Depth electrode studies in temporal lobe epilepsy: relation to quantitative magnetic resonance imaging and operative outcome

Simultaneous scalp EEG improves seizure lateralization during unilateral intracranial EEG evaluation in temporal lobe epilepsy

PURPOSE

To determine if simultaneous bilateral scalp EEG (scEEG) can accurately detect a contralateral seizure onset in patients with unilateral intracranial EEG (IEEG) implantation.

METHODS

We evaluated 39 seizures from 9 patients with bitemporal epilepsy who underwent simultaneous scEEG and IEEG (SSIEEG). To simulate conditions of unilateral IEEG implantation with a missed contralateral seizure onset, we analyzed the IEEG recording contralateral to the seizure onset (CL- IEEG), in conjunction with simultaneous scEEG. The following criteria were evaluated between scEEG and CL- IEEG (1) latency: the time to onset of EEG seizure (2) location: concordance of ictal onset zones and (3) pattern: congruence of EEG morphology and frequency.

RESULTS

SSIEEG correctly lateralized 36/39 (92.3%) seizures compared to 13/39 (33.3%) seizures using CL- IEEG alone (OR = 24.0, p < 0.01), 33 (84.6%) seizures using scEEG alone (OR = 2.2, p = 0.29) and 26 (66.9%) seizures using time of clinical onset alone (OR = 6.0, p = 0.01). For the three criteria evaluated, (1) 22/39 (56.4%) seizures had an earlier onset on the scEEG, compared to CL- IEEG; (2) lack of congruence of location of seizure onset was noted in 33/39 (84.6%) of the seizures; and (3) 22/39 (56.4%) seizures did not have a congruent ictal pattern.

CONCLUSIONS

The chronological, topographic and morphologic features of SSIEEG can accurately detect the hemisphere of seizure onset in most cases with unilateral IEEG implantation. SSIEEG is significantly better than, IEEG, scEEG or clinical onset alone in this scenario. We propose that SSIEEG should be considered in all cases of intractable focal epilepsy undergoing unilateral IEEG evaluation.

Use of an intraventricular strip electrode for mesial temporal monitoring in children with medically intractable epilepsy

OBJECTIVE The objective of this study was to evaluate mesial temporal electroencephalographic (EEG) monitoring, using an intraventricular strip electrode (IVSE) along the ventricular surface of the hippocampus, in children with medically intractable epilepsy. METHODS The authors reviewed 10 consecutive cases in which subdural electrode placements and mesial temporal monitoring were recommended. The median age of the patients was 12.7 years (range 4.5-19.3 years). Both grids and IVSE were placed in all patients. The 4-contact IVSE was used in 5 cases, and the 6-contact IVSE in the other 5 cases. The median number of contacts, including IVSE contacts, was 122 (range 66-181). A total of 182 seizures were analyzed. RESULTS The IVSE localized seizure-onset zones in 8 patients. The seizure-onset zone was identified exclusively by IVSE in 3 patients and was simultaneous in IVSE and subdural electrodes in 5 patients. Among the 5 patients with simultaneous onset on both IVSE and subdural electrodes, 4 had basal temporal onset and one had orbitofrontal and lateral midtemporal onset. In the remaining 2 patients, the absence of IVSE seizure onset permitted sparing of mesial temporal structures. An Engel Class Ia outcome was achieved in 9 of 10 cases. No complication was associated with IVSE placement. CONCLUSIONS Intracranial monitoring using IVSE offers an alternative in terms of quality of EEG recording. IVSE was useful in children who already required open craniotomy for intracranial monitoring over an extensive network of hyper-excitability.

The Value of Diagnostic Bilateral Intracranial Electroencephalography in Treatment-Resistant Focal Epilepsy

OBJECTIVES

We assessed the efficacy and risks of diagnostic bilateral intracranial electroencephalography (bICEEG) in patients with treatment-resistant epilepsy (TRE) with poorly lateralized epileptogenic zone on noninvasive studies as reflected by progress to resection, Engel outcome, and complication rate.

METHODS

This is a retrospective chart review of 199 patients with TRE who had diagnostic bICEEG at New York University Medical Center between 1994 and 2013. Study end points were progress to resection, surgical outcome, and perioperative complications. Univariate analysis was performed with analysis of variance, t test, or Fisher exact test; multivariable analysis was performed using discriminant function analysis.

RESULTS

bICEEG lateralized the epileptogenic zone and the patient had resection in 60.3% of cases. The number of depth electrodes used was positively correlated with resection, and surgical complications during bICEEG negatively correlated. Vagal nerve stimulators were implanted in 58.2% of patients who did not undergo resection and 20.7% of those who did. Among the 87 patients who progressed to resection and had more than 1-year follow-up, 47.1% were seizure free compared with 12.7% of the 55 who did not. Male sex correlated with good postoperative seizure control. The most common complication was infection requiring debridement, occurring in 3.1% of admissions (9 of 290).

CONCLUSIONS

At our center, 60% of patients undergoing bICEEG progress to resection and 57% of these had more than 90% reduction in seizures. We conclude that bICEEG allows the benefits of epilepsy surgery to be extended to patients with poorly lateralized and localized TRE.

Quantitative MRI in refractory temporal lobe epilepsy: relationship with surgical outcomes

Medically intractable temporal lobe epilepsy (TLE) remains a serious health problem. Across treatment centers, up to 40% of patients with TLE will continue to experience persistent postoperative seizures at 2-year follow-up. It is unknown why such a large number of patients continue to experience seizures despite being suitable candidates for resective surgery. Preoperative quantitative MRI techniques may provide useful information on why some patients continue to experience disabling seizures, and may have the potential to develop prognostic markers of surgical outcome. In this article, we provide an overview of how quantitative MRI morphometric and diffusion tensor imaging (DTI) data have improved the understanding of brain structural alterations in patients with refractory TLE. We subsequently review the studies that have applied quantitative structural imaging techniques to identify the neuroanatomical factors that are most strongly related to a poor postoperative prognosis. In summary, quantitative imaging studies strongly suggest that TLE is a disorder affecting a network of neurobiological systems, characterized by multiple and inter-related limbic and extra-limbic network abnormalities. The relationship between brain alterations and postoperative outcome are less consistent, but there is emerging evidence suggesting that seizures are less likely to remit with surgery when presurgical abnormalities are observed in the connectivity supporting brain regions serving as network nodes located outside the resected temporal lobe. Future work, possibly harnessing the potential from multimodal imaging approaches, may further elucidate the etiology of persistent postoperative seizures in patients with refractory TLE. Furthermore, quantitative imaging techniques may be explored to provide individualized measures of postoperative seizure freedom outcome.

Selective amygdalohippocampectomy versus anterior temporal lobectomy in the management of mesial temporal lobe epilepsy: a meta-analysis of comparative studies

Object

Whether selective amygdalohippocampectomy (SelAH) has similar seizure outcomes and better neuropsychological outcomes compared with anterior temporal lobectomy (ATL) is a matter of debate. The aim of this study was to compare the 2 types of surgery with respect to seizure outcomes and changes in IQ scores.

Methods

PubMed, Embase, and the Cochrane Library were searched for relevant studies published between January 1990 and September 2012. Studies comparing SelAH and ATL with respect to seizure and intelligence outcomes were included. Two reviewers assessed the quality of the included studies and independently extracted the data. Odds ratios and standardized mean deviations with 95% confidence intervals were used to compare pooled proportions of freedom from seizures and changes in IQ scores between the SelAH and ATL groups.

Results

Three prospective and 10 retrospective studies were identified involving 745 and 766 patients who underwent SelAH and ATL, respectively. The meta-analysis demonstrated a statistically significant reduction in the odds of seizure freedom for patients who underwent SelAH compared with those who underwent ATL (OR 0.65 [95% CI 0.51–0.82], p = 0.0005). The differences between the changes in all IQ scores after the 2 types of surgery were not statistically significant, regardless of the side of resection.

Conclusions

Selective amygdalohippocampectomy statistically reduced the odds of being seizure free compared with ATL, but the clinical significance of this reduction needs to be further validated by well-designed randomized trials. Selective amygdalohippocampectomy did not have better outcomes than ATL with respect to intelligence.

Predictive factors for outcome of invasive video-EEG monitoring and subsequent resective surgery in patients with refractory epilepsy

OBJECTIVE

This is a descriptive study of patients who underwent invasive video-EEG monitoring (IVEM) at Ghent University Hospital. The aim of the study is to identify predictive factors for outcome of IVEM and resective surgery (RS). These factors may optimize the patient flow following the non-invasive presurgical evaluation towards IVEM and RS or other treatments.

PATIENTS AND METHODS

Over the past 16 years, 68/710 refractory epilepsy patients included in the presurgical evaluation protocol (M/F 41/27, mean age 33 years) underwent IVEM at Ghent University Hospital. Patient features and follow-up data were collected from the patients' medical files and the electronic patient database at the neurology and neurosurgery department. Predictive factors for IVEM outcome were identified by comparing features of patients with a positive IVEM outcome (i.e. ictal onset zone identification) and patients with a negative IVEM outcome. Predictive factors for RS outcome were identified by comparing features of patients with Engel class I and patients with Engel class II-IV outcome.

RESULTS

In 56/68 patients (82%) IVEM outcome was positive. The occurrence of a seizure-free interval in the patient's history and a non-localizing ictal scalp EEG in patients with a structural abnormality on MRI (p<0.05) were predictive factors for a negative IVEM outcome. 32/68 patients underwent RS. In 22/32 (70%) patients RS resulted in an Engel class I outcome. A structural abnormality on MRI was a predictive factor for a positive RS outcome in patients in whom a focal or regional focus was resected (p<0.05).

CONCLUSION

This study shows that IVEM identifies one or more ictal onset zone(s) in up to 80% of patients. The potential of IVEM to identify the ictal onset zone is unlikely in patients with a seizure-free interval in their medical history and a non-localizing ictal scalp EEG during the non-invasive presurgical evaluation. Half of these patients underwent RS with long-term seizure freedom in 70%. Patients with structural MRI lesions have the highest chance of seizure freedom. These findings may contribute to the optimization of patient management during both the invasive and non-invasive presurgical work-up.

Temporal lobe surgery in patients with normal MRI

PURPOSE OF REVIEW

The surgical approach to nonlesional temporal lobe epilepsy presents a significant challenge due to uncertainties regarding the extent of resection necessary to result in a seizure-free state. To outline an optimum surgical strategy, an understanding of the clinical and diagnostic presentation of mesial and lateral temporal epilepsy is required in order to properly characterize the location of the ictal onset zone. This review focuses on several methods used to identify this ictal onset zone, with emphasis on the impact each modality has on surgical outcome.

RECENT FINDINGS

Factors predicting an excellent surgical outcome include the presence of a discrete zone of low voltage fast activity and prolonged propagation time on the electroencephalogram, and the absence of metabolic dysfunction in the contralateral temporal lobe. Identifying epileptogenic regions in the temporal lobe using magnetic source imaging is a recent technique that has also yielded promising surgical outcomes. Recent prospective studies have shown that a temporal neocortical resection is very effective in providing a seizure free outcome given strict localization of the ictal onset zone to the lateral temporal region, highlighting the need for accurate characterization of mesial versus lateral nonlesional epilepsy.

SUMMARY

With accurate identification of the ictal onset zone with intracranial electroencephalography, a tailored temporal resection can yield excellent surgical results.

Mutually suppressive interrelations of symmetric epileptic foci in bitemporal epilepsy and their inhibitory stimulation

OBJECTIVES

The goal of this study is to analyze the suppressive interaction of symmetric temporal lobe epileptic foci, assess some failures of epilepsy surgery, and evaluate the possibility of terminating focal seizures with stimulation of symmetric epileptic foci.

MATERIALS AND METHODS

One hundred and twenty-nine intractable epilepsy patients (age range 6-53 years) with bitemporal epileptiform abnormalities in multiple scalp EEGs were evaluated with chronically implanted depth and subdural electrodes. Interelectrode coherence and power spectra were studied using internally developed software.

RESULTS

Bitemporal epileptic foci were found in 85/129 (66%) patients with reciprocal relations between these foci in 57/85 (67%) patients. Temporal lobectomy was performed for 67/85 patients. 12/67 patients became free of seizures (Engel's Class I), 32/67 improved (Classes II and III), and 23/67 did not improve. 14/23 patients demonstrated post-surgical activation of the contralateral temporal lobe epileptic focus. For 8/14 of these patients, the stereotactic cryoamygdalatomy was performed in the temporal lobe contralateral to the first surgery. 5/8 patients became free of seizures. It was found that stimulation of temporal lobe deep epileptic focus may terminate focal seizures in the contralateral symmetric structures.

CONCLUSION

A mutually suppressive relationship is one of variants of the interaction of symmetric epileptic foci. Some epilepsy surgery failures may be a result of post-surgical activation of the intact focus. The increase of coherence between both temporal lobes before the seizure onset of the seizure suggests the establishment of functional interrelations between two epileptic foci at an early, "hidden" phase of seizures, and may predict the direction of seizure spread. Mutually suppressive interrelations of symmetric epileptic foci might be employed for chronic therapeutic stimulation.

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

OBJECT

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

METHODS

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

CONCLUSIONS

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

The clinical and electrophysiological characteristics of temporal lobe epilepsy with normal MRI

Background and Purpose

To identify the clinical and electrophysiological characteristics of temporal lobe epilepsy (TLE) with normal MRI.

Methods

Twenty-six patients were diagnosed with TLE with normal MRI by stereotaxically implanted depth electrode EEG (SEEG) and quantitative MRI. We divided the patients into anterior or diffuse temporal groups by interictal EEG, into localized, hemispheric or non-lateralized onset groups by ictal scalp EEG, and into focal or regional onset groups by SEEG. The clinical and electrophysiological characteristics were compared with those of 25 TLE patients with unilateral hippocampal atrophy (HA) on MRI. Four patients of TLE with unilateral HA also underwent SEEG.

Results

Patients in the normal MRI group showed a significantly higher frequency of secondarily generalization (225±235, median 160 vs 68±48, median 50, p<0.05), shorter duration of epilepsy (16±10 yrs vs 25.9±7.8 yrs, p<0.001), and less favorable surgical outcome (50% vs 88%, p <0.05) than patients in the unilateral HA group. Also, patients with normal MRI frequently showed diffuse temporal (50% vs 20%, p<0.05) discharges on interictal EEG. The ictal seizure patterns of patients with normal MRI showed less localization to one temporal lobe on scalp EEG (28% vs 65%, p<0.001) and a higher frequency of regional onset on SEEG (68% vs 8%, p<0.001) than patients with unilateral HA.

Conclusions

The characteristics of TLE with normal MRI compared with TLE with unilateral HA are shorter duration of epilepsy, higher frequency of secondarily generalization, and less favorable surgical outcome, suggesting wider areas of temporal lobe involved compared with patients with unilateral HA.

Relative localizing value of amygdalo-hippocampal MR biometry in temporal lobe epilepsy

OBJECTIVES

The aims of the study were (i) to examine the localizing value of three MRI quantitative modalities (qMRI) currently used for the analysis of the hippocampus and amygdala in the context of pre-surgical screening and (ii) to propose a step-by-step protocol based on the sensitivity and performance of the different MR techniques.

METHODS

Ninety-two adults with chronic mesial temporal lobe epilepsy (TLE) of which 28 underwent amygdalo-hippocampal resection, and 34 age-matched controls were included in the study. High-resolution qMRI was performed at 1.5 T, including a tilted T1-weighted 3D-dataset for volumetry and four-echoes T2 relaxometry (both for hippocampus and amygdala quantifications) and multi-voxel spectroscopy [NAA/(Cho+Cre)] (exclusively in the hippocampus). Individual qMRI data were compared with electroencephalography regarding the localization of the epileptogenic area, with the neuropathological data and with postoperative outcome. MRI pathology was defined based on 99% confidence ellipses. Ten controls were used to assess the quantitative MRI intra- and inter-observer variability for all variables.

RESULTS

Volumetric measurements revealed unilateral damage in 77% of the patients, T2-relaxometry in 64% and spectroscopy in 53%. Additional measurements of the amygdalae (T2-relaxometry) allowed us to localize pathology that coexists with that of the hippocampus in 34%, and isolated unilateral amygdala damage in 8% of patients. Volumetry and T2-relaxometry (not spectroscopy) were associated with postoperative outcome, but accurate predictive models were computed based on hippocampal measures only. At least at 1-year follow-up, volumetry predicts outcome correctly in 100% of the cases, whilst T2-relaxometry classified 96.4% (27/28) of these patients. All operated patients had hippocampal sclerosis.

CONCLUSIONS

Hippocampal structural damage is equivocally depicted by spectroscopy. For diagnostic and pre-operative evaluation, hippocampal volumetry and T2-relaxometry provide maximal accuracy. Amygdala quantifications are irrelevant in the pre-operative evaluation but may be useful for diagnostic purposes. Of the three qMRI modalities tested, T2-relaxometry provided the best balance between diagnosis accuracy and time-efficiency to lateralize a sclerotic lesion on the majority of the patients. Cases that remain undecided after T2-relaxometry may benefit from additional measurements based on hippocampal volumetry.

Seizure and memory outcome following temporal lobe surgery: selective compared with nonselective approaches for hippocampal sclerosis

Object

The aim of this study was to compare seizure and memory outcome in patients with medically refractory mesial temporal lobe epilepsy due to hippocampal sclerosis (MTLE/HS) treated using an anterior temporal lobectomy (ATL) or a selective amygdalohippocampectomy (SA).

Methods

Surgical outcome data were prospectively collected for 2 to 11 years in 161 consecutive patients with MTLE/HS. Eighty patients underwent an ATL and 81 an SA. Seizure control achieved with each technique was compared using the Engel classification scheme. Postoperative memory testing was performed in 86 patients (53%). At the last follow up, 72% of the patients who had undergone an ATL (mean follow up 6.7 years) and 71% of those who had undergone an SA (mean follow up 4.5 years) were seizure free (Engle Class IA). Estimated survival in patients in Engel Classes I, IA, and I and II combined did not differ between the two surgical techniques. Preoperatively, 58% of the patients had verbal memory scores one standard deviation (SD) below the normal mean. One third of the patients with preoperative scores in the normal range worsened after surgery, although this outcome was not related to the surgical technique. In contrast, one third of those whose preoperative scores were less than −1 SD experienced improvement after surgery. Nine (18%) of the 50 patients whose left side had been surgically treated improved their verbal memory scores by more than one SD. Seven (78%) of these nine underwent an SA (p = 0.05).

Conclusions

Both ATL and SA can lead to similar favorable seizure control in patients with MTLE/HS. Preliminary data suggest that postoperative verbal memory scores may improve in patients who undergo selective resection of a sclerotic hippocampus in the dominant temporal lobe.

Re-examination of the value of localising aura sensations and lateralising interictal epileptiform discharges in view of structural lesions demonstrated by MRI

We examined the relationship between MRI lesions and electro-clinical findings with special attention to the localising value of aura sensations and the sides of interictal epileptiform discharges in 327 patients with symptomatic localisation-related epilepsy. As a result, while autonomic as well as psychic auras were correlated with temporal lesions, simple motor seizures were associated with extra-temporal ones. Within the group of patients with temporal lobe epilepsy, autonomic but not psychic auras concurred significantly more often with medial temporal structural lesions. Furthermore, there was a significant difference between concordance rates between sides of MRI lesions and EEG foci as a function of laterality: while the right-sided MRI lesions constantly showed ipsilateral EEG foci, EEG foci concurring with the left-sided MRI lesions proved to be often falsely lateralising. From these results, we assumed that lateral as well as medial temporal involvement is needed in the genesis of the psychic aura in contrast to the autonomic aura, which could be induced without lateral temporal involvement, and lesions in the left hemisphere are more apt to induce secondarily epileptogenic than those in the right hemisphere.

Vision of the future: initial experience with intraoperative real-time high-resolution dynamic infrared imaging. Technical note

High-resolution dynamic infrared (DIR) imaging provides intraoperative real-time physiological, anatomical, and pathological information; however, DIR imaging has rarely been used in neurosurgical patients. The authors report on their initial experience with intraoperative DIR imaging in 30 such patients. A novel, long-wave (8-10 microm), narrow-band, focal-plane-array infrared photodetector was incorporated into a camera system with a temperature resolution of 0.006 degrees C, providing 65,000 pixels/frame at a data acquisition rate of 200 frames/second. Intraoperative imaging of patients was performed before and after surgery. Infrared data were subsequently analyzed by examining absolute differences in cortical temperatures, changes in temperature over time, and infrared intensities at varying physiological frequencies. Dynamic infrared imaging was applied in a variety of neurosurgical cases. After resection of an arteriovenous malformation, there was postoperative hyperperfusion of the surrounding brain parenchyma, which was consistent with a loss of autoregulation. Bypass patency and increased perfusion of adjacent brain were documented during two of three extracranial-intracranial bypasses. In seven of nine patients with epilepsy the results of DIR imaging corresponded to seizure foci that had been electrocorticographically mapped preoperatively. Dynamic infrared imaging demonstrated the functional cortex in four of nine patients undergoing awake resection and cortical stimulation. Finally, DIR imaging exhibited the distinct thermal footprints of 14 of 16 brain tumors. Dynamic infrared imaging may prove to be a powerful adjunctive intraoperative diagnostic tool in the neurosurgical imaging armamentarium. Real-time assessment of cerebral vessel patency and cerebral perfusion are the most direct applications of this technology. Uses of this imaging modality in the localization of epileptic foci, identification of functional cortex during awake craniotomy, and determination of tumor border and intraoperative brain shift are avenues of inquiry that require further investigation.

Neuroimaging and the progression of epilepsy

Several lines of evidence can be used to try to answer the question of whether epilepsy is a progressive disease, and whether persistent seizures, or the underlying process itself, cause neuronal injury. The results of clinical studies have been inconclusive. Neuroimaging studies offer a quantitative approach. In patients with temporal lobe epilepsy, structural magnetic resonance imaging (MRI) has shown volume reductions ipsilateral to the epileptic focus in hippocampal and extrahippocampal regions; the former, in cross-sectional studies, increase with increasing epilepsy duration. Other factors associated with increasing hippocampal atrophy include a history of complex or prolonged febrile seizures, and generalized tonic-clonic seizure number. Positron emission tomography (PET) has shown supporting results. However, these studies have been cross-sectional rather than longitudinal. Preliminary results from prospective imaging studies using fluorodeoxyglucose PET and volumetric MRI show that patients with more recent seizure onset are less likely to have hypometabolism or volume loss than those with a long history of epilepsy. Alternate interpretations of these data include a possible progressive effect of epilepsy, or a tendency for patients with structural or functional findings at seizure onset to be more likely to develop uncontrolled epilepsy. In addition to the human studies that have been performed, parallel investigations in animal models using some of the same imaging techniques may help to unravel the factors associated with neuronal injury due to seizures, and aid in interpreting results of clinical studies.

Seizure outcome after temporal lobectomy: current research practice and findings

PURPOSE

The literature regarding seizure outcome and prognostic factors for outcome after temporal lobectomy is often contradictory. This is problematic, as these data are the basis on which surgical decisions and counseling are founded. We sought to clarify inconsistencies in the literature by critically examining the methods and findings of recent research.

METHODS

A systematic review of the 126 articles concerning temporal lobectomy outcome published from 1991 was conducted.

RESULTS

Major methodologic issues in the literature were heterogeneous definitions of seizure outcome, a predominance of cross-sectional analyses (83% of studies), and relatively short follow-up in many studies. The range of seizure freedom was wide (33-93%; median, 70%); there was a tendency for better outcome in more recent studies. Of 63 factors analyzed, good outcome appeared to be associated with several factors including preoperative hippocampal sclerosis, anterior temporal localization of interictal epileptiform activity, absence of preoperative generalized seizures, and absence of seizures in the first postoperative week. A number of factors had no association with outcome (e.g., age at onset, preoperative seizure frequency, and extent of lateral resection).

CONCLUSIONS

Apparently conflicting results in the literature may be explained by the methodologic issues identified here (e.g., sample size, selection criteria and method of analysis). To obtain a better understanding of patterns of long-term outcome, increased emphasis on longitudinal analytic methods is required. The systematic review of possible risk factors for seizure recurrence provides a basis for planning further research.

T2 relaxometry can lateralize mesial temporal lobe epilepsy in patients with normal MRI

In unselected patients with intractable temporal lobe epilepsy (TLE), approximately 15% do not have detectable hippocampal atrophy on MRI. The purpose of this study was to evaluate whether T2 relaxometry can identify hippocampal pathology and lateralize the epileptic focus in patients with intractable TLE, who do not demonstrate hippocampal atrophy on volumetric MRI (MRIV). We selected 14 patients with unilateral TLE who had unilateral atrophy and 11 patients with unilateral TLE who had no evidence of atrophy on MRIV. Images were acquired on a 1.5 T MR scan using a dual echo sequence with 23 contiguous oblique coronal slices in all patients and in 14 healthy subjects. Fitting a single exponential decay equation to the imaging data generated T2 maps. Averages of six slices containing the head, body, and tail of the hippocampus were used to calculate hippocampal T2 relaxation times (HT2). The epileptic focus was defined by history, video-EEG, and surgical response. All TLE patients with hippocampal atrophy and 9/11 (82%) patients with normal MRI had abnormally high HT2 ipsilateral to the epileptic focus. Bilateral abnormal HT2 were found in 6/14 (43%) of patients with unilateral hippocampal atrophy and 2/11 (18%) of patients with normal MRI. However, this increase was always greater ipsilateral to the epileptic focus. Qualitative hippocampal pathology showed gliosis and neuronal loss in 10/14 operated patients with hippocampal atrophy on MRIV and in 5/7 operated patients with normal MRI. In conclusion, hippocampal T2 mapping provides evidence of hippocampal damage in the majority of patients with intractable TLE who have no evidence of atrophy on MRI and can correctly lateralize the epileptic focus in most patients.

Results of surgery in patients with bilateral independent temporal lobe spiking (BITLS) with normal MRI or bilateral mesial temporal sclerosis (MTS) investigated with bilateral subdural grids

PURPOSE

The introduction of new technologies in the clinical practice have greatly decreased the number of patients submitted to invasive recordings. On the other hand, some patients with refractory temporal lobe epilepsy have normal MR scans or bilateral potentially epileptogenic lesions. This paper reports the results of invasive neurophysiology and surgical outcome in such patients.

METHOD

Sixteen patients were studied. Eleven had normal MRI (Group I) and five had bilateral mesial temporal sclerosis (Group II). All patients had BITLS and non-localizatory seizures on video-EEG monitoring. All patients were implanted bilaterally with 32-contacts subdural grids. They were submitted to a cortico-amygdalo-total hippocampectomy at the side defined by chronic electrocorticography (ECoG).

RESULTS

In Group I, seizures came from a single side in nine patients. In nine patients, seizures started at one side, spread to the ipsolateral contacts and contralaterally afterwards. On the other hand, in two Group I patients seizures started in one mesial region and spread to the contralateral parahippocampus and neocortex before spreading to ipsolateral contacts. All patients in Group II had seizures starting unilaterally with focal EcoG onset in the mesial regions. Eight Group I patients are seizure-free and three are in Engel's class II. Eighty percent of Group II patients are seizure-free after surgery and one patient is in Engel's class II.

CONCLUSION

Good surgical results can be obtained in patients with BITLS. Patients with normal MRI seem to have a worse prognosis when compared to patients with unilateral or even bilateral MTS. Extensive subdural coverage is essential in patients with normal MRI.

Prognostic implication of contralateral secondary electrographic seizures in temporal lobe epilepsy

PURPOSE

Interhemispheric propagation of seizures in temporal lobe epilepsy is frequently noted during intracranial EEG monitoring. We hypothesized that a distinct secondary electrographic seizure (DSES) in the temporal lobe contralateral to primary seizure onset may be an unfavorable prognostic indicator.

METHODS

We reviewed intracranial depth electrode EEG recordings, 1-year outcome, and medical records of 51 patients (M 29, F 22: age 15-64 years) who underwent anterior temporal lobectomy during 1988-96. We defined DSES as a seizure that spread to the contralateral temporal lobe and produced distinct contralateral EEG features. The distinct feature was focal involvement of one or two electrode contacts at onset, which starts and evolves independently from the ipsilateral temporal lobe. We considered DSES as the predominant seizure pattern when it occurred in more than one half of the patients' recorded seizures.

RESULTS

Only nine of 19 (47%) patients with predominant DSES had a 1-year seizure-free outcome, whereas 27 of 32 (84%) patients without predominant DSES had a 1-year seizure-free outcome (p < 0.01). Bitemporal independent seizures were more common in patients with predominant DSES (9/19 versus 0/32; p < 0.001).

CONCLUSION

Our results suggest that distinct contralateral secondary electrographic seizure is a predictor of unfavorable outcome and is also more likely to be associated with bitemporal seizures.

Integration of EEG, MRI, and SPECT in localizing the seizure focus for epilepsy surgery

Several modalities are now available for detecting the structural and the functional abnormalities of a seizure focus. This article discusses the principles and techniques that can be used to integrate the data derived from different test modalities in delineating the seizure focus in epilepsy surgery candidates. An approach in integrating EEG, MRI, and SPECT abnormalities is described to demonstrate how the spatial relationships among them can be precisely determined by coregistering images of the abnormalities on the MRI. The recently developed technique of subtraction ictal SPECT coregistered to MRI (SISCOM) can reveal a discrete hyperperfusion focus with its relationship to the cerebral anatomy. The SISCOM focus can also serve as a target for intracranial electrode implantation and for subsequent surgical resection. This can be achieved by using a computer-based system of relating the image space to the surgical field. The limitations of each test in localizing the surgical seizure focus must be recognized when the value of each test is interpreted relative to those of other tests. In many patients, not all tests will show localizing abnormalities, and the foci determined by different tests may be incongruent. When the location of the focus is not compatible with the possible origin of the patient's habitual seizures, further evaluation with other tests, including intracranial EEG recordings, is necessary. The decision in determining which tests and how many to employ for localizing the surgical focus must be individualized for each patient.

Temporal lobe epilepsy: when are invasive recordings needed?

Temporal lobe epilepsy (TLE) is the most common type of medically intractable partial epilepsy amenable to surgery. In the majority of cases, the underlying pathology in temporal lobe epilepsy is mesial temporal sclerosis (MTS). Whereas historically invasive recordings were required for most epilepsy surgeries, indications have dramatically changed since the introduction of high-resolution MRI, which uncovers structural lesions in a high percentage of cases. No invasive recordings are required to perform a temporal lobectomy in patients with intractable epilepsy who have structural imaging suggesting unilateral MTS and concordant interictal and ictal surface EEG recordings, functional imaging, and clinical findings. Invasive testing is needed if there is evidence of bitemporal MTS on structural imaging and/or electrophysiologically, and additional information from functional imaging, neuropsychology, and the intracarotid amobarbital (Wada) test also does not help to lateralize the epileptogenic zone. Depth electrodes can be particularly helpful in this setting. However, no surgery is indicated, even without invasive recordings, if bitemporal-independent seizures are recorded by surface EEG and all additional testing is inconclusive. Other etiologies of TLE such as a tumor, vascular malformation, encephalomalacia, or congenital developmental abnormality account for about 30% of all patients who undergo epilepsy surgery. Epilepsy surgery is indicated after limited electrophysiologic investigations if neuroimaging and electrophysiology converge. However, approaches for resection in lesional temporal lobe epilepsy vary among centers. Completeness of resection is crucial and invasive recordings may be needed to guide the resection by mapping eloquent cortex and/or to determine the extent of the non-MRI-visible epileptogenic area. Specific approaches for the different pathologies are discussed because there is evidence that the relationship between the lesions visible on MRI and the epileptogenic zone varies among lesions of different pathologies, and therefore variable surgical strategies must be applied.

Paradigms for subdural grids' implantation in patients with refractory epilepsy

RATIONALE

The need for invasive monitoring in patients with refractory epilepsy has been greatly reduced by the introduction of new technologies such as PET, SPECT and MRI in the clinical practice. On the other hand, 10 to 30% of the patients with refractory epilepsy have non-localizatory non-invasive preoperative work-up results. This paper reports on the paradigms for subdural electrodes implantation in patients with different refractory epileptic syndromes.

METHODS

Twenty-nine adult refractory epileptic patients were studied. Patients were divided into five different epileptic syndromes that represented the majority of the patients who needed invasive recordings: bitemporal (Group I; n=16 ), bi-frontal-mesial (Group II, n=5), hemispheric (Group III; n=2), anterior quadrant (Group IV; n=3) and posterior quadrant (Group V; n=3). All of them were submitted to extensive subdural electrodes' implantation (from 64 to 160 contacts) covering all the cortical surface potentially involved in epileptogenesis under general anesthesia.

RESULTS

All patients tolerated well the procedure. There was no sign or symptom of intracranial hypertension except for headache in 22 patients. In all except one Group II patient, prolonged electrocorticographic monitoring using the described subdural cortical coverage patterns was able to define a focal area amenable for resection. In all Groups II-V patients cortical stimulation was able to adequately map the rolandic and speach areas as necessary.

CONCLUSION

Despite recent technological advances invasive neurophysiological studies are still necessary in some patients with refractory epilepsy. The standardization of the paradigms for subdural implantation coupled to the study of homogeneous patients' populations as defined by MRI will certainly lead to a better understanding of the pathophysiology involved in such cases and an improved surgical outcome.

Invasive electrographic recording techniques in temporal lobe epilepsy

The management of uncontrolled partial epilepsy is a process dependent on a multidisciplinary and analytic approach. It is necessary to understand which lesions are epileptogenic, and if they are indeed responsible for the generation of seizures. In addition to localizing seizure onset, the functional and eloquent areas of the brain need to be identified. As in many other centres, we perform resective surgeries on the basis of combined information derived from seizure semiology, EEG abnormalities, neuroimaging and other tests of cerebral function. If surface EEG recording yields inconclusive or ambiguous results, then invasive intracranial techniques using intracerebral depth or subdural electrodes can be used to improve diagnostic or prognostic accuracy. The indications, principles, results and complications of these recording techniques based on extensive experience at two epilepsy surgery centres are reviewed.

The EEG evaluation of single photon emission computed tomography abnormalities in epilepsy

Single photon emission computed tomography (SPECT) has increasingly been used as a diagnostic procedure for localizing epileptic seizure foci and as a research tool for investigating the physiologic mechanisms underlying seizure activity. With increasing use of SPECT in localizing the seizure focus for epilepsy surgery, there arises a need to critically assess its current role in the evaluation of patients for epilepsy surgery, especially as it relates to other clinical and laboratory data used in presurgical evaluation. Ictal EEG discharge has traditionally been used as the "gold standard" against which SPECT studies are compared in assessing the latter's localizing value. However, this practice presents a major challenge because SPECT studies are often reserved for patients with nonlocalizing EEG or magnetic resonance imaging findings. Nonetheless, SPECT studies in evaluation for epilepsy surgery should always be performed with the knowledge of the patient's EEG activity preceding, during, and after the injection of the radiotracer. The advent of techniques such as subtraction SPECT with co-registration on magnetic resonance imaging (SISCOM) and computer image-guided surgery has great potential in enhancing the clinical electrophysiologic evaluation of SPECT-detected abnormalities in epilepsy. These techniques permit accurate spatial correlation between intracranial EEG activity and SPECT perfusion patterns. The techniques can also be used to evaluate the effect of the extent of EEG focus resection compared with that of SISCOM focus resection to determine which has more prognostic importance in postsurgical control of seizures. Both animal and human studies are warranted to advance our knowledge of the electrophysiology associated with the various SPECT perfusion patterns.

White-matter change in mesial temporal sclerosis: correlation of MRI with PET, pathology, and clinical features

PURPOSE

To assess the magnetic resonance imaging (MRI), positron emission tomography (PET), pathology, and clinical findings of patients with the MRI feature of white-matter change (WMC) in the anterior temporal lobe.

METHODS

Fifty-six patients with pathologically proven mesial temporal sclerosis were included in this study. MRI and 18F-2-deoxyglucose-(FDG) PET images were obtained before surgery in all patients. The patients were divided into two groups according to the presence of WMC on their MRI. WMC consists of an indistinct gray-white matter demarcation and an increased signal intensity of the anterior temporal lobe on T2-weighted images. The two groups were then compared in terms of MRI, PET, pathology, and clinical features.

RESULTS

The MRI feature of WMC was observed in 18 (32%) of the 56 patients. PET images of those patients revealed more severe hypometabolism of the ipsilateral temporal lobes (p< 0.05). In terms of histologic findings, larger numbers of heterotopic neurons were observed in the anterior temporal lobe white matter of these patients who also shared the following clinical features: earlier seizure onset, frequent history of febrile convulsions, and favorable surgical outcomes.

CONCLUSIONS

The MRI feature of WMC is an additive sign for correct seizure lateralization and may be related to a favorable surgical outcome in patients with temporal lobe epilepsy.

Intracranial EEG in temporal lobe epilepsy

Intracranial EEG monitoring before epilepsy surgery, while becoming less commonly performed in patients with unilateral mesial temporal lobe epilepsy, is still widely used when bilateral independent temporal lobe seizures are suspected or when extratemporal foci cannot be ruled out by noninvasive means. Additionally, many epilepsy centers are reporting excellent surgical outcome in patients with neocortical temporal lobe epilepsy, when resections are guided by intracranial EEG studies. This article reviews the indications, technical aspects, risks, and interpretation of intracranial EEG in patients with temporal lobe seizures. It also considers intracranial EEG features predictive of surgical outcome.

[18F]FDG-PET and whole-scalp MEG localization of epileptogenic cortex

PURPOSE

To evaluate combined [18F]fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) and 122-channel whole-scalp magnetoencephalography (MEG) in lateralizing the epileptogenic cortex in patients whose routine presurgical evaluations gave discordant results about the location of the epileptic focus.

METHODS

Nine patients (five women, four men) aged 13-40 years were studied. Subdural EEG (SEEG) was recorded from eight patients. Six patients were operated on.

RESULTS

In seven of nine patients, PET and MEG agreed in localizing the epileptogenic cortex. When PET and MEG were in congruence, SEEG agreed with the findings. In five of six operated-on patients, PET and MEG results were congruent, and the outcome of the operation was successful. Two patients had discordant PET and MEG results. In one patient, PET showed bitemporal hypometabolism, whereas MEG showed epileptiform activity in the right parietal lobe. The surgical outcome of the palliative temporal lobectomy was poor. Another patient had unilateral temporal hypometabolism in PET and bitemporal activity in MEG. She was not operated on.

CONCLUSIONS

In most patients, PET and MEG were congruent in locating the epileptogenic cortex. Thus the combination of these techniques may provide useful support for the localization of the seizure onset and reduce the need for invasive procedures.

Chronic intracranial EEG monitoring for localizing the epileptogenic zone: an electroclinical correlation

PURPOSE

To evaluate the diagnostic yield and identify predictive factors of the surgical outcome in patients with intractable partial epilepsy undergoing chronic intracranial EEG monitoring (CIEM).

METHODS

The clinical, magnetic resonance imaging (MRI) and electrophysiologic data of 108 patients that underwent CIEM were retrospectively reviewed. The discharge pattern and spatial extent of the initial ictal discharge were determined by blinded visual inspection and computerized analysis.

RESULTS

The main predictive indicator for epilepsy surgery outcome in patients that underwent CIEM was the presurgical MRI findings. Most patients with hippocampal atrophy or complete lesionectomy were rendered seizure free after epilepsy surgery (83 and 80%, respectively), whereas only a small minority of patients with partial lesionectomy or no detected MRI lesion had seizure-free operative outcomes (21 and 22%, respectively). Multifocal independent initiation of the initial ictal discharge was associated with a poor surgical outcome. In contrast, the pattern and local spatial extent of the initial ictal discharge observed with CIEM failed to predict the surgical outcome.

CONCLUSIONS

The main predictor of the surgical outcome in patients that underwent CIEM was the MRI findings, whereas CIEM had only limited use in localizing the epileptogenic zone in the absence of an MRI lesion. The reported findings indicate a low specificity of CIEM in defining the site of seizure onset, which in turn significantly impairs the reliability of CIEM in delineating the epileptogenic zone for epilepsy surgery. Further studies are required to define the indications and patient subpopulations who can benefit from CIEM before epilepsy surgery.

Comparison of combined versus subdural or intracerebral electrodes alone in presurgical focus localization

PURPOSE

The yield of subdural versus intracerebral electrodes for ictal localization remains a point of controversy. We assessed the relative sensitivity of these two types of electrodes per case.

METHODS

Eighty-three intracranial recordings obtained from 82 patients were retrospectively reviewed to establish which type of electrode performed best in which patients and which seizure types.

RESULTS

Sixty (73%) of 82 patients had temporal lobe seizure onsets, eight frontal, nine widespread or multifocal/multilobar or both, whereas in five, seizure onset was not localized. Exclusive use of intracerebral electrodes would have been sufficient for accurate localization of the seizure-onset zone in all 35 patients with strictly mesial temporal seizure onsets. In only 20 (57%) of these 35 patients, the same decision would have been reached with exclusive use of subdural electrodes. In widespread neocortical and mesial temporal seizures (n = 25), yield of both electrode types was at about the same level, but neither was sufficient to identify the zone of ictal onset on its own. In frontal or multilobar seizures (n = 22), yield of subdural electrodes was slightly better then that of the intracerebral electrodes, but was not sufficient in all cases.

CONCLUSIONS

This study indicates that, depending on the characteristics of the seizure disorder, exclusive use of either intracerebral or subdural electrodes may easily result in erroneous diagnosis because of insufficient sampling of the brain. These findings are in contrast with other studies emphasizing the high yield of reliable EEG findings in evaluations with a single type of electrode and corroborate the results of one of our previous studies.

Temporal ictal electroencephalographic frequency correlates with hippocampal atrophy and sclerosis

We studied 328 complex partial seizures (CPS) in 63 consecutive patients with temporal lobe epilepsy who underwent scalp electroencephalography/video monitoring, magnetic resonance imaging (MRI), and surgery. The initial ictal discharge (IID), defined as the first sustained electrical seizure pattern localized to the surgical site, was determined. If the IID was rhythmic waves, the median frequency was measured. To determine if IID frequency correlates with hippocampal atrophy (HA) or sclerosis (HS), hippocampal volume ratios (HVRs) were measured (n = 52) or assessed visually (n = 11) on MRI, and mesial temporal histopathology specimens (n = 22) were graded for HS. Sixteen patients (25%) had no or mild HA (HVR = 0.78-1.02), and 47 patients (75%) had moderate-to-marked unilateral (HVR = 0.33-0.76), or bilateral, HA. Theta frequency IIDs were significantly more commonly associated with moderate-to-marked HA than were delta IIDs. Theta frequency IIDs occurred in 19% of patients with mild or no HA, and 79% of patients with moderate-to-marked HA; delta IIDs occurred in 63% of patients with little to no HA, and 13% of those with moderate-to-marked HA. In addition, the median IID frequency inversely correlated with HVR and directly correlated with HS severity. In conclusion, faster frequency rhythmic IIDs during temporal lobe CPS correlate with greater degrees of ipsilateral HA on MRI, and higher grades of HS.

Characterization and comparison of local onset and remote propagated electrographic seizures recorded with intracranial electrodes

PURPOSE

To compared the ictal discharge patterns between local onset and remote propagated electrographic seizures recorded with chronic intracranial electrodes.

METHODS

The electrophysiological data from 88 consecutive patients who underwent chronic intracranial EEG monitoring were retrospectively reviewed. The early and late discharge patterns of electrographic seizures at local onset and distant propagated sites were determined by blinded visual inspection and computerized analysis.

RESULTS

Four early and three late electrographic seizure patterns were observed at the local onset sites. The four early patterns consisted of a rhythmic discharge in the beta range ("beta buzz"), rhythmic alpha-theta activity, rhythmic sharp waves in the delta range, and an irregular spike discharge. The three distinct late-discharge patterns consisted of a late beta buzz, rhythmic sharp theta activity, and a rhythmic polyspike and wave discharge. At remote propagated sites, electrographic seizures could be divided into two different types according to their early discharge pattern. The first was unique to remote propagated electrographic seizures and consisted of a rhythmic theta-delta activity correlated with the concurrent activity at the local-onset site. The second remote initiation type consisted of patterns indistinguishable from the earlier discharge patterns recorded at the local onset site.

CONCLUSIONS

The initial ictal discharge pattern recorded with intracranial electrodes can assist in differentiating local onset and remote propagated electrographic seizures, with rhythmic round theta-delta activity being unique to distant propagated sites. Nevertheless, the initial discharge of a subclass of remote propagated electrographic seizures consists of an independent pattern indistinguishable from that observed at local onset sites.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Relations between EEG seizure morphology, interhemispheric spread, and mesial temporal atrophy in bitemporal epilepsy

PURPOSE

A strong relation exists between lateralization of seizure onset in temporal-lobe epilepsy and atrophic mesial structures measured by volumetric magnetic resonance imaging (MRI). We examined whether this relation extended to subregions of the mesial temporal lobe and whether the trend for seizures to spread contralaterally could be related to the localization of atrophy.

METHODS

We analyzed 362 seizures (with and without clinical signs) from 23 patients having bitemporal epilepsy in whom intracerebral electrodes were implanted for presurgical evaluation. Patients had measurements of hippocampal and amygdala volumes, including comparison with normal controls. We assessed on EEG the lateralization and localization of seizure onset and the trend to spread to the contralateral side (proportion of seizures that spread for each patient). We included all seizures, independent of the presence of clinical manifestations. These features were related to presence and localization of atrophy.

RESULTS

Among the 19 patients with mesial atrophy, agreement between side of prevalent seizure onset and predominant atrophy was found in 10 (53%). From 99 seizures starting in a temporal lobe with atrophy limited to the hippocampus, 67% started simultaneously in amygdala and hippocampus, 20% in hippocampus, and 13% in amygdala. From 137 seizures starting in a temporal lobe with amygdala and hippocampal atrophy, 47% started in amygdala and hippocampus, 48% in hippocampus, and 5% in amygdala. The trend to spread was 45% to the most atrophic side and 62% to the normal or less atrophic side.

CONCLUSIONS

When examining amygdala and hippocampus in this group of patients with bitemporal epilepsy, regions of seizure onset did not correspond to regions of predominant atrophy. The likelihood that seizures spread contralaterally was not influenced by atrophy in the region targeted by the spread. Precise relation between mesial temporal atrophy and seizures remain to be elucidated.

FDG-positron emission tomography and invasive EEG: seizure focus detection and surgical outcome

PURPOSE

To study the value of [18F]2-deoxyglucose (FDG)-positron emission tomography when surface ictal EEG is nonlocalizing.

METHODS

FDG-PET scans were performed in 46 patients with complex partial seizures (CPS) not localized by ictal surface-sphenoidal video-EEG (VEEG) telemetry. Interictal PET was performed with continuous EEG monitoring, and images were analyzed with a standard template. Forty patients subsequently had subdural and 6 had depth electrodes (invasive EEG, IEEG); 22 had bilateral implants. A focus was detected in 40, and 35 had temporal lobectomy based on IEEG localization.

RESULTS

There was a close association between IEEG and PET localization (p < 0.01): 26 patients had relative unilateral temporal FDG-PET hypometabolism, all had congruent IEEG, and 18 of 23 were seizure-free after temporal lobectomy. Five patients had unilateral frontotemporal hypometabolism (3 of 5 were seizure-free), 1 had frontal hypometabolism, and 14 had no lateralized PET abnormality (4 of 7 were seizure-free). Patients who became seizure-free had significantly higher lateral temporal asymmetry index (AI). PET showed > or = 15% relative temporal hypometabolism (AI) in 12 of 22 patients with nonlateralized surface ictal VEEG and was capable of distinguishing between frontal and temporal foci in 16 of 24 patients with lateralized, but not localized, surface ictal video-EEG.

CONCLUSIONS

FDG-PET provides valuable data in patients with unlocalized surface ictal EEG and can reduce the number of patients who require IEEG studies. Quantitation is necessary for optimal PET interpretation.

Significance of spikes at temporal lobe electrocorticography

Among 87 consecutive patients operated on under local anesthesia, few aspects of pre- and posttemporal lobe resection electrocorticograms (ECoG) yielded prognostic data. Preresection spikes were most common in the hippocampus, followed in order of frequency by the anterior temporal convexity and the inferior temporal surface. Moderately frequent (>10 spikes/100 s) preresection spikes appeared beyond the subsequent resection line in the posterior temporal region in 16 of 87 (18%) and in orbital frontal cortex in 12 of 87 (14%). Although many hippocampus spikes portended a favorable outcome and rare spikes an unfavorable one, preresection spike quantity otherwise failed to distinguish outcome groups. Absolute quantity of postresection spikes and change from preresectrion quantity in any region did not correlate with outcome except for the insula, where relatively abundant spikes portended favorable outcomes. Postresection electrographic seizures were rare but occurred equally in all outcome groups. No significant change in spike incidence occurred between the first and last 10-min epoch of the 30-min postresection recording.