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.     

Is ictal recording mandatory in temporal lobe epilepsy? Not when the interictal electroencephalogram and hippocampal atrophy coincide

OBJECTIVE: To investigate the concordance between scalp electroencephalogram (EEG) lateralization and side of hippocampal atrophy in patients with temporal lobe epilepsy (TLE). METHODS: We studied 184 consecutive patients with TLE without lesions other than those compatible with mesial temporal sclerosis. In this study, we studied specifically hippocampal atrophy and the results of scalp EEG investigation. Patients were classified according to the localization of interictal epileptiform discharges as unilateral, bilateral asymmetric, and bilateral symmetric. The EEG seizure onsets were also classified separately as unilateral, bilateral asymmetric, and bilateral symmetric. The hippocampal atrophy was determined by volumetric measurements using high-resolution magnetic resonance imaging (MRIVol). RESULTS: Only 3% of patients had discordance between the ictal and interictal EEG lateralizations; however, none of these had unilateral interictal EEG abnormalities. Interictal EEGs were considered unilateral in 62.0% of patients, bilateral asymmetric in 31.5%, and bilateral symmetric in 6.5%. Ictal EEGs were considered unilateral in 63.5% of patients, bilateral asymmetric in 30.0%, and bilateral symmetric in 6.5%. The MRIVol showed unilateral hippocampal atrophy in 60.9% of patients, bilateral asymmetric hippocampal atrophy in 19.0%, symmetric hippocampal atrophy in 3.8%, and normal volumes in 16.3%. There was a significant concordance between MRIVol lateralization and both interictal and ictal EEG lateralization (P<.001). All patients with unilateral hippocampal atrophy had concordant interictal and ictal EEG lateralization. Six (18.2%) of the 33 patients with bilateral asymmetric hippocampal atrophy had MRI lateralization discordant with EEG lateralization. CONCLUSIONS: We found a strong concordance between EEG and MRIVol lateralization in patients with TLE. Unilateral hippocampal atrophy predicted ipsilateral interictal epileptiform abnormalities and ipsilateral seizure onsets with no false lateralization. Previous studies in addition to the present series support that a concordant outpatient EEG evaluation in patients with TLE and unilateral hippocampal atrophy would obviate the need for inpatient EEG monitoring.     

无创性定位手段在颞叶内侧癫(癎)患者癫(癎)灶定位中的价值

目的 评价多种无创性定位手段在颞叶内侧癫(癎)患者术前癫(癎)灶定位中的可靠性.方法 选择2002年5月至2005年5月间在我院行前颞叶内侧切除,随访1年以上,预后为Engle I级的40例患者,回顾性地总结这组病例发作间期和发作期脑电图、发作症状、头颅MRI、发作问期SPECT所提供的定侧定位信息,分析其在癫疴灶定位中的价值.结果 (1)发作间期颞前尖波:出现单侧独立尖波者37例(92.5%),其中35例(94.6%)与癫(癎)灶侧别相符;(2)发作期脑电图:32例获取了发作期脑电图,26例(81.2%)的发作期脑电图可提供定侧信息,其中25例(96.2%)与癫(癎)灶的侧别相符;(3)发作症状:23例(57.5%)患者的发作症状可以提供癫(癎)灶侧别信息,其中19例(82.6%)提供的侧别信息与癫(癎)灶侧别一致;(4)头颅MRI:38例(95.0%)头颅MRI提示一侧海马及颞叶的信号或结构异常,其中37例(97.4%)与癫(癎)灶侧别相符;(5)发作间期SPECT:23例患者行同位素检查,22例(95.7%)可提供癫(癎)灶侧别信息,其中18例(81.8%)与癫(癎)灶侧别相符.结论 颞叶内侧癫(癎)术前无创性定位定侧方法中,提供定侧信息比较敏感的方法依次为SPECT、MRI、发作问期脑电图、发作期脑电图和发作症状,而定侧信息可靠性的高低依次为头颅MRI、发作期脑电图、发作间期脑电图、发作症状和SPECT.     

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.     

Accuracy of ictal SPECT in mesial temporal lobe epilepsy with bilateral interictal spikes

OBJECTIVE: In mesial temporal lobe epilepsy (MTLE), the rate of correct seizure lateralization of ictal semiology and ictal EEG is better for patients with unilateral interictal spikes (UIS) than for patients with bilateral interictal spikes (BIS), possibly due to rapid seizure propagation patterns associated with bilateral epileptogenesis. In this study, the authors investigated if ictal SPECT is a reliable diagnostic test for both UIS and BIS patients. METHODS: Video-EEG recording was used as the gold standard to examine the accuracy of ictal SPECT and its relationship with interictal and ictal EEG. Ninety-three consecutive patients with MTLE associated with hippocampal sclerosis were included in the analysis. Ictal SPECT was considered accurate if two blinded observers independently lateralized the scan correctly. RESULTS: Ictal SPECT correctly lateralized 75 (80.6%) of 93 scans. The rate of correct seizure lateralization was 87.6% for the UIS group and only 55.0% for the BIS group (p = 0.0027). In the EEG epochs, 66.7% of BIS patients vs 43.4% of UIS patients had nonlateralized ictal EEG (p < 0.001). CONCLUSION: The authors conclude that the accuracy of ictal SPECT is worse for MTLE patients with BIS than for those with UIS. The role of ictal SPECT in presurgical evaluation of patients with BIS must be reviewed.     

Lack of aura experience correlates with bitemporal dysfunction in mesial temporal lobe epilepsy

The diagnostic value of lack of aura experience in patients with temporal lobe epilepsy (TLE) is unclear. PURPOSE: To evaluate possible factors of bitemporal dysfunction in patients with mesial TLE who did not experience an aura in electroencephalography EEG/video monitoring for epilepsy surgery. METHODS: Ictal scalp EEG propagation patterns of 347 seizures of 58 patients with mesial temporal lobe sclerosis or non-lesional mesial TLE, interictal epileptiform discharges (IED), presence of unilateral mesial temporal lobe sclerosis in visual magnetic resonance imaging (MRI) analysis, prose memory performance, history or not of an aura, and postictal memory or absence of an aura were analyzed. The ictal EEG was categorized as follows. EEG seizure: (a) remaining regionalized, (b) non-lateralized, (c) showing later switch of lateralization or bitemporal asynchronous ictal patterns. RESULTS: Absent aura in monitoring was significantly correlated with absence of unitemporal MRI sclerosis (P=0.004), bitemporal IED (P=0.008), and propagation of the ictal EEG to the contralateral temporal lobe (P=0.001). Other historical data and interictal prose memory performance were not significantly correlated with absent aura. Ten of 11 patients without aura in monitoring also had absent or rare auras in their history. CONCLUSIONS: Lack of aura experience strongly correlates with indicators of bitemporal dysfunction such as bitemporal interictal sharp waves and bitemporal ictal propagation in scalp EEG, and absence of lateralized MRI sclerosis in patients with mesial TLE. The fact that absent auras are not correlated with episodic memory suggests a transient memory deficit, probably because of rapid propagation to the contralateral mesial temporal lobe.     

Spatiotemporal relationship between seizure activity and interictal spikes in temporal lobe epilepsy.

PURPOSE: To analyze the spatio-temporal relationship between seizure propagation and interictal epileptiform discharges (IEDs) in patients with bitemporal epilepsy. METHODS: We investigated 18 adult patients with intractable temporal lobe epilepsy (TLE) who had undergone continuous video-EEG monitoring during presurgical evaluation. Only those patients were selected who had independent IEDs over both temporal lobes. Two authors evaluated the ictal and interictal EEG data independently. RESULTS: We analyzed 52 lateralized seizures of 18 patients. Thirty-one seizures showed ipsilateral seizure spread exclusively, whereas in 21 seizures the contralateral hemisphere was also involved. In lateralized seizures without contralateral propagation, we found that spikes ipsilateral to the seizure onset occurred postictally in a greater ratio than preictally (P<0.001). In lateralized seizures with contralateral propagation, we found no significant changes in the postictal spike distribution. CONCLUSIONS: Our findings showed that the lateralization of IEDs may depend on the brain areas involved by the preceding seizures, suggesting that spikes can be influenced by the seizure activity, and are not independent signs of epileptogenicity.     

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.     

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.     

Factors contributing to clinical seizure lateralization in patients with mesial temporal lobe epilepsy

Clinical seizure semiology can provide important information on the lateralization of the epileptogenic zone. We investigated factors associated with clinical seizure lateralization in patients with pathologically proven mesial temporal sclerosis. We reviewed 243 seizures of 58 patients. Clinical lateralization was possible in 155 (63.8%) of 243 seizures. Lateralization was correct in 144 (92.9%) of 155 lateralized seizures. Logistic regression analysis showed that age at onset (p = 0.001; odds ra tio = 1.089, 95% confidence interval = 1.035-1.145) and the contralateral propagation pattern of ictal discharges (p = 0.001; odds ratio = 3.544, 95% confidence interval = 1.723-7.289) correlated with clinical seizure lateralization. The patient group with clinically lateralized seizures had a younger age at onset of habitual seizures compared to the clinically nonlateralized group (11.1 +/- 6.3 vs. 15.6 +/- 8.4 years; p < 0.001). Of seizures without bitemporal asynchrony or switch of lateralization, 70.7% were clinically lateralized compared with only 46.4% of seizures with asynchrony or lateralization switch. The present results suggest that the age of epilepsy onset and the ictal scalp EEG propagation pattern affect clinical seizure lateralization in patients with mesial temporal sclerosis.     

Dipole Modeling in Epilepsy Surgery Candidates

Summary: Purpose : The validity and clinical significance of dipole modeling in epilepsy surgery candidates is not fully established.
Patients and Methods : Interictal and ictal dipole modeling was performed in 43 patients with refractory complex partial seizures (CPS) and intracranial structural abnormalities demonstrated with optimum magnetic resonance imaging (MRI: space–occupying, n = 15; atrophic, n = 26; dysplastic, n = 2). Video–EEG monitoring showed CPS in all patients. In 12 patients, additional intracranial EEG monitoring demonstrated hippocampal seizure onset in 11 patients and medial occipital ictal onset in 1.
Results : Spatiotemporal dipole mapping of averaged interictal spikes and epochs of early ictal discharges revealed two distinct dipole patterns. Patients with lesions located in the medial (± lateral) temporal lobe (n = 34) and medial occipital lobe (n = 1) uniformly presented a combined interictal dipole that consisted of a radial and a tangential component with a high degree of elevation relative to the axial plane. Eight of 9 patients with extratemporal lesions had a less stable dipole with a predominant radial component. Ictal dipole modeling identified the ictal onset zone correctly as compared with intracranial EEG recordings from bilateral hippocampal depth electrodes. Ictal dipoles showed a striking correspondence with the interictal dipoles in individual patients.
Conclusions : Interictal and ictal dipole mapping provided additional, reliable, and relevant localizing information in surgical candidates for refractory CPS. Ictal dipole analysis may limit the number of patients who require intracranial electrodes.     

Video-EEG monitoring in patients with hippocampal atrophy

OBJECTIVES: To analyze the value of ictal EEG recordings in patients with unilateral magnetic resonance imaging (MRI)-identified hippocampal atrophy and concordant interictal epileptiform discharges (IEDs). MATERIAL AND METHODS: The ictal EEG patterns in 84 patients with pharmaco resistant epilepsy undergoing an anterior temporal lobectomy between 1992 and 1995 were reviewed. The concordance between the ictal EEG and MRI and the IEDs was examined. RESULTS: Two-hundred-and-thirty seizures (76.4%) were concordant and 11 seizures (3.7%) were discordant with the atrophic temporal lobe. Sixty seizures (19.9%) were indeterminate in localization. Sixty-three of the 69 patients (91.3%) with confirmatory and 14 of the 15 patients (93%) with non-confirmatory ictal EEG recordings, respectively, experienced an excellent operative outcome (P=0.629, Fisher's exact test). CONCLUSIONS: Patients with unilateral hippocampal atrophy and concordant IEDs are excellent surgical candidates even when video-EEG monitoring shows discordant or non-localizing seizures.     

The impact of cerebral source area and synchrony on recording scalp electroencephalography ictal patterns

PURPOSE: To determine the cerebral electroencephalography (EEG) substrates of scalp EEG seizure patterns, such as source area and synchrony, and in so doing assess the limitations of scalp seizure recording in the localization of seizure onset zones in patients with temporal lobe epilepsy. METHODS: We recorded simultaneously 26 channels of scalp EEG with subtemporal supplementary electrodes and 46-98 channels of intracranial EEG in presurgical candidates with temporal lobe epilepsy. We correlated intracranial EEG source area and synchrony at seizure onset with the corresponding scalp EEG. Eighty-six simultaneous intracranial- and scalp-recorded seizures from 23 patients were evaluated. RESULTS: Thirty-four intracranial ictal discharges (40%) from 9 patients (39%) had sufficient cortical source area (namely > 10 cm(2)) and synchrony at seizure onset to produce a simultaneous or nearly simultaneous focal scalp EEG ictal pattern. Forty-one intracranial ictal discharges (48%) from 10 patients (43%) gradually achieved the necessary source area and synchrony over several seconds to generate a scalp EEG ictal pattern. These scalp rhythms were lateralized, but not localizable as to seizure origin. Eleven intracranial ictal discharges (13%) from 4 patients (17%) recruited the necessary source area, but lacked sufficient synchrony to result in a clearly localized or lateralized scalp ictal pattern. CONCLUSIONS: Sufficient source area and synchrony are mandatory cerebral EEG requirements for generating scalp-recordable ictal EEG patterns. The dynamic interaction of cortical source area and synchrony at the onset and during a seizure is a primary reason for heterogeneous scalp ictal EEG patterns.     

Outcome after hemispherectomy in hemiplegic adult patients with refractory epilepsy associated with early middle cerebral artery infarcts

Purpose:   To study the outcome after hemispherectomy (HP) in a homogeneous adult patient population with refractory hemispheric epilepsy.
Methods:   Fourteen adult patients submitted to HP were studied. Patients had to be at least 18 years old, and have refractory epilepsy, clearly focal lateralized seizures and unilateral porencephalus consistent with early middle cerebral artery infarct on magnetic resonance imaging (MRI). All patients were submitted to functional hemispherectomy. We analyzed age of seizure onset, age by the time of surgery, gender, seizure type and frequency, interictal and ictal electroencephalography (EEG) findings, MRI and IQ scores preoperatively; seizure frequency, drug regimen, and IQ outcome were studied postoperatively.
Results:   Mean follow-up was 64 months. All patients had frequent daily seizures preoperatively. All patients had unilateral simple partial motor seizures (SPS); 11 patients had secondarily generalized tonic–clonic (GTC) seizures and five patients had complex partial seizures (CPS), preoperatively. All patients had hemiplegia and hemianopsia. Twelve patients had unilateral EEG findings, and in two epileptic discharges were seen exclusively over the apparently normal hemisphere. Twelve patients were seizure-free after surgery and two patients had at least 90% improvement in seizure frequency. Pre- and postoperative mean general IQ was 84 and 88, respectively. Five of the twelve Engel I patients were receiving no drugs at last follow-up. There was no mortality or major morbidity.
Conclusions:   Our results suggest that well-selected adult patients might also get good results after HP. Although good results were obtained in our adult series, the same procedure yielded a much more striking result if performed earlier in life.     

Focal ictal beta discharge on scalp EEG predicts excellent outcome of frontal lobe epilepsy surgery

PURPOSE: To determine whether a focal beta-frequency discharge at seizure onset on scalp EEG predicts outcome of frontal lobe epilepsy (FLE) surgery. METHODS: We identified 54 consecutive patients with intractable FLE who underwent epilepsy surgery between December 1987 and December 1996. A blind review of EEGs and magnetic resonance images (MRIs) was performed. Lesional epilepsy is defined as presence of an underlying structural abnormality on MRI. RESULTS: Overall, 28 (52%) patients were seizure free, with a mean follow-up of 46.5 months. Presence of a focal beta-frequency discharge at seizure onset on scalp EEG predicted seizure-free outcome in lesional (p = 0.02) and non-lesional (p = 0.01) epilepsy patients. At least 90% of patients who had either lesional or non-lesional epilepsy were seizure free if scalp EEG revealed a focal beta discharge at ictal onset. Moreover, logistic regression analysis showed that focal ictal beta pattern and completeness of lesion resection were independently predictive of seizure-free outcome. Ictal onset with lateralized EEG activity of any kind and postresection electrocorticographic spikes did not predict surgical outcome (p > 0.05). CONCLUSIONS: Only about 25% of FLE surgical patients have a focal beta-frequency discharge at seizure onset on scalp EEG. However, its presence is highly predictive of excellent postsurgical seizure control in either lesional or non-lesional FLE surgical patients.     

Drug‐resistant parietal lobe epilepsy: clinical manifestations and surgery outcome

Aim. We reviewed a large surgical cohort to investigate the clinical manifestations, EEG and neuroimaging findings, and postoperative seizure outcome in patients with drug‐resistant parietal lobe epilepsy (PLE). Methods. All drug‐resistant PLE patients, who were investigated for epilepsy surgery at Jefferson Comprehensive Epilepsy Center between 1986 and 2015, were identified. Demographic data, seizure data, EEG recordings, brain MRI, pathological findings, and postsurgical seizure outcome were reviewed. Results. In total, 18 patients (11 males and seven females) were identified. Sixteen patients (88%) had tonic‐clonic seizures, 12 (66%) had focal seizures with impaired awareness, and 13 (72%) described auras. Among 15 patients who had brain MRI, 14 patients (93%) had parietal lobe lesions. Only three of 15 patients (20%) who had interictal scalp EEG recordings showed parietal interictal spikes. Of 12 patients with available ictal surface EEG recordings, only three patients (25%) had parietal ictal EEG onset. After a mean follow‐up duration of 8.6 years, 14 patients (77.7%) showed a favourable postoperative seizure outcome. Conclusion. In patients with PLE, semiology and EEG may be misleading and brain MRI is the most valuable tool to localize the epileptogenic zone. Postsurgical seizure outcome was favourable in our patients with drug‐resistant parietal lobe epilepsy.     

Localizing value of scalp EEG spikes: a simultaneous scalp and intracranial study.

OBJECTIVE: To determine the relationship between cortical origins of interictal and ictal EEG discharges in patients with temporal lobe epilepsy. METHODS: Simultaneous cortical and scalp EEG recordings were obtained from six patients with temporal lobe epilepsy. Subdural electrode contacts active at seizure onset and when scalp ictal rhythms became evident were identified. Similarly, cortical substrates of scalp EEG spikes were identified at spike peak and at the initial rising phase of the potential. RESULTS: Intracranial seizure onsets were commonly focal and involved only a few electrode contacts, as opposed to scalp ictal rhythms, which required synchronous activation of multiple electrode contacts. At the peak of scalp spikes, multiple electrode contacts were similarly active. However, at spike onset, cortical substrates were more discrete and commonly involved electrodes similar to that of seizure onsets. CONCLUSIONS: Scalp EEG ictal rhythms and the peak of a scalp spike may poorly localize the epileptogenic focus because of propagation. Cortical source area at scalp spike onset is more discrete, however, and the seizure onset zone often lies within this area. SIGNIFICANCE: Analysis of scalp spikes, such as source modeling, at their initial rising phase might provide useful localizing information about seizure origins in the same patient.     

Unitemporal vs bitemporal hypometabolism in mesial temporal lobe epilepsy

BACKGROUND: Patients with mesial temporal lobe epilepsy (TLE) often show bilateral temporal hypometabolism (BTH), but the nature of this finding has not been well established. OBJECTIVE: To compare the clinical characteristics between unitemporal hypometabolism (UTH) and BTH patients in mesial TLE. DESIGN: Cross-sectional study. SETTING: Epilepsy center at university hospital in Seoul, Korea. PATIENTS: We enrolled 95 patients with mesial TLE, 87 of whom had subsequently undergone surgery. Seizures, interictal and ictal electroencephalography (EEG), brain magnetic resonance imaging, Wada test, and neuropsychological test results were reviewed. (18)F-fluorodeoxyglucose positron emission tomography scans were interpreted visually. Patients were divided into 2 groups: UTH and BTH. RESULTS: There were 59 UTH patients and 36 BTH patients. Semiologic analysis showed that UTH patients had higher frequencies of aura and unilateral dystonic posturing, whereas BTH patients had higher frequencies of a nonlateralized bilateral ictal EEG pattern and bilateral interictal spikes. Moreover, BTH patients had more frequent symmetric Wada memory scores and white matter changes in the bilateral temporal lobes on brain magnetic resonance imaging than UTH patients. All UTH patients with bilateral TLE on scalp EEG showed unilateral seizure onset on intracranial EEG. CONCLUSIONS: The characteristic clinical findings of mesial TLE with BTH were a more frequent nonlateralized ictal EEG pattern, bitemporal interictal spikes, symmetric Wada memory score, and the anterior temporal white matter changes, and less frequent aura and unilateral dystonic posturing. Surgical outcomes were similar and good in both groups, although surgery could not be performed in 8 BTH patients (22%).     

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.     

False lateralization of scalp EEG seizure onset

We report a patient with lateralized right-sided ictal scalp EEG activity contralateral to left mesial temporal seizure onset as documented by depth electrodes. Subsequent left temporal lobectomy revealed mesial temporal sclerosis and resulted in a marked reduction (97%) in seizure frequency. This case illustrates the frequently discussed, but rarely documented, occurrence of false lateralization of scalp EEG seizure onset in a patient with temporal lobe epilepsy.