole, right hippocampal volume was significantly correlated with the delayed recall of a complex figure. None of the verbal memory test scores were significantly correlated with the right or left HCvol or HCT2 measures. However, stepwise multiple regression analyses indicated that up to a third of the variation in specific test scores could be explained by the quantitative MRI hippocampal measures in conjunction with chronological age, and age at onset of habitual epilepsy. Left hippocampal measures explained 24% of the variance in the story-recall tasks, while right hippocampal measures explained 18% of the variance in a design-learning task and 32% of the variance in a figure-recall task.

CONCLUSIONS

Our results provide some support for the lateralised model of material specific memory deficits, but suggest that a number of demographic and epilepsy-related factors may interact with the extent and laterality of hippocampal pathology in shaping the nature of the associated neuropsychological deficit.

Memory, simple and complex language, and the temporal lobe

Nineteen patients with intractable temporal lobe epilepsy who underwent anterior temporal lobectomy were given a highly specific memory battery (23 tests) pre- and post- (1 week; 1, 2, and 6 months; 1 and 2 years) resection. Sixteen of 23 tests revealed that memory performance of temporal lobe epilepsy patients was worse than normal controls prior to surgery (p < .001), while the most profound differences were seen in the remembering and generation of inferences from connected discourse. Almost no differences were observed in delayed nonmatching to sample tasks (recognition without language task). MRI results revealed that anterior, middle, and posterior hippocampal abnormality was extensive in 12 of 19 patients, and 12 also showed medial temporal lobe abnormalities and volume loss. Hippocampal damage was negatively correlated with extended delay memory performance for connected discourse: worse performance was associated with greater damage. Few differences in less complex memory performance were observed pre-postsurgery. While ordinary recognition functions were preserved, results demonstrated that dominant medial temporal lobe structures appeared heavily involved in language-generated memory, and hippocampus is heavily implicated in both simple and complex language.

Recent advances in epilepsy surgery: temporal lobectomy and multiple subpial transections

THIS ARTICLE REVIEWS four major advances in epilepsy surgery, especially the most frequently performed surgery, temporal lobectomy, as follows: 1) the ability to preoperatively identify (using magnetic resonance imaging) the pathological condition of hippocampal sclerosis (a key component to the syndrome of mesial temporal lobe epilepsy, 2) the ability to identify preoperatively which temporal lobe candidates are at risk for postoperative memory problems, 3) the standardization of temporal lobectomy with respect to how much hippocampus should be resected, 4) a validation of the novel surgical technique of multiple subpial transections. This technique allows surgeons to attack foci within nondispensible cortex and therefore enlarges the applicability of surgical treatment to otherwise inoperable patients and potentially improves outcome.

Quantitative MRI in outpatient childhood epilepsy

PURPOSE

In adult studies, MRI volumetrics is a proven technique in presurgical assessment of epilepsy. Hippocampal volume loss is maximal in the syndrome of mesial temporal lobe epilepsy. We aimed (a) to validate this methodology in a pediatric outpatient epilepsy population (b) to determine the relationship of hippocampal asymmetry (HA) to epileptic syndromes and risk factors.

METHODS

Two neurologists classified the epileptic syndrome in 79 pediatric outpatients, according to the International Classification of Epilepsies and Epileptic Syndromes (ILAE). Hippocampal volumetrics were performed in all patients. HA was defined according to adult control values.

RESULTS

Inter-rater variability on measurement of HA was very small (Correlation of test retest of 0.97 on 17 children <3 years old). The rate of HA was 44/79 (57%). In 21 patients, (27%) potentially epileptogenic lesions (other than HA) were identified (cerebral dysgenesis n = 11). HA was present in 9/15 (60%) of temporal lobe epilepsy and in 15/28 (54%) extratemporal onset epilepsy and 5/11 (46%) of generalized symptomatic epilepsy. Analysis confined to <13 years also showed HA was not specific for epileptic syndrome. There was no significant association of febrile convulsions (13%) with HA or temporal lobe epilepsy.

CONCLUSIONS

There is a high incidence of HA in childhood epilepsy. HA was not confined to clinically defined temporal lobe epilepsy. The poor correlation of epileptic syndrome to quantitative MRI findings may be due to the inadequacies of epilepsy classification in the younger child, with the clinical semiology providing misleading localizing information. Normative childhood data for hippocampal volumes and symmetry is needed.

Bilateral reductions in hippocampal volume in adults with epilepsy and a history of febrile seizures

OBJECTIVES

To examine the degree and frequency of reductions in hippocampal volume in patients with temporal lobe epilepsy with and without a history of febrile seizures.

METHODS

In vivo measures of hippocampal volume were computed from three dimensional gradient echo (FLASH) images in 44 patients undergoing comprehensive evaluations for epilepsy surgery. Twenty one patients (48%) reported a history of febrile seizures. The volumes from these patients were compared with those from 23 patients without a history of febrile seizures and 34 healthy controls.

RESULTS

The febrile seizure group had significant reductions in volume, both ipsilateral (30% decrease) and contralateral (15% decrease), to the EEG seizure focus. Twelve of 18 patients with febrile seizures exhibited clinically significant ipsilateral volume reductions, defined as volumes falling 2 SD below the mean obtained from the control sample. Only four of 19 patients without febrile seizures exhibited this degree of reduction. No significant correlations were found between seizure variables (for example, duration of epilepsy, seizure frequency) and ipsilateral reductions in volume. However, a significant inverse correlation (r=-0.45, P<0.05) between seizure frequency and the volume of the hippocampus contralateral to the seizure focus was found in the febrile seizure group.

CONCLUSION

These results suggest that a history of febrile seizures is associated with the finding of a smaller hippocampus on the side ipsilateral to the subsequent temporal lobe focus whereas chronic factors seem to be be related to pathology contralateral to the seizure focus.

Reorganization of verbal memory function in early onset left temporal lobe epilepsy

The purpose of this investigation was to examine the issue of reorganization of verbal memory function following early insult to the left mesial temporal region. It was hypothesized that reorganization of memory function was most likely to occur in those patients with an early age of seizure onset who have a more limited degree of extra-hippocampal neuropathology. Fifty-four patients with epilepsy of unequivocal left temporal lobe origin were classified into four groups on the basis of the presence/absence of hippocampal sclerosis and degree of postoperative seizure relief. Measures of verbal learning and memory as well as nonmemory measures were administered both before and 6 to 8 months after anterior temporal lobectomy. Findings were consistent with the reorganization proposal. The clinical and theoretical significance of the findings are discussed.

Differential involvement of left temporolateral and temporomesial structures in verbal declarative learning and memory: evidence from temporal lobe epilepsy

A wealth of animal and human research has pointed to a significant involvement of the temporal lobes in memory processing, and yet the different functional roles of temporal cortical vs. mesial structures remain unclear. We studied verbal declarative memory, by using a word list paradigm that differentiates among learning (immediate recall), memory (delayed recall), and recognition, in epilepsy patients being considered for surgical resection of the left temporal lobe. Verbal memory was evaluated preoperatively and during the recording of intracranial event related potentials and postoperatively after selective hippocampectomy, temporal cortical lesionectomy, or anterior two-thirds en bloc temporal lobe resection procedures. Preoperative differences in verbal memory performance as a function of differences in underlying neuropathology, concurrent event-related potentials, and specific patterns of postoperative memory impairments lead to converging evidence that verbal declarative memory relies on a synergistic interaction of at least two functionally distinct brain systems. Material-specific data acquisition, or working memory, is mediated by neocortical temporal structures, whereas long-term consolidation/retrieval is particularly mediated by temporomesial structures. In contrast to the left temporal neocortex, the function of the temporomesial system appears to be material nonspecific. Apparently, its preferential involvement in verbal memory is due to its close interaction with overlying neocortical structures that are specialized for language processing.

The relation between quantitative MRI measures of hippocampal structure and the intracarotid amobarbital test

PURPOSE

The increasing sophistication of quantitative magnetic resonance imaging (MRI) techniques has generated hopes that they may eventually supersede the intracarotid amobarbital procedure (IAP) in the presurgical screening for bilateral abnormalities in prospective candidates for temporal lobe epilepsy surgery. As the first step toward this aim, the purpose of this study was to examine the relationship between these measures of structural and functional integrity.

METHODS

We examined the relation between memory performance and pass/fail rates on the IAP and two MRI measures of hippocampal integrity: hippocampal volumes, adjusted for intracranial volume (HCvol) and hippocampal T2 relaxometry (HCT2), in 48 patients with medically intractable temporal lobe epilepsy, who underwent the IAP as part of their presurgical evaluation for temporal lobectomy.

RESULTS

The unilateral memory scores from the IAP were not significantly correlated with the corresponding HCvol or HCT2 measures in the right- and left-temporal-lobe groups. However, the MRI measures of hippocampal asymmetry (right minus left HCvol, right minus left HCT2) were significantly correlated with our measure of functional asymmetry, the right minus left hemisphere memory score from the IAP, supporting the role of the IAP in lateralising temporal lobe dysfunction. Forty-six patients with unilateral hippocampal sclerosis and concordant EEG studies passed the IAP. Two patients failed the memory component of the IAP. In both cases, other presurgical investigations suggested bilateral abnormalities.

CONCLUSIONS

We conclude that patients with unilateral hippocampal sclerosis, established by a rigorous quantitative MRI protocol, and concordant ictal and interictal EEG findings may not be at risk for postoperative amnesia, despite baseline neuropsychological deficits suggestive of bilateral disturbance.

Reliability and validity of MRI measurement of the amygdala and hippocampus in children with fragile X syndrome

Evidence from numerous structural magnetic resonance imaging (MRI) studies has converged to implicate mesial temporal lobe structures in the pathophysiology of several developmental and psychiatric disorders. Efforts to integrate the results of these studies are challenged, however, by the lack of consistency, detail and precision in published protocols for the manual measurement of the amygdala and hippocampus. In this study, we describe a highly detailed, standardized protocol for measuring the amygdala and the hippocampus. Within the context of this protocol, we tested the inter- and intra-rater reliability of two frequently cited methods for normalizing the anatomical position of the amygdala and hippocampus prior to measurement. One method consisted of creating a coronal data set in which images are rotated in a plane perpendicular to the long axis of the hippocampus. The second method consisted of creating a coronal data set in which images are rotated in a plane perpendicular to the axis connecting the anterior and posterior commissures. Inter- and intra-rater reliability coefficients (using the intraclass correlation) ranged from 0.80 to 0.98, indicating that both methods for positional normalization are highly reliable. In addition, we tested the validity of each method by comparing the temporal lobe anatomy of children with fragile X syndrome to a group of unaffected children matched by age and gender. We found that hippocampal volumes in children with fragile X were significantly increased when either rotational method was used. These results replicated previous findings, suggesting that either method can be validly applied to neuronanatomic studies of pediatric populations.

Use of the intracarotid amobarbital procedure in the evaluation of memory

The intracarotid amobarbital procedure (IAP) involves the temporary inactivation of one cerebral hemisphere by the injection of sodium amobarbital, which allows independent testing of the contralateral hemisphere. Initially used for lateralization of language, IAP later found a role in the evaluation of memory function in patients with intractable temporal lobe epilepsy being considered for resective surgery. IAP technique varies widely across centers, but, in general, memory is assessed by presenting the patient with a number of items during the period of hemispheric inactivation and testing recall or recognition of these items after the effect of the drug has worn off. Because the medial temporal lobe is not directly perfused by the internal carotid artery, concerns have been raised about the ability of the IAP to test hippocampal memory function. Consequently, a variety of selective procedures have been devised. Findings on both intracranial EEG recordings and pathologic and neuroimaging studies support the association of IAP memory results with hippocampal function. The IAP memory test was originally designed to predict the risk for development of global amnesia following unilateral temporal lobectomy. More recently, it also has been used as an adjunct in lateralizing the seizure focus and for predicting postoperative selective memory deficits and seizure outcome.

Structural brain changes in PTSD. Does trauma alter neuroanatomy?

Although the impetus for studying hippocampal morphology and functioning in PTSD was the finding that stress could result in hippocampal damage in rodent and primate models, it is far from proven that the findings to date in PTSD represent defects that have been caused by trauma. It is equally possible that the findings represent a preexisting anomaly which might serve as a risk factor for the development of PTSD following trauma exposure. To resolve this dilemma, it is necessary to study persons at high risk for trauma (e.g., soldiers) prior to trauma exposure and ag in after exposure. Such methods will permit the determination not only of whether trauma alters hippocampal morphology, but also, if so, of whether this effect is limited to persons with PTSD. At the present time, the field would be well advised to proceed vigorously but with appropriate caution along these lines of research. As just outlined, sample sizes have been small, and potentially confounding variables have abounded in most studies. The next few years of research may well continue to replicate the finding of abnormal hippocampal morphology in PTSD. However, it would not be surprising to find that other brain regions are also involved and that these represent part of a broader risk spectrum for the development of psychopathology under stress. Until these issues are clarified, the neuroanatomical findings to date in PTSD should be viewed as tentative, tantalizing, and in need of additional study.

Degree of left hippocampal atrophy correlates with severity of neuropsychological deficits

The relationship between the degree and distribution of hippocampal atrophy measured by volumetric magnetic resonance imaging and severity of memory deficits in 25 patients with temporal lobe epilepsy secondary to mesial temporal sclerosis was assessed. Hippocampal volumes were expressed as a ratio of smaller to larger, normal ratio greater than 0.95. Neuropsychology tests included: subtests of the WAIS-R, Rey Auditory Verbal Learning Task, Rey Figure and the Austin Maze. Degree of left hippocampal atrophy in patients with left temporal lobe epilepsy was associated with severity of verbal memory deficits as measured by RAVLT total recall (P < 0.05), delayed recall (P < 0.001), story recognition (P < 0.001), list recognition (P < 0.001) and final delayed recall (P < 0.001) and recall of the Rey Figure (P < 0.01). There was no association between degree of right hippocampal atrophy and any of the memory tests. Diffuse left hippocampal atrophy was associated with more severe verbal memory deficits than anterior atrophy. We conclude, the association between degree of left hippocampal atrophy and verbal memory provides further evidence of the predominant involvement of the left hippocampus in verbal memory. The finding of a relationship between degree of left hippocampal atrophy and measures of non-verbal function suggests these tests are dependent on verbal memory, or that mesial temporal sclerosis is a bilateral but asymmetrical condition.

Hippocampal volumetry with magnetic resonance imaging: a cost-effective validated solution

PURPOSE

The clinical utility of hippocampal volumetry is well documented, but the materials and techniques required to perform the procedure are not widely available outside major research centers. We describe a personal computer-based method of volumetric data analysis.

METHODS

Using a 1.0-T scanner, we obtained 2-mm-thick tilted coronal MPRAGE magnetic resonance imaging (MRI) scans of 20 healthy volunteers aged 20-38 years. We used an inexpensive utility program to extract image information and an NIH Image for image analysis. The hippocampal formations were traced with a graphics tablet and landmarks described by Watson et al. (Neurology 1992;42:1743-50). Overlays of individual observers' tracings were used to fine tune the selection of landmarks and boundaries. Filled-in silhouette pairs generated from these "training tracings" were compared to determine how well observers could visually quantify area differences.

RESULTS

Visual detection of asymmetry of silhouette pairs was sensitive, but the magnitude of asymmetry was underestimated. We achieved intraobserver coefficients of variation of right/left volume ratios between 0.82 and 3.16 and an interobserver range of volume ratios of 6%. In 20 healthy controls aged 20-38 years, the mean right and left hippocampal volumes were 2,911 mm3 and 2,836 mm3, respectively. The lower limits of normal were 2,217 mm3 for the right and 2,178 mm3 for the left. The mean right/left hippocampal ratio was 1.03, and the limits of normal (3 SD) for this were 0.95 to 1.10.

CONCLUSIONS

Hippocampal volumetry can be performed reliably and economically. Our methodology makes it possible for different observers to generate consistent and comparable measurements.

Neuropsychological evaluation in epilepsy surgery

Neuropsychology has played a prominent role throughout the modern era of epilepsy surgery. Neuropsychology, including the Wada test, has been of benefit in documenting dysfunction associated with a lateralized temporal lobe seizure onset. In addition, neuropsychological results have some predicative power regarding seizure outcome following anterior temporal lobectomy. The current status of neuropsychology in patient evaluation and outcome prediction will be presented. Differences between the Wada test, an inactivation procedure, and functional magnetic resonance imaging, which is an activation procedure, will be discussed. This paper will also present preliminary information about the Wechsler Adult Intelligence Scale-III, the recent revision of the most commonly used test of intellectual function, and its effects on neuropsychological performance results.

The spectrum of hippocampal sclerosis: a quantitative magnetic resonance imaging study

One hundred patients with intractable temporal lobe epilepsy and 22 control subjects were scanned on a 1.5-T Siemens SP63 Magnetom scanner. A combination of hippocampal T2 mapping, hippocampal volume measurement corrected for intracranial volume, and inspection of hippocampal morphology on a hippocampal volume distribution graph compared with a control graph revealed previously undetected forms of bilateral hippocampal sclerosis and four false-positive diagnoses of hippocampal sclerosis made on visual inspection of the scans. A physiological asymmetry in the position of the hippocampi in 41% of control subjects and focal hippocampal atrophies in patients made measurement of the whole length of the hippocampus mandatory. The extent of hippocampal damage in patients with hippocampal sclerosis correlated with the number of secondary generalized seizures during a patient's lifetime. In contrast to patients with unilateral hippocampal sclerosis, patients with severe bilateral hippocampal sclerosis had no history of febrile convulsions. Twenty-six patients with intractable temporal lobe epilepsy had normal hippocampal magnetic resonance imaging measures and as a group were significantly older at the onset of habitual epilepsy than were patients with hippocampal sclerosis. In conclusion, a combination of quantitative magnetic resonance imaging techniques revealed a spectrum of hippocampal sclerosis and optimally defined boundaries of hippocampal normality. The spectrum of hippocampal sclerosis is related to the etiology, the number of secondary generalized seizures, and the age at onset of habitual epilepsy.

Neuropsychologic assessment in surgical treatment of epilepsy

Neuropsychologic assessment has long been an integral part of evaluation for surgical treatment of epilepsy. Neuropsychologic evaluation and consultation continue to be an important part of the assessment for operative intervention for epilepsy, but the role of neuropsychology has changed over time. At one time, neuropsychologic assessment assumed a diagnostic role in preoperative evaluation for epilepsy and also contributed to the lateralization and localization of the seizure focus. Sophisticated electroencephalographic techniques and especially neuroimaging have revolutionized the diagnosis and management in epilepsy surgical treatment centers. Although still helpful, neuropsychology no longer has a major role in lateralization or localization of seizure onset. This report describes neuropsychologic evaluation and its current role in surgical treatment of epilepsy. The characteristics and purposes of neuropsychologic assessment and Wada testing (intracarotid injection of amobarbital) are described. Current research on assessment of emotional adjustment and on its predictors before and after surgical therapy for epilepsy is reviewed. Finally, the risk for neuropsychologic decline after temporal lobectomy is discussed in light of recent research on preoperative memory, hippocampal pathologic lesions, and quantitative neuroimaging data.

Visuomotor learning in cerebellar patients

The aim of the present study was to demonstrate that patients with pathology affecting substantial regions of the cerebellum can improve their performance in a series of two-dimensional tracing tasks, thus supporting the view that this type of motor behavior can be acquired even when the integrity of this structure is compromised. Eight patients with chronic, isolated cerebellar lesions and eight age- and sex-matched healthy controls were tested. Three patients had mild, five had moderate upper limb ataxia. The experiment was divided into two parts. In the first, subjects traced an irregularly shaped outline over 20 consecutive trials ('Trace 1' task). Next, subjects were asked to redraw the object without any underlying template as a guide ('Memory 1' task). In the second part of the study, subjects were asked to trace a different, irregularly shaped outline over 20 consecutive trials ('Trace 2' task). Next, they were required to redraw it by memory with its axis rotated 90 degrees ('Memory 2' task). In each of the memory tasks the template was placed over the drawn image after each trial and shown to the subjects. The error of performance was determined by calculating three different measurements, each focused on different aspects of the task. Based on these measurements, the cerebellar patients showed improvement in both memory tasks. In the 'Memory 1' task the calculated error decreased significantly for the patients with mild ataxia. In the 'Memory 2' task all cerebellar patients improved their performance substantially enough to reduce significantly the magnitude of all three error measurements. The experiments demonstrate that patients with cerebellar lesions are capable of improving substantially their performance of a complex motor task involving the recall of memorized shapes and the visuomotor control of a tracing movement.

Effects of temporal lobe epilepsy on spatial and figural aspects of memory for a complex geometric figure

The preoperative delayed memory performance on the Rey-Osterrieth Complex Figure (Lezak, 1983) of 54 patients with complex partial seizures of temporal lobe origin was analyzed using 3 different indices. One index (composite) was derived using a common scoring method that included both spatial and figural aspects of memory in its score. The other two indices were derived emphasizing either spatial or figural aspects of memory for the elements of the figure separately. All 3 indices distinguished between individuals with right-sided (RTLE) and left-sided (LTLE) seizure onset. However, spatial memory was significantly lower than figural memory in individuals with RTLE as compared to those with LTLE. Both the spatial and figural memory indices were significantly lower in the presence of magnetic resonance imaging (MRI) evidence for hippocampal sclerosis in individuals with RTLE. Results suggest that while both the spatial and figural aspects of nonverbal memory are sensitive to right hippocampal dysfunction, figural memory may be less vulnerable to the effects of RTLE.

Medial temporal lobe heterotopia as a cause of increased hippocampal and amygdaloid MRI volumes

Magnetic resonance imaging (MRI)-based volumetric measurements of the hippocampus and amygdala are useful in detecting hippocampal and amygdaloid sclerosis in patients with temporal lobe epilepsy. In these pathological entities, volumetric MRI analysis shows the epileptogenic structures to be atrophic when compared to the normal, nonepileptogenic side. Described are 2 patients with increased hippocampal and amygdaloid volumes on the side of seizure onset due to medial temporal lobe heteroto pias. Care must be taken in the interpretation of volumetric MRI data to make certain that asymmetries in hippocampal and amygdaloid measurements are due to atrophy and sclerosis of the abnormal side and not to increased tissue such as heterotopic gray matter.

Empirical techniques for determining the reliability, magnitude, and pattern of neuropsychological change after epilepsy surgery

PURPOSE

We assessed test-retest neuropsychological performance in patients with complex partial seizures to derive reliable change indices (RCIs) and regression-based norms for change, indices that may be helpful in assessing cognitive outcome after anterior temporal lobectomy.

METHODS

Forty patients with complex partial seizures (CPS) who did not undergo epilepsy surgery were administered a comprehensive neuropsychological battery on two occasions. Their test-retest data were used to compute both RCIs and regression-based norms for change for each neuropsychological index. RCIs corrected for practice effects provide a confidence interval (CI) indicating the degree of performance change required to exceed the variability attributable to sources of error (e.g., practice, test-retest reliability). Regression-based norms for change also correct for several sources of measurement error and examine observed versus expected test-retest changes on a common metric, thereby facilitating determination of the degree and relative magnitude of change across cognitive domains.

RESULTS

Mean changes in test-retest performance were generally modest, but were evident across several test measures. Our data indicate a considerable degree of individual variability in test-retest performance.

CONCLUSIONS

RCIs and regression-based norms are complementary indexes and can be particularly useful in examining the test-retest performance of individual patients who undergo epilepsy surgery as well as in the more general investigation of cognitive outcome after epilepsy surgery.

Mesial atrophy and outcome after amygdalohippocampectomy or temporal lobe removal

We studied 74 consecutive patients with temporal lobe epilepsy who were treated surgically and in whom the volumes of mesial temporal structures were determined preoperatively by magnetic resonance imaging. We divided the patients into three groups according to the volumetric findings: unilateral (63.5% of the patients), bilateral (23%), or no atrophy (13.5%) of the amygdala-hippocampal formation. Two distinct surgical approaches were used: selective amygdalohippocampectomy (n = 37) or anterior temporal lobe resection (n = 37). Outcome was assessed at least 1 year after surgery, according to Engel's modified classification. Patients with unilateral mesial temporal atrophy had significantly better results compared with the other two groups (p < 0.001): We found excellent results (class I or II outcome) in 93.6% of the patients with unilateral atrophy, in 61.7% of those with bilateral atrophy, and in 50% of the group with no significant atrophy of mesial temporal structures. The two different surgical techniques were equally effective, regardless of the pattern of atrophy. In conclusion, magnetic resonance volumetric studies in temporal lobe epilepsy proved to be an important preoperative prognostic tool for surgical treatment, but they did not provide guidance for selecting one surgical approach compared to the other.

Hippocampal sclerosis and verbal encoding ability following anterior temporal lobectomy

Previous research has shown that the degree of verbal memory decline following left anterior temporal lobectomy (ATL) is inversely related to the extent of neuronal dropout in resected left hippocampus. The goal of this investigation was to clarify further the nature of the free recall impairment and to determine the relative contribution of verbal retrieval and encoding processes. Seventy-six patients who underwent left (n = 46) or right (n = 30) ATL were classified according to the presence or absence of hippocampal sclerosis and pre- to postoperative changes in free recall, cued recall and recognition memory for verbal material were examined. Surgically induced free recall impairments were selectively associated with resection of nonsclerotic left hippocampus and represented a 29-35% decline in verbal learning ability. These free recall deficits were due to postoperative impairment in verbal encoding efficiency, not retrieval difficulties. Assessment of false positive recognition errors indicated that resection of nonsclerotic left hippocampus selectively impaired the ability to encode stimulus uniqueness within correct semantic fields. The clinical and theoretical significance of these results are discussed.

The effects of human hippocampal resection on the serial position curve

The purpose of this study was to examine the contribution of the human hippocampal formation to the classic serial position curve. Seventy-seven patients who underwent anterior temporal lobectomy (ATL) (47 left, 30 right) were administered a list learning task before and after surgery, and changes in the serial position curve were examined. Forty nonsurgical patients with complex partial seizures were tested at comparable intervals and served as controls. Changes in the serial position curve were seen only after left ATL, and almost exclusively among patients without hippocampal sclerosis. Patients without left hippocampal sclerosis, and who therefore underwent resection of hippocampus that was to a considerable degree structurally (and presumably functionally) intact, showed significant declines in recall from the primacy and middle portions of the list compared to all other groups. There was no change in the recency portion of the list. Patients with left hippocampal sclerosis showed only a modest decline in recall from the middle region compared only to the control group, and the right ATL groups did not show any significant changes in serial position recall. These findings demonstrate the contribution of the left hippocampus to those discrete portions of the serial position curve which rely on secondary memory, and have implications for assessing the effects of ATL on memory function.

Bilateral magnetic resonance imaging-determined hippocampal atrophy and verbal memory before and after temporal lobectomy

We investigated pre- and postoperative verbal memory in temporal lobectomy patients who had volumetrically symmetric hippocampi. Pre- and postoperative verbal memory data based on the Logical Memory subtest of the Wechsler Memory Scale-Revised (WMS-R) were obtained from 15 left and 18 right temporal lobectomy patients. The difference between hippocampal volumes (R/L) was between -0.1 and 0.3 cm3, which is indeterminate for lateralizing hippocampal atrophy. Patients were divided into four groups based on side of operation and combined hippocampal volume expressed as a function of total intracranial volume (R + L volume/total intracranial volume). Patients with a combined hippocampal volume that was smaller than any combined hippocampal value of a normal control group were defined as bilaterally atrophic. Left temporal lobectomy patients demonstrated the expected decrease in verbal memory postoperatively regardless of whether the volumetrically symmetric hippocampi were nonatrophic or atrophic. Left temporal lobectomy patients with bilaterally atrophic hippocampi, however, had the poorest verbal memory before and after operation. Right temporal lobectomy patients tended to have improved verbal memory after operation whether or not the volumetrically symmetric hippocampi were atrophic. We conclude that side of operation is a more potent predictor of verbal memory outcome than is hippocampal atrophy when hippocampi are bilaterally symmetric and that left temporal lobectomy patients with bilateral atrophy may be at risk for greater functional deficits after operation.

Quantified volumes of temporal lobe structures in patients with epilepsy

The T1-weighted volumetric magnetic resonance images of 31 patients with intractable temporal lobe epilepsy, and 13 control subjects matched for age and sex, were subjected to semiautomated threshold analysis. The method used proved to be relatively fast and reliable. An index of temporal lobe interhemispheric asymmetry was extracted by thresholding high-signal (white matter) pixels. Patients had significantly more asymmetrical indices for white matter and hippocampal volumes that did control subjects, and the two indices were significantly correlated, providing evidence for the validity of the white matter index. Differences in both indices were consistent with decreased tissue on the side of the focus. In classification analyses a combination of these two indices correctly predicted the side of focus at a greater rate than did either used alone. Findings provide support for the hypothesis that seizure activity is associated with atrophy in both mesial and lateral temporal lobe structures.