Correlation of temporal lobe glucose metabolism with the Wada memory test

PURPOSE: The goal of the present study was to examine the relationship of 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) and the Wada memory test in lateralizing memory dominance and epileptic focus. METHODS: FDG-PET and the Wada test were performed in 18 patients with temporal lobe epilepsy (TLE). The asymmetry indices of FDG-PET (PET-AI) were calculated in mesial, polar, anterolateral, midlateral, and posterolateral regions of the temporal lobe, and those of Wada memory test (Wada-AI) were obtained as well. RESULTS: The Wada-AI was significantly correlated with PET-AI in mesial (r = 0.67, p = 0.003), polar (r = 0.55, p = 0.019), anterolateral (r = 0.55, p = 0.019), and midlateral (r = 0.51, p = 0.031) regions of the temporal lobe. However, after a linear regression analysis, PET-AI of only the mesial temporal region was significantly correlated with Wada-AI (p = 0.008). Wada-AI could correctly lateralize the seizure focus in 90% of the left TLE and 75% of the right TLE patients. The PET-AI of the mesial temporal region showed the highest sensitivity of seizure lateralization (80% of left TLE and 87.5% of right TLE). PET-AI of other temporal regions had lower sensitivities (50-80% of left TLE, 20-75% of right TLE). One or two patients showed false seizure lateralization by PET-AI on each temporal region. CONCLUSIONS: Although FDG-PET hypometabolism is observed at both mesial and lateral regions of the temporal lobe in mesial TLE, mesial temporal region appeared to be a dominant and leading area for lateralizing Wada memory dominance and epileptic focus.     

Prediction of seizure-onset laterality by using Wada memory asymmetries in pediatric epilepsy surgery candidates

PURPOSE: Because the capacity of intracarotid amobarbital (Wada) memory assessment to predict seizure-onset laterality in children has not been thoroughly investigated, three comprehensive epilepsy surgery centers pooled their data and examined Wada memory asymmetries to predict side of seizure onset in children being considered for epilepsy surgery. METHODS: One hundred fifty-two children with intractable epilepsy underwent Wada testing. Although the type and number of memory stimuli and methods varied at each institution, all children were presented with six to 10 items soon after amobarbital injection. After return to neurologic baseline, recognition memory for the stimuli was assessed. Seizure onset was determined by simultaneous video-EEG recordings of multiple seizures. RESULTS: In children with unilateral temporal lobe seizures (n = 87), Wada memory asymmetries accurately predicted seizure laterality to a statistically significant degree. Wada memory asymmetries also correctly predicted side of seizure onset in children with extra-temporal lobe seizures (n = 65). Although individual patient prediction accuracy was statistically significant in temporal lobe cases, onset laterality was incorrectly predicted in < or =52% of children with left temporal lobe seizure onset, depending on the methods and asymmetry criterion used. There also were significant differences between Wada prediction accuracy across the three epilepsy centers. CONCLUSIONS: Results suggest that Wada memory assessment is useful in predicting side of seizure onset in many children. However, Wada memory asymmetries should be interpreted more cautiously in children than in adults.     

Wada memory performance predicts seizure outcome after epilepsy surgery in children

PURPOSE: Wada memory asymmetries were examined in children from four comprehensive epilepsy surgery centers who subsequently underwent epilepsy surgery to determine whether Wada memory performance could predict degree of seizure relief in children. METHODS: One hundred fifty-six children (between ages 5 and 16 years) with intractable epilepsy underwent Wada testing before resective epilepsy surgery (93 within the left hemisphere, and 63 within the right hemisphere). Memory stimuli were presented soon after intracarotid amobarbital injection, and recognition memory for the items was assessed after return to neurologic baseline. Eighty-eight children underwent unilateral temporal lobe resection, and 68 had extratemporal lobe resections. One hundred four (67%) children were seizure free (Engel class I), and 52 (33%) were not seizure free (Engel classes II-IV) at follow-up (mean follow-up interval, 2.3 years). RESULTS: Seizure-free children recalled 19.3% more Wada memory items after ipsilateral injection than did non-seizure-free children (p = 0.008). If analysis was restricted to youngsters with temporal lobectomies (TLs), seizure-free children recalled 27.7% more items after ipsilateral injection than did non-seizure-free TL children (p = 0.004). With regard to individual patient prediction, 75% of children who had memory score asymmetries consistent with the seizure focus were seizure free. In contrast, only 56% of children whose memory score asymmetries were inconsistent with the seizure focus were seizure free (p = 0.01). CONCLUSIONS: Results suggest that Wada memory performance asymmetries are related to the degree of seizure relief after epilepsy surgery in children and adolescents.     

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.     

Endovascular ablation of a temporal lobe epileptogenic focus - a complication of Wada testing

The authors report on a patient with a long history of medically refractory temporal lobe epilepsy. During pre-operative evaluation for anterior temporal lobectomy he underwent a Wada test for speech and memory lateralization. During the procedure, he suffered a focal cerebral infarct, within the right medial temporal lobe, at the site of the epileptic focus. This resulted in the resolution of his seizure disorder. The possibility of endovascular management of seizure disorders of the temporal lobe should be investigated further as a potentially minimal invasive therapeutic option for medically intractable epilepsy.     

Evaluating the contributions of state-of-the-art assessment techniques to predicting memory outcome after unilateral anterior temporal lobectomy

PURPOSE: Although anterior temporal lobectomy (ATL) is an effective treatment for many patients with medically refractory temporal lobe epilepsy (TLE), one risk associated with this procedure is postsurgical decline in memory. A substantial number of past studies examined factors that predict memory decline after surgery, but few have investigated multiple predictors simultaneously or considered measures that are currently in use. METHODS: This study compared the relative contributions made by presurgical neuropsychological test scores, MRI-based hippocampal volumetric analysis, and Wada test results to predicting memory outcome after ATL in a group of 87 patients. RESULTS: Logistic regression analyses indicated that noninvasive procedures (neuropsychological testing and MRI) made significant contributions to improving the prediction of memory outcome in this sample. The results from the Wada procedure did not significantly improve prediction once these other factors were considered. The only exception was in predicting memory for visual information after a delay, in which Wada results improved prediction accuracy from 78% to 81%. CONCLUSIONS: Current neuropsychological tests and MRI volumetric measures predict changes in verbal and visual memory after ATL. The relatively small change in correct classification rates when Wada memory scores are considered calls into question the benefits of using Wada test results to predict memory outcome when the results of noninvasive procedures are available.     

Effect of Wada Memory Stimulus Type in Discriminating Lateralized Temporal Lobe Impairment

Summary: Purpose : To examine the effects of memory stimulus type on Wada memory performance.
Method : Ninety-six patients (left, 47; right, 49) from four epilepsy centers who were candidates for anterior temporal lobectomy (ATL) and who have subsequently undergone surgery were studied. Patients with atypical cerebral language lateralization or with evidence on magnetic resonance imaging (MRI) to suggest a lesion other than hippocampal sclerosis were excluded. Wada memory performance was obtained by using both real objects and line drawings as memory stimuli.
Results : Wada memory laterality scores with either real objects or line drawings as memory stimuli discriminated left from right-ATL groups. However, objects were superior to line drawings in making this differentiation. Further, objects were superior to line drawings in individual patient classification of candidates for left ATL, with no difference in the classification rates using either objects or line drawings in candidates for right ATL.
Conclusions : Type of memory stimuli is an important factor affecting memory results during the Wada test.     

Stimulus type affects Wada memory performance

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

Wada Memory Disparities Predict Seizure Laterality and Postoperative Seizure Control

Summary: We examined the efficacy of a memory difference score (DS: right minus left hemisphere memory) during the Wada test (intracarotid amobarbital procedure, IAP) for predicting seizure laterality and postoperative seizure outcome in 70 left speech dominant patients from two epilepsy centers. DS ≥2, after addition of 1 point to the left hemisphere injection score to account for aphasia, were noted in 71. 4% of patients and correctly predicted surgery side for 98. 0% of these patients. The DS related significantly to seizure outcome at 1–year follow-up (p < 0.002) and correctly predicted 80% of patients who were The Wada test, or intracarotid amobarbital procedure (IAP), is traditionally used to determine the laterality of language dominance and to assess the memory competence in the hemisphere contralateral to the proposed temporal lobectomy in an effort to avoid postoperative amnesia (1–6). Ipsilateral memory testing (adequacy of the hemisphere ipsilateral to anticipated resection) also is frequently examined. The validity of IAP memory testing as a measure of temporal lobe function is demonstrated by correlating IAP memory scores of the affected hemisphere with hippocampal cell counts (7,8) and with hippocampal volume assessed by magnetic resonance imaging (MRI) (9). The disparity between ipsilateral and contralateral memory scores is often predictive of seizure focus laterality (1 1–18). However, most studies have examined group means rather than the utility of the DS for predicting the seizure focus in specific patients. To date, only Loring et al. (9) have reported Presented in part at the Annual Meeting of the International Neuropsychological Society, Galveston, Texas, February 1993. seizure-free. Patients whose DS did not correctly predict seizure laterality more frequently required invasive studies to establish seizure onset. The relationship of the DS to laterality did not differ significantly by class of IAP memory stimuli. When seizures originate from the temporal lobe, the IAP memory DS predicts seizure laterality by assessing the functional adequacy of the involved hemisphere and is predictive of seizure control.     

Pre- and postoperative intracarotid amytal procedure: an assessment of validity

The intracarotid amytal procedure (IAP) was used twice to assess the suitability of three male patients for two successive neurosurgical procedures to relieve intractable temporal lobe epilepsy. First an amygdalohippocampectomy was performed, then further tissue was removed in a temporal lobe resection because their seizures had failed to remit. Repetition of the IAP following amygdalohippocampectomy when there was a known excision allowed inferences to be made regarding its validity in assessing lateralization of language functioning, memory functioning, and lateralization of seizure focus. The procedure was found to be reliable in assessing both language dominance and adequacy of memory functioning of the hemisphere contralateral to the lesion site. The procedure's third function of lesion lateralization was valid for identifying the known neurosurgical lesion. However, it was less successful in corroborating the lateralization of seizure focus before amygdalohippocampectomy. Differences in cognitive outcome between the two neurosurgical procedures are discussed.     

Feeling-of-knowing in temporal lobe epilepsy: monitoring knowledge inaccessible to conscious recall

Feeling-of-Knowing was compared in left temporal, right temporal, and control subjects. Seizure patients, like controls, demonstrate knowledge of information that is not accessible to conscious recall, but they are less accurate in FOK judgements. Furthermore, there are significant differences between seizure patients and controls in the relationship between Feeling-of-Knowing and object level memory scores: (1) Controls spend more time searching memory for inaccessible information that is correctly identified on a later recognition test than they do for information that is incorrectly recognized. (2) Latency of correct recognition decreases as strength of FOK increases among controls, suggesting that controls correctly anticipate the outcome of memory search. These patterns of performance, which are consistent with an efficient memory search termination device, were not observed among seizure patients. The findings suggest that inaccurate Feeling-of-Knowing may play a role in inefficient memory search mechanisms in temporal lobe epilepsy.     

Contribution of neuropsychology to epilepsy surgery

Surgical treatment is being used with increasing frequency for patients with intractable epilepsy. Operative success depends to a large degree on the results of a comprehensive pre-operative patient evaluation the main purpose of which is to delineate the epileptogenic lesion. The pre-operative assessment includes video EEG monitoring, structural and functional (fMRI) neuroimaging and neuropsychological evaluation. The likelihood of the success of surgery is increased when all test results point to a single epileptogenic focus. The unique contribution of neuropsychology, which includes standard neuropsychological assessment and intracarotid sodium amytal (Wada) testing, is its capability to predict lateralization and often localization of a brain lesion based on cognitive function and dysfunction, which can be demonstrated also in the absence of a structural lesion. The Wada test is used to determine the cerebral speech dominance, to predict postsurgical amnesia and is found to be useful in predicting laterality of seizure focus in candidates for temporal lobectomy.     

Risks and benefits of epilepsy surgery in a pediatric population: Consequences for memory and academic skills

We examined benefits and risks for memory and academic functioning associated with epilepsy surgery in a pediatric population. A total of 46 patients with intractable seizures and a single seizure focus were divided into four groups according to focus localization: right temporal, left temporal, frontal, and parietal/occipital region. Pre- and postsurgery performance measures were compared across groups and with a fifth group of patients that had intractable seizures but did not undergo surgery. Both groups with temporal lobe epilepsy showed significant declines in memory test scores, while performance of the group with frontal lobe epilepsy improved. These changes were mirrored in parental reports of everyday memory. Consistent with other pediatric studies, no lateralized material-specific declines in the groups with temporal lobe epilepsy were found. When memory improved, the improvement was associated with decreases in seizure frequency and the number of anticonvulsant medications. Presurgical performance was the best predictor of declines in memory test performance. Deterioration of academic test scores in the group that did not have surgery exemplified a potential risk of living with seizures and antiepilepsy medication.     

Memory lateralization in medial temporal lobe epilepsy assessed by functional MRI

PURPOSE: To determine the utility of functional magnetic resonance imaging (fMRI) in preoperative lateralization of memory function in patients with medial temporal lobe epilepsy (MTLE). METHODS: Nine patients with MTLE underwent standard preoperative assessment including video-EEG and intracarotid amytal testing (IAT). fMRI was performed while subjects encoded four types of stimuli (patterns, faces, scenes, and words). Activation maps were created for each subject representing areas more active for novel than for repeated stimuli. Regions of interest were drawn around the MTL in individual subjects, suprathreshold voxels were counted, and an asymmetry index was calculated. RESULTS: In eight of nine subjects, lateralization of memory encoding by fMRI was concordant with that obtained from the IAT. Group-level analysis demonstrated greater activation in the MTL contralateral to the seizure focus such that in the left MTLE group, verbal encoding engaged the right MTL, whereas in the right MTLE group, nonverbal encoding engaged the left MTL. CONCLUSIONS: fMRI is a valid tool for assessing of memory lateralization in patients with MTLE and may therefore allow noninvasive preoperative evaluation of memory lateralization. FMRI revealed that memory encoding may be reorganized to the contralateral MTL in patients with MTLE.     

Seizures During Cognitive Testing in Patients with Temporal Lobe Epilepsy: Possibility of Seizure Induction by Cognitive Activation

In 18 of 185 patients under consideration for epilepsy surgery, 20 seizures were observed during neuropsychological evaluation. We wished to determine whether the task at seizure onset corresponded neuropsychologically to lateralization of the epileptic focus. The patients' characteristics and the circumstances of the seizures were as follows: Fourteen patients had right temporal lobe epilepsy (RTE) and four had left temporal lobe epilepsy (LTE). Although a wide range of cognitive functions had been tested, all but one seizure occurred during assessment of memory performance. In the RTE patients, 12 of 16 seizures occurred during visual memory testing. Two seizures were observed during a verbal memory task, and one seizure was observed during mental rotation. In two LTE patients, seizures were elicited during verbal memory testing. Two LTE patients with seizures during visual memory testing had speech dominance of the right hemisphere. This high correspondence between the eliciting performance and the focus localization suggests that cognitive performances ipsilateral to the epileptic focus may affect seizure threshold in focal epilepsies.     

Interpretation of Wada memory test for lateralization of seizure focus by use of (99m)technetium-HMPAO SPECT

PURPOSE: Although the intracarotid amobarbital procedure (IAP) or Wada test is useful in lateralizing seizure focus in patients with temporal lobe epilepsy (TLE), the results of the IAP memory test are frequently nonlateralizing. An insufficient suppression of the medial temporal region contralateral to the seizure focus may contribute to the failure of lateralization. We tried to correlate IAP memory results with the functional changes in the contralateral medial temporal region as measured by single photon emission computed tomography (SPECT) during IAP. METHODS: We performed a (99m)technetium-(Tc) hexamethylene-propylene-amine-oxime (HMPAO) brain SPECT in 19 medial TLE patients during a contralateral IAP (sodium amobarbital injected contralateral to the seizure focus). Regional cerebral blood flow (rCBF) was measured in the contralateral medial temporal region. The amount of decrease in the rCBF was calculated by subtracting the previous measurement from the one obtained with the interictal SPECT. RESULTS: Ten (53%) patients passed and nine (47%) failed the contralateral IAP. The mean percentage decrease in rCBF was 5.3+/-5.3%. There was a significant negative correlation between a decrease in the rCBF and the IAP memory-retention score by Spearman correlation (p = -0.53: p<0.021). Patients with smaller decreases in rCBF (<5%) more frequently passed the contralateral IAP memory test than did those with larger decreases (80 vs. 22%; p<0.023). CONCLUSIONS: We suggest that an insufficient suppression of the contralateral medial temporal function is partly responsible for nonlateralizing IAP memory tests. An IAP-SPECT may be useful in interpreting IAP memory tests for the lateralization of seizure focus in TLE patients.     

Material-specific memory changes after anterior temporal lobectomy as predicted by the intracarotid amobarbital test

Summary: Purpose: The intracarotid amobarbital test (IAT) has been shown to predict verbal memory changes after anterior temporal lobectomy (ATL). Seeking to extend these findings, we examined two questions: (a) What is the relationship between material‐specific aspects of IAT memory and material‐specific memory changes after ATL? and (b) Which IAT memory score(s) optimally predict memory changes after surgery, the memory score after injection ipsilateral to the seizure focus, the memory score after injection contralateral to the seizure focus, or the IAT asymmetry score, comprising the ipsilateral minus contralateral injection scores? Methods: Seventy left hemisphere language‐dominant patients undergoing ATL for treatment of medically refractory seizures were administered a verbal and visuospatial recognition memory test before surgery and 3 weeks after surgery. IAT memory recognition scores for words and designs were used to predict verbal and visuospatial memory changes after surgery. Results: After surgery, left ATL patients declined in verbal memory, whereas right ATL patients declined in visuospatial memory. IAT total recognition memory scores (collapsed across all types of materials) and IAT word memory scores were associated with postoperative verbal memory decline. This relationship was significant for the IAT ipsilateral injection memory scores and the IAT hemispheric asymmetry scores. IAT memory performances were not related to visuospatial memory changes. Conclusions: Results indicate IAT memory measures to be related to postoperative verbal, but not visuospatial, memory change. A specific relationship was found between postoperative verbal memory change and IAT verbal memory after injection ipsilateral to the seizure focus, when relying primarily on the contralateral hemisphere. This finding is consistent with the functional reserve model of memory change in ATL.     

Effects of topiramate on memory performance on the intracarotid amobarbital (Wada) test

We evaluated the effects of topiramate (TPM) on memory function in the intracarotid amobarbital (Wada) test in nine patients with mesial temporal lobe epilepsy (MTLE) whose antiepileptic drugs (AEDs) included TPM and compared their scores with those of 16 patients with MTLE on AEDs not including TPM. Sodium amobarbital was injected first into the hemisphere ipsilateral to the seizure focus and then into a contralateral site, and the patients were tested for naming and memorization. There was no statistical difference in percentage memory scores between the two patient groups following the contralateral injection. After the ipsilateral injection, however, TPM patients had significantly lower percentage memory scores compared with non-TPM patients (P < 0.02). We conclude that a possible adverse effect of TPM on memory performance should be considered when evaluating the Wada test memory scores of patients on TPM therapy.     

Decline in Verbal Memory Associated with Duration of Epilepsy: An Intracarotid Amobarbital Study

Background. Many patients with mesial temporal sclerosis (MTS) observe that their memory has declined over time, but objective evidence for this is scant.Method. Verbal memory scores were obtained during amobarbital injection of the right carotid artery in 30 right-handed patients with right mesial temporal sclerosis and unilateral right temporal lobe seizures. These were compared with duration of epilepsy and seizure frequency. An estimate of the total number of lifetime seizures was formed by multiplying epilepsy duration by seizure frequency.Results. Verbal memory function in the left temporal lobe was negatively associated with longer duration of epilepsy (P < 0.05). There was a strong negative correlation between verbal memory and increased lifetime number of seizures (P < 0.01).Conclusion. This study provides evidence that seizures arising in the right temporal lobe lead to progressive dysfunction of memory functions in the contralateral side.     

Predictors of postoperative memory function after left anterior temporal lobectomy

Patients who undergo left anterior temporal lobectomy (ATL) for intractable epilepsy are at risk of postoperative memory decline. This study attempts to identify the best predictors of memory after ATL using preoperative tests. Thirty-two consecutive patients who underwent left ATL with preoperative and postoperative neuropsychological testing were retrospectively identified. The following independent variables were analyzed by multiple regression: age of onset of seizures, age of temporal lobe damage, gender, MRI results, preoperative memory testing, and intracarotid amytal procedure (IAP) results. Neuropsychological measures of verbal and nonverbal memory served as dependent variables. Male gender (P<0.005), failing the IAP with both left and right hemispheres (P<0.001), and higher logical memory (LM) scores preoperatively (P<0.001) were associated with greater declines in LM after surgery. Our data demonstrate that the IAP predicts postoperative memory independent of other factors known to affect memory after left ATL.