Significance of Simple Partial Seizures in Temporal Lobe Epilepsy

Summary: We determined how localization of simple partial seizures (SPS) correlated with localization of complex partial seizure (CPS) in scalp/sphenoidal EEG and assessed prognosis after temporal lobe resective surgery in patients with an ictal correlate of SPS in scalp/sphenoidal EEG recordings. EEGs were recorded with the 10–20 system of electrode placement and supplemented with sphenoidal electrodes. Between 1985 and 1992, 183 patients with temporal lobe epilepsy (TLE) reported an aura (SPS) during inpatient monitoring; all were eligible for inclusion in our study. The EEGs during SPS showed ictal changes in 51 patients (28%, 117 SPS). Forty-four patients had unilateral temporal interictal spikes (IIS), and SPS and CPS always arose from the same region. Seven patients had bitemporal interictal spikes; SPS colocalized with CPS in 4 patients (57%), SPS were contralateral to CPS in 2 patients, and 1 patient had bilateral independent CPS but unilateral SPS. SPS accompanied by EEG ictal changes conveyed a favorable prognosis in patients who underwent epilepsy surgery. Scalp/sphenoidal recorded IIS but were less reliable in identifying the location of CPS onset in patients with bitemporal spikes.     

Lateralizing and localizing values of ictal onset recorded on the scalp: evidence from simultaneous recordings with intracranial foramen ovale electrodes

PURPOSE: The value of scalp recordings to localize and lateralize seizure onset in temporal lobe epilepsy has been assessed by comparing simultaneous scalp and intracranial foramen ovale (FO) recordings during presurgical assessment. The sensitivity of scalp recordings for detecting mesial temporal ictal onset has been compared with a "gold standard" provided by simultaneous deep intracranial FO recordings from the mesial aspect of the temporal lobe. As FO electrodes are introduced via anatomic holes, they provide a unique opportunity to record simultaneously from scalp and mesial temporal structures without disrupting the conducting properties of the brain coverings by burr holes and wounds, which can otherwise make simultaneous scalp and intracranial recordings unrepresentative of the habitual EEG. METHODS: Simultaneous FO and scalp recordings from 314 seizures have been studied in 110 patients under telemetric presurgical assessment for temporal lobe epilepsy. Seizure onset was identified on scalp records while blind to recordings from FO electrodes and vice versa. RESULTS: Bilateral onset (symmetric or asymmetric) was more commonly found in scalp than in FO recordings. The contrary was true for unilateral seizure onset. In seizures with bilateral asymmetric onset on the scalp, the topography of largest-amplitude scalp changes at onset does not have localizing or lateralizing value. However, 75-76% of seizures showing unilateral scalp onset with largest amplitude at T1/T2 or T3/T4 had mesial temporal onset. This proportion dropped to 42% among all seizures with a unilateral scalp onset at other locations. Of those seizures with unilateral onset on the scalp at T1/T2, 65.2% showed an ipsilateral mesial temporal onset, and 10.9% had scalp onset incorrectly lateralized with respect to the mesial temporal onset seen on FO recordings. In seizures with a unilateral onset on the scalp at electrodes other than T1/T2, the proportions of seizures with correctly and incorrectly lateralized mesial temporal onset were 37.5 and 4.2%, respectively. Thus the ratio between incorrectly and correctly lateralized mesial temporal onsets is largely similar for seizures with unilateral scalp onset at T1/T2 (16.7%) and for seizures with unilateral scalp onset at electrodes other than T1/T2 (11.2%). The onset of scalp changes before the onset of clinical manifestations is not associated with a lower proportion of seizures with bilateral onset on the scalp, or with a higher percentage of mesial temporal seizures or of mesial temporal seizures starting ipsilateral to the side of scalp onset. In contrast, the majority (78.4%) of mesial temporal seizures showed clinical manifestations starting after ictal onset on FO recordings. CONCLUSIONS: A bilateral scalp onset (symmetric or asymmetric) is compatible with a mesial temporal onset, and should not deter further surgical assessment. Although a unilateral scalp onset at T1/T2 or T3/T4 is associated with a higher probability of mesial temporal onset, a unilateral onset at other scalp electrodes does not exclude mesial temporal onset. A unilateral scalp onset at electrodes other than T1/T2 is less likely to be associated with mesial temporal onset, but its lateralizing value is similar to that of unilateral scalp onset at T1/T2. The presence of clinical manifestations preceding scalp onset does not reduce the localizing or lateralizing values of scalp recordings.     

Clinical implications of scalp ictal EEG pattern in patients with temporal lobe epilepsy

ObjectiveTo determine the clinical implications of scalp ictal EEG pattern in patients with temporal lobe epilepsy (TLE).MethodsScalp EEG ictal patterns were retrospectively determined in 27 consecutive patients with medically refractory temporal lobe epilepsy who underwent phase-1 scalp video-EEG and phase-2 simultaneous scalp and intracranial video-EEG recordings for pre-surgical evaluation.ResultsOf the 192 temporal lobe seizures recorded during phase-1 and phase-2 scalp video-EEG studies, 124 (65%) seizures were associated with theta/alpha (5–9 Hz) ictal onset pattern, and 68 (35%) seizures were associated with delta (2–5 Hz) ictal onset pattern. Fourteen (52%) patients had exclusively theta/alpha ictal onset, 3 (11%) patients had exclusively delta ictal onset, and 10 (37%) patients had mixed theta/alpha and delta ictal onsets. MTLE was observed in 26 patients who had 124 seizures with theta/alpha ictal onset and 59 seizures with delta ictal onset. LTLE was observed in one patient who had 9 seizures with delta ictal onset. Scalp ictal EEG pattern was not significantly correlated with postsurgical seizure outcomes.ConclusionsBoth scalp delta and theta/alpha ictal onset patterns can be commonly found in patients with MTLE.SignificanceScalp delta ictal onset is not a unique EEG pattern for LTLE as commonly believed.     

Sensitivity of recordings at sphenoidal electrode site for detecting seizure onset: evidence from scalp, superficial and deep foramen ovale recordings.

OBJECTIVES: Some authors have recently stressed that the position of the tip of sphenoidal electrodes plays a crucial role in their efficacy in detecting ictal onset. An opportunity to test this hypothesis is provided by recordings from the most superficial contacts of foramen ovale (FO) electrode bundles because these contacts are located at the FO, in a position equivalent to that of optimally located sphenoidal electrodes. To simplify wording, recordings obtained by superficial FO electrodes will hereafter be called sphenoidal recordings, although they have not been obtained with standard sphenoidal electrodes. The sensitivities of simultaneous scalp and sphenoidal recordings for detecting ictal onset have been compared with each other, and with a 'gold standard' provided by simultaneous deep intracranial FO recordings from the mesial aspect of the temporal lobe. METHODS: Three hundred and fourteen seizures obtained from 110 patients under telemetric presurgical assessment for temporal lobe epilepsy have been studied. Scalp electrodes included anterior temporal placements. All scalp electrodes were considered when identifying seizure onset but the anterior temporal electrodes were most frequently involved. RESULTS: Ictal onset time at sphenoidal and scalp recordings: initial ictal changes appeared simultaneously in scalp and sphenoidal recordings in 123 seizures (39.2%). Initial changes occurred earlier in sphenoidal recordings in 63 seizures (20.1%), whereas they were seen earlier on the scalp in 76 seizures (24.2%). Artefacts prevented the comparison between sphenoidal and scalp recordings in 16 seizures (5.1%) and no ictal changes were seen on the scalp and/or sphenoidal recordings in 36 seizures (11.5%). In most of the 63 seizures where ictal changes appeared earlier in sphenoidal recordings, a delayed ipsilateral scalp onset was seen as the signal amplitude increased or scalp changes could be identified retrospectively on the scalp with an onset which appeared simultaneous and ipsilateral to the initial sphenoidal changes. Sphenoidal recordings supplied additional information when compared to scalp recordings in only 22 seizures (7%): in 5 seizures with artefacts on the scalp, in 6 seizures with no changes on the scalp and in 11 seizures with discrepant laterality at onset. Congruence in laterality with respect to deep intracraneal FO recordings: of the 61 seizures with unilateral onset on the scalp, onsets at sphenoidal recordings and deep FO electrodes were ipsilateral in most cases. In only 3 of these 61 seizures (4.9%), sphenoidal recordings lateralized ipsilateral to the deep FO electrodes in the presence of a contralateral onset on the scalp. In 14 among the 122 seizures (11.5%) with bilateral asymmetrical onset on the scalp, sphenoidal recordings lateralized seizure onset ipsilateral to the deep FO electrodes in the presence of a contralateral scalp onset. Thus, when compared with scalp EEG, sphenoidal recordings increased laterality congruence with respect to deep FO electrodes in 17 seizures (5.4%). CONCLUSIONS: Extracranial electrodes located next to the FO at the sphenoidal electrode site yield an improvement over suitable surface electrodes in the identification of ictal onset in only 5.4-7% of seizures. Such improvement derives from the fact that the low amplitude signals often seen at seizure onset may show higher amplitude on sphenoidal than on scalp recordings.     

Unilateral hippocampal sclerosis with contralateral temporal scalp ictal onset

PURPOSE: To investigate the clinical characteristics and surgical outcomes in patients with unilateral hippocampal sclerosis whose scalp ictal EEG recordings localize to the opposite temporal lobe. METHODS: We retrospectively reviewed the data of all adult patients who had undergone depth electrode implantation for suspected temporal lobe epilepsy (TLE) at UCLA (1993-2000) or the Montreal Neurological Institute (1991-1998) to identify patients who had (a) unilateral hippocampal atrophy, and (b) surface ictal recordings in which the majority of seizures appeared to initiate in the opposite temporal lobe, with few or none that were concordant with the hippocampal atrophy. RESULTS: Of 109 patients with suspected TLE who underwent depth electrode study at the two centers, five patients met the aforementioned criteria. Four of these five had very severe hippocampal atrophy, whereas the fifth had mild atrophy but extensive signal change on magnetic resonance imaging (MRI). Depth electrode recordings in four of the five patients yielded clear ictal onset in the mesial temporal lobe ipsilateral to the imaging abnormality (contralateral to apparent scalp ictal onset). One patient had an unusual bitemporal onset pattern, which was nonetheless suggestive of onset in the sclerotic hippocampus. No patient had intracranial ictal onset contralateral to the imaging abnormality. All patients underwent resection of the structurally abnormal temporal lobe. After follow-up of > or = 2 years, four (80%) of five patients were seizure free, while the fifth showed lesser improvement (class III). CONCLUSIONS: Some patients with severe hippocampal sclerosis (sometimes called a "burned-out hippocampus") have atypical spread of ictal discharges, resulting in apparent gross discordance between imaging and scalp ictal recordings. These patients nonetheless have excellent surgical outcomes on the whole. Whether such patients may forego intracranial recordings requires further study.     

Localization of epileptogenic zone in temporal lobe epilepsy by ictal scalp EEG.

Our aim was to evaluate the ability to localize the epileptogenic zone in temporal lobe epilepsy (TLE) by ictal scalp electroencephalogram (EEG). Using simultaneous video recording, we analysed scalp EEG activity during ictal periods in 38 patients (30 patients with medial TLE (MTLE) and eight with lateral TLE (LTLE)). In 14 patients, intracranial ictal EEGs were recorded with depth electrodes, and simultaneous recordings of scalp and intracranial EEG were performed in 11 patients. Scalp EEG showed that, in all 30 patients with MTLE (71 of 72 seizures), an attenuation of background activity was observed before the appearance of ictal activity. Ictal discharges first appeared in the scalp EEG when the ictal discharges reached the lateral part of the temporal lobe on the intracranial EEG. While, in all eight patients with LTLE (25 of 25 seizures), the attenuation of background activity did not occur before the appearance of ictal activity. When the ictal discharges started in the lateral temporal lobe on intracranial EEG, ictal discharges appeared on the scalp. MTLE and LTLE could be diagnosed by the presence or absence of attenuation of background activity with clinical ictal signs before the appearance of ictal discharges.     

Computer enhancement of scalp-sphenoidal ictal EEG in patients with complex partial seizures

Color topographic maps of scalp/sphenoidal ictal EEG records were computer-generated in 5 patients with medically refractory complex partial seizures of suspected temporal lobe origin. Seven ictal EEG records were analyzed by parsing them into a series of 1.28 sec epochs. User-interactive, computer techniques were utilized to replace eye movement and other artifactual segments in the peri-ictal records with nearby uncontaminated EEG segments. Artifact replacement techniques were designed to minimize or eliminate EEG discontinuities in those epochs in which artifact was removed. Significance probability maps consisting of z scores were constructed by comparing theta band power for each 1.28 sec epoch composing the peri-ictal period with the mean and standard deviation of theta power computed from a pre-ictal baseline period consisting of 50-75 epochs. The resulting maps were compared with available independent clinical measures in order to validate their usefulness. The independent measures consisted of non-invasive data (visual impressions of raw scalp/sphenoidal ictal EEGs and positron emission tomography) and invasive data (depth ictal recordings, pathological findings in resected temporal lobes, and surgical outcome). Ictal topographic maps appeared to either confirm or provide new localizing information in all 5 patients. In 3 of 5 patients, several seconds of localized theta suppression preceded localized theta augmentation during the peri-ictal period. The transition between the 2 states was very rapid (approximately 2 sec). The spatial locus of suppression was always in agreement with the spatial locus of augmentation. In general, the maps were considerably easier to interpret than the raw scalp/sphenoidal ictal EEGs: (1) Localized theta suppression in the maps was not evident from visual inspection of the raw ictal scalp/sphenoidal EEG. (2) Clear localized theta augmentation in the maps occurred well before the appearance of unambiguous phase reversals in the raw scalp/sphenoidal ictal EEG. (3) Mapping data were correctly lateralizing in 1 patient in whom visual interpretation of the raw scalp/sphenoidal ictal EEGs was considered non-localizing but often suggestive of a seizure origin in the hemisphere contralateral to that implicated by depth recordings, PET, and pathological data. These results suggest that topographic mapping of scalp/sphenoidal ictal EEGs in patients with complex partial seizures may eventually prove to be a useful adjunct to the interpretation of raw ictal recordings.     

Palliative temporal resection for the treatment of intractable bioccipital epilepsy.

RATIONALE: Temporal resection is usually ineffective in patients with occipital seizures. However, when seizures are unilateral occipital resections are now, occasionally, considered. When bilateral seizures and visual field defects exist, occipital resection can not be carried out. When predominantly lateralized, temporal seizure onset can be shown in such patients, palliative temporal resection may be justified. METHODS: We report two patients with medically refractory, bilateral occipital lobe seizures. Clinical and electrophysiological patterns suggested consistent spread of the ictal discharge to temporal lobe structures. Long-term EEG video monitoring was followed by stereoelectroencephalography (SEEG) to assess involvement of temporal and occipital regions symmetrically. RESULTS: Both patients had non-lateralized, elementary visual aura followed by loss of contact, automatisms, frequent falls and occasionally secondary generalization. Brain MR imaging revealed bilateral parieto-occipital ischemic lesions without concomitant temporal volumetric abnormalities. They had bilateral or unilateral visual field defects. Scalp EEGs showed bilateral temporal or temporo-parieto-occipital interictal and ictal epileptic abnormalities. Intracranial SEEG recordings confirmed the presence of multifocal, temporo-occipital epileptic abnormalities. In both however, disabling seizures originated in, or rapidly spread to the right hippocampus. Since occipital resections were inadvisable, both patients underwent selective, right amygdalohippocampectomy. Seizures continued in both (two-year follow-up), but were much less severe, not associated with falling or secondary generalization, not followed by fatigue or headache and with faster recovery. CONCLUSION: When occipital resection is inadvisable because of bilateral or diffuse visual problems, palliative temporal resection may be considered in patients with lesional, bilateral occipital lobe epilepsy, and rapid seizure spread to mesial temporal structures. (Published with videosequences).     

Ictal scalp EEG findings in patients with mesial temporal lobe epilepsy.

The syndrome of mesial temporal lobe epilepsy (MTLE) is a well-defined clinical entity that responds to surgical treatment in a considerable number of patients. Although it has been subjected to intensive clinical research, few investigators have published the ictal scalp EEG findings and looked for specific features that might predict postoperative outcome. This study was designed to examine ictal scalp EEG characteristics in detail, in a group of patients with pathologically confirmed hippocampal sclerosis (HS). Patients who underwent long-term video-EEG monitoring at our center during a 3-year period and were diagnosed to have MTLE and pathologically proven HS were included in this retrospective study. All ictal scalp EEGs were investigated in a common reference montage, paying attention to the localization, morphology and frequency of ictal discharges that were accepted to represent a specific phase if the findings were sustained for at least 3 seconds. Any significant change in localization, morphology or frequency of discharges was said to represent a different phase. The ictal EEG patterns in different phases were later compared among seizures of different patients. In addition, the ictal EEG characteristics of the patients in Group I (Engel's classification) were compared with the ictal EEG findings in patients who were included in another group. All the patients have been followed for more than 5 years. Seventy-one ictal EEGs were investigated in 25 adult patients (11 M, 14 F). Onset patterns were lateralized in 81.7% and localized in 76% of the seizures. Thirteen different patterns of onset were detected, the most common of which was the cessation of interictal discharges (35.2%). The most common ictal pattern following the initial changes was ipsilateral temporal rhythmic theta-delta activity (85.2%) that occurred on the average 13.4 seconds after onset. Nonlocalized/lateralized seizure onset of all the seizures or bilateral independent onset was present in 75% of the patients in Groups II-III, whereas this ratio was 14.3% in the patients in Group I (p=0.031). In conclusion, ictal scalp EEG in MTLE allows correct lateralization and localization in most of the seizures. Onset patterns may vary considerably; however, a later significant pattern consisting of rhythmic ipsilateral temporal build-up develops in the majority of seizures. Some ictal EEG characteristics may be related to post-operative outcome.     

Foramen ovale electrodes can identify a focal seizure onset when surface EEG fails in mesial temporal lobe epilepsy

PURPOSE: We analyze a series of patients with mesial temporal lobe epilepsy (MTLE) associated with hippocampal sclerosis (HS) submitted to presurgical investigation with scalp sphenoidal, followed by foramen ovale electrodes (FO), and, when necessary, with depth temporal electrodes. We sought to evaluate the clinical utility of FO in patients with MTLE-HS. METHODS: We included patients who had phase I investigation with bitemporal independent seizures, nonlateralized ictal onsets, or ictal onset initiating in the side contralateral to the side of hippocampal sclerosis. Patients whose implanted FO failed to demonstrate an unambiguous unilateral ictal onset were later evaluated with depth hippocampal electrodes. RESULTS: Between May 1994 and December 2004, 64 patients met our inclusion criteria: 33 female (51.5%) and 31 male subjects (48.5%). The mean age at enrollment was 37.66+/-10.6 years (range, 12-56 years). The groups with nonlateralized surface ictal EEG onsets and contralateral EEG onsets had a greater chance of lateralization with FO when compared with the group with bilateral independent seizures on surface EEG (p<0.01). Foramen ovale electrodes lateralized the seizures in 60% of patients. Seventy percent of patients became seizure free after temporal lobectomy. Five patients were implanted with depth temporal electrodes after FO video-EEG monitoring. The depth-electrode EEG onsets confirmed the results of FO video-EEG monitoring in all patients, and the surgery was refused. CONCLUSIONS: In MTLE-HS, FO is a reliable method for lateralization of seizures that are not clearly recorded by surface EEGs.     

Scalp EEG in temporal lobe epilepsy surgery

Electroencephalography (EEG) with standard scalp and additional noninvasive electrodes plays a major role in the selection of patients for temporal lobe epilepsy surgery. Recent studies have provided data supporting the value of interictal and postictal EEG in assessing the site of ictal onset. Scalp ictal rhythms are morphologically complex but at least one pattern (a five cycles/second rhythm maximum at the sphenoidal or anterior temporal electrode) occurs in >50% of patients and has a high predictive value and interobserver reliability for temporal lobe originating seizures. Thorough interictal and ictal scalp EEG evaluation, in conjunction with modern neuroimaging, is sufficient for proceeding to surgery without invasive recordings in some patients. Further studies are required to define the scalp ictal characteristics of mesial vs. lateral temporal lobe epilepsy.     

Reliability and accuracy of localization by scalp ictal EEG

One hundred forty-four scalp ictal EEGs from 54 patients were analyzed independently by three electroencephalographers for side and lobe of seizure onset. Observers did not know the patients' identities. Accuracy was determined by depth EEG. We found 58 to 60% agreement between observers for lobe, and 64 to 74% for side, of seizure onset; 21 to 38% agreement with depth EEG for lobe, and 46 to 49% agreement for side, of seizure onset; best accuracy for lateralization of seizure onset in temporal lobe seizures, but erroneous in 3 to 17%. More formal criteria are needed before scalp ictal records can be used reliably or accurately for localization.     

Intracranial EEG Substrates of Scalp Ictal Patterns from Temporal Lobe Foci

Summary: Purpose: To determine the intracranial EEG features responsible for producing the various ictal scalp rhythms, which we previously identified in a new EEG classification for temporal lobe seizures. Methods: In 24 patients, we analyzed simultaneous intracranial and surface ictal EEG recordings (64 total channels) obtained from a combination of intracerebral depth, subd-ural strip, and scalp electrodes. Results: Four of four patients with Type 1 scalp seizure patterns had mesial temporal seizure onsets. However, discharges confined to the hippocampus produced no scalp EEG rhythms. The regular 5- to 9-Hz subtemporal and temporal EEG pattern of Type 1a seizures required the synchronous recruitment of adjacent inferolateral temporal neocortex. Seizure discharges confined to the mesiobasal temporal cortex produced a vertex dominant rhythm (Type 1c) due to the net vertical orientation of dipolar sources located there. Ten of 13 patients with Type 2 seizures had inferolateral or lateral, temporal neocortical seizure onsets. Initial cerebral ictal activity was typically a focal or regional, low voltage, fast rhythm (20–40 Hz) that was often associated with widespread background flattening. Only an attenuation of normal rhythms was reflected in scalp electrodes. Irregular 2- to 4-Hz cortical ictal rhythms that commonly followed resulted in a comparably slow and irregular scalp EEG pattern (Type 2a). Type 2C seizures showed regional, periodic, 1– to 4-Hz sharp waves following intracranial seizure onset. Seven patients had Type 3 scalp seizures, which were characterized by diffuse slowing or attenuation of background scalp EEG activity. This resulted when seizure activity was confined to the hippocampus, when there was rapid seizure propagation to the contralateral temporal lobe, or when cortical ictal activity failed to achieve widespread synchrony. Conclusions: Type 1, 2, and 3 scalp EEG patterns of temporal lobe seizures are not a reflection of cortical activity at seizure onset. Differences in the subsequent development, propagation, and synchrony of cortical ictal discharges produce the characteristic scalp EEG rhythms.     

Bilateral mesial temporal lobe epilepsy: comparison of scalp EEG and hippocampal MRI-T2 relaxometry

OBJECTIVE: Bilateral hippocampal abnormality is frequent in mesial temporal lobe sclerosis and might affect outcome in epilepsy surgery. The objective of this study was to compare the lateralization of interictal and ictal scalp EEG with MRI T2 relaxometry. MATERIAL AND METHODS: Forty-nine consecutive patients with intractable mesial temporal lobe epilepsy (MTLE) were studied with scalp EEG/video monitoring and MRI T2 relaxometry. RESULTS: Bilateral prolongation of hippocampal T2 time was significantly associated with following bitemporal scalp EEG changes: (i) in ictal EEG left and right temporal EEG seizure onsets in different seizures, or, after regionalized EEG onset, evolution of an independent ictal EEG over the contralateral temporal lobe (left and right temporal asynchronous frequencies or lateralization switch; P = 0.002); (ii) in interictal EEG both left and right temporal interictal slowing (P = 0.007). Bitemporal T2 changes were not, however, associated with bitemporal interictal epileptiform discharges (IED). Lateralization of bilateral asymmetric or unilateral abnormal T2 findings were associated with initial regionalization of the ictal EEG in all but one patient (P < 0.005), with lateralization of IED in all patients (P < 0.005), and with scalp EEG slowing in 28 (82,4%) of 34 patients (P = 0.007). CONCLUSION: Our data suggest that EEG seizure propagation is more closely related to hippocampal T2 abnormalities than IED. Interictal and ictal scalp EEG, including the recognition of ictal propagation patterns, and MRI T2 relaxometry can help to identify patients with bitemporal damage in MTLE. Further studies are needed to estimate the impact of bilateral EEG and MRI abnormal findings on the surgical outcome.     

Frequency of bitemporal independent interictal epileptiform discharges in temporal lobe epilepsy

PURPOSE: Bitemporal interictal epileptiform discharges (IEDs) occur in < or =42% of scalp EEGs in patients with temporal lobe epilepsy (TLE) studied with routine EEGs or partial analysis of long-term recordings. METHODS: Twenty-eight patients with TLE demonstrating exclusively unilateral temporal IEDs on routine EEGs underwent 24-h continuous recording. The entire record was visually inspected for epileptiform discharges. We used continuous EEG to assess the significance of long-term recording in detecting bilateral IEDs. RESULTS: Twenty-two patients had left temporal IEDs; 21 had right temporal IEDs. Seventeen (61%) patients had IEDs originating from both the right and left temporal lobes. The probability of detecting bilateral independent IEDs was correlated with the duration of continuous EEG recording. There was no correlation between the number of IEDs originating from one side and the probability of detecting independent IEDs on the other side. The frequencies of IEDs were not correlated with the length of time since onset of epilepsy. CONCLUSIONS: The findings suggest that when long-term recordings are performed, the incidence of bilateral discharges in TLE is higher than previously reported in the literature and supports the view that TLE is commonly a bilateral disease.     

Analysis of electrical discharges made with the foramen ovale electrode recording technique in mesial temporal lobe epilepsy patients.

Foramen ovale electrode (FOE) implantation is usually indicated in patients with mesial temporal lobe (MTL) epilepsy. The authors conducted this study to characterize the electrical discharge patterns obtained using FOE recording and evaluated their clinical significance. Interictal and ictal discharge patterns and their temporal relationships to EEGs were examined in 16 patients who had FOEs implanted bilaterally and had good recovery from surgery. After long-term telemetry recording with FOEs, all patients displayed clear seizure onsets originating in one or both sides of the MTL and underwent an anterior temporal lobectomy. Interictal epileptiform discharges (IEDs) were lateralized to the operated side in 12 patients based on scalp EEGs and in 8 patients based on FOE recordings. Among the various possible IED patterns observed with the FOE recordings, a periodic pattern was dominant in the operated side (P = 0.001), whereas a polyspike pattern was dominant in the nonoperated side (P = 0.002). The number of patients with ictal onsets in the operated side was five based on the scalp EEG and 10 based on FOE recordings. Paroxysmal fast frequency activity, rhythmic spikes (>2 Hz), or sharp waves were dominant over other FOE seizure onset patterns in the operated side. By contrast, delta and theta slowing and positive spikes were prevalent in the nonoperated side. The start-stop-start pattern, previously described using subdural electrodes, was also found in FOE recordings and was concordant with the operated side in all cases. The interhemispheric propagation time recorded with bilateral FOEs was 22.6 +/- 20.0 seconds for ictal discharges initiated in the operated side and 7.0 +/- 8.4 seconds for those in the nonoperated side. Among various IED spreading patterns, the most prevalent progression was FOE --> contralateral FOE --> ipsilateral temporal lobe, or --> contralateral temporal lobe. In this series, FOE implantation caused no serious complications. FOE recording appears to be useful for confirming lateralization in patients with MTL epilepsy previously determined using clinical and neuroimaging methods. A thorough analysis of FOE recordings can provide information that may facilitate the differentiation of primary from secondary (nonepileptogenic) temporal lobes.     

False lateralization by surface EEG of seizure onset in patients with temporal lobe epilepsy and gross focal cerebral lesions

Medically intractable temporal lobe seizures developed in 3 patients with radiological and clinical evidence of a gross focal cerebral lesion acquired early in life. All had bilateral independent epileptogenic discharges from the lateral and inferomesial regions of both hemispheres. Scalp and sphenoidal electroencephalographic (EEG) recordings suggested that the seizures originated from the side contralateral to the known cerebral lesion. Because the lateralizing evidence presented by the ictal EEG conflicted with the clinical data, depth electrodes were implanted stereotaxically to determine the side of onset of the seizures. These studies showed that the seizures originated from the limbic structures of the damaged hemisphere in all 3 patients. At operation the mesial temporal lobe structures showed gliotic changes in all. The patients have remained seizure-free for 3 to 13 years postoperatively. These findings suggest that depth electrode recordings may be required to clarify the lateralization of seizure onset in such cases. Extracranial EEG findings must be interpreted with caution in epileptic patients who have gross focal lesions.     

Interictal EEG and ictal scalp EEG propagation are highly predictive of surgical outcome in mesial temporal lobe epilepsy

PURPOSE: Surgical outcome in patients with mesial temporal lobe sclerosis (MTS) is worse than that in patients with temporal lobe activity (TLE) with tumors. Previous studies of the ictal EEG focused on ictal EEG onset in scalp EEG or ictal EEG propagation in invasive recordings. Ictal EEG propagation with scalp electrodes has not been reported. METHODS: Ictal scalp EEG propagation patterns were studied in 347 seizures of 58 patients with MTS or nonlesional TLE. Interictal epileptiform discharges (IEDs) and the presence of unilateral mesial temporal lobe atrophy in magnetic resonance imaging (MRI) also were studied in these 58 patients. Forty-nine patients were operated on (minimal follow-up of 1 year). RESULTS: Postoperatively, seizure-free outcome was seen in (a) 82.8% of patients with regionalized EEG seizure without contralateral propagation, but in only 45.5% of patients with contralateral propagation (p = 0.007); (b) 84.6% of patients with 100% IED lateralized to one temporal lobe, but in only 52.2% with <100% unitemporal IED (p = 0.015); (c) 88.9% with 100% unitemporal IED and regionalized ictal EEG combined, 73.7% with one of both variables, and only 33.3% with <100% ipsitemporal IED combined with contralateral ictal EEG propagation (p = 0.007). CONCLUSIONS: Switch of lateralization or bitemporal asynchrony in the ictal scalp EEG and bitemporal IED are most probably an index of bitemporal epileptogenicity in MTS and are associated with a worse outcome.     

Interictal, unifocal spikes in refractory extratemporal epilepsy predict ictal origin and postsurgical outcome.

OBJECTIVES: To evaluate the significance of exclusively unifocal, unilateral, interictal epileptiform patterns on scalp electroencephalography (EEG) in surgical candidates with medically intractable extratemporal epilepsy. METHODS: We reviewed 126 patients with refractory extratemporal partial seizures who underwent epilepsy surgery at our center. All were followed for at least 2 years after resections. Surgery was based on ictal EEG recordings. We examined ictal onsets and surgical outcome in subjects whose preoperative, interictal scalp EEGs during long-term monitoring (LTM) demonstrated only unilateral, well-defined focal discharges, and outcome in patients whose interictal EEGs during LTM showed bilateral, non-localized, or multifocal epileptiform patterns. RESULTS: We found that 26 subjects exhibited only unilateral, unifocal, interictal epileptiform patterns. In all 26 cases (100%) clinical seizures arose from the regions expected by the interictal findings (P<0.0001, Sign test). At last follow-up 77% (20/26) of these patients were seizure-free, while 23% (6/26) had >75% reduction in seizures. This compares to the remaining patients, of whom 34% (34/100) were seizure-free, 41% (41/100) had >75% reduction in seizures, and 25% (25/100) had <75% reduction in seizures (P=0.0001, Fisher's Exact test). CONCLUSIONS: Strictly unifocal, interictal epileptiform patterns on scalp EEG, though seen in a minority of subjects, may be an important, independent factor in evaluating subjects with intractable extratemporal, localization-related epilepsy for surgical therapy. This finding is highly predictive of both ictal onsets and successful postsurgical outcome.     

Ictal spikes: a marker of specific hippocampal cell loss.

Spontaneous seizures recorded from mesial temporal depth electrodes in the human are commonly manifested by one of two onset patterns: a high frequency discharge or a periodic spike discharge morphologically similar but clearly distinguished from ongoing interictal activity. We categorized medial temporal lobe seizure onset for the presence of periodic ictal spikes at a frequency of less than 2 Hz lasting for more than 5 sec to investigate the relationship of this ictal pattern to anatomical changes in the resected temporal lobe tissue. Fifty-one patients had hippocampal depth electrode recordings of spontaneous seizures, subsequent hippocampal resection, and quantitative cell counts of hippocampal subfields. Thirty-two of these patients had ictal spikes lasting at least 5 sec in more than 50% of their seizures. The presence of ictal spikes was significantly correlated with decreased cells in CA1 only (P = 0.015). The correlation of a common ictal pattern with focal cell loss in the hippocampus suggests that electrophysiological manifestations of seizures provide a clue to the underlying pathological substrate. Ictal spikes may be a cause or result of the cell loss. These observations should be correlated with independent investigations in humans and animal models that reflect the CA1 cell loss associated with temporal lobe epilepsy.