Intracranial EEG in temporal lobe epilepsy: location of seizure onset relates to degree of hippocampal pathology

PURPOSE: To determine whether the specific location of electrographic seizure onset in the temporal lobe is related to hippocampal pathology in temporal lobe epilepsy (TLE). METHODS: Consecutive presurgical patients with scalp EEG-video evidence of TLE and no or mild hippocampal atrophy (HA) on magnetic resonance imaging (MRI) were prospectively studied by using depth and subdural strip electrode recordings to identify the site of the initial ictal discharge (IID). Thirty-four patients had either no or mild HA (HA- group). Four additional patients with moderate or marked HA (HA+ group) who required depth and strip electrodes served as a comparison group. Hippocampal pathology was assessed by MRI volumetrics and histopathologic grade of sclerosis (HS). RESULTS: Thirty-eight patients were investigated. In the HA- group, 10 patients had lobar ictal EEG onsets in the hippocampus (HF), medial paleocortex (MPC), and lateral neocortex (LNC); eight cases had regional IIDs in both HF and MPC; 12 persons had IIDs completely outside the HF; three cases lacked depth electrodes, and only one case (3%) had an IID confined to the HF. By contrast, three (75%) of four HA+ cases had IIDs confined to the HF (p = 0.002). Similarly, in 12 patients with low-grade HS, IIDs confined to the HF area were seen significantly less often than in six cases with high-grade HS (p = 0.025). CONCLUSIONS: In this study of a large number of patients with no to mild and a smaller group with moderate to marked HA and HS, the location of seizure onset in the temporal lobe was related to the degree of hippocampal pathology. Absence of HA and low-grade HS was each associated with IIDs in both the hippocampus and medial (with or without lateral) temporal cortex, or only the MPC or LNC. Marked HA and high-grade HS both were associated with IIDs restricted to the HF.     

颞叶癫痫颅内EEG记录定位与海马病理变化的关系

目的探讨颞叶癫痫颅内EEG记录与颞叶海马病变程度的关系。方法视频EEG证实为颞叶癫痫并经MRI检查的病人序贯进入本研究,采用硬膜下电极及深部电极联合纪录,确定领先发作释放(initialictaldischarge,IID)部位。37例病人中,无或轻度海马萎缩(hippocampalatrophy,HA阴性组)27例,中至中度HA(HA阳性组)者10例。海马病理变化依据MRI检查的海马容积测量及术后组织病理学的海马硬化分级。结果本组HA阴性组27例病人中,9例病人IID广泛出现在海马区、内侧旧皮层及外侧新皮层;3例在海马区及内侧古皮层;14例完全出现在海马区以外的颞叶皮层;仅1例局限于海马区。在HA阳性组中,90%的病人IID局限于海马区(P<0.05),在25例低级别海马硬化(HS)中,IID局限于海马区显著低于12例HS高级别病人(P<0.05)。结论颞叶癫痫的抽搐发作放电定位与海马的病理变化存在着密切关系,无HA和低级别HS病人的IID多出现在海马、颞叶内侧皮层、颞叶新皮层的部位,而HA明显者和高级别的HS病人出现的IID往往仅局限于海马(HF)。     

Interictal Epileptiform Discharges in Temporal Lobe Epilepsy Due to Hippocampal Sclerosis Versus Medial Temporal Lobe Tumors

PURPOSE: It remains controversial whether a specific pattern of interictal epileptiform activity exists that may help to differentiate temporal lobe epilepsy (TLE) due to hippocampal sclerosis (HS) from other forms of TLE. In this study, we characterized the distribution of interictal epileptiform discharges in TLE due to HS as compared with those in patients with tumors restricted to the medial temporal lobe structures. METHODS: The study included 21 adult patients with unilateral HS who remained seizure free (>1 year) after anterior temporal lobectomy with amygdalohippocampectomy. Patients with "dual pathology" were excluded. The comparison group consisted of nine patients with tumors restricted to the amygdala and hippocampus. All patients underwent video-EEG monitoring preoperatively by using 39 scalp electrodes (including the 10-10 system over both temporal regions) and bilateral sphenoidal electrodes. RESULTS: The HS patient group showed a significantly higher percentage of ipsilateral epileptiform discharges maximal at anterior temporal electrodes (median, 97.0%; sphenoidal electrode alone, 88.1%), as compared with the tumor group (median, 72.1%; p<0.001; sphenoidal electrode alone, 24.8%; p<0.001). The HS group had significantly fewer extratemporal spikes/sharp waves (median, 0.0), as compared with the tumor group (10.0%; p<0.001). At least 90% of the interictal discharges were located in the anterior temporal region in 20 (95.2%) of 21 HS patients, but in none of the tumor patients (p<0.001). Bilateral temporal discharges were found in nine (42.9%) of 21 patients with HS and in two (22.2%) of nine tumor patients (p = 0.42). CONCLUSIONS: We conclude that ipsilateral interictal epileptiform discharges outside the anterior temporal region are rare (<10%) in adults with intractable TLE due to unilateral HS. Frequent posterior or extratemporal sharp waves may detract from the certainty of this diagnosis in complicated cases. These restricted epileptiform discharges suggest a smaller irritative zone in HS as compared with medial tumors, or a more organized activity associated with intrinsic hippocampal disease. Bilateral epileptiform discharges were not uncommon in both groups.     

Contralateral temporal hypometabolism on positron emission tomography in temporal lobe epilepsy

Introduction — No detailed case studies report lateralised hypometabolism on positron emission tomography (PET) contralateral to the epileptogenic focus in temporal lobe epilepsy (TLE). Material and methods — We performed ¹⁸F fluorodeoxyglucose (FDG) PET in two intractable TLE patients. Results — One had right temporal interictal spikes on electroencephalography (EEG) and a right medial temporal lobe lesion on magnetic resonance imaging (MRI). FDG-PET showed decreased uptake in the left temporal lobe. Right temporal ictal onset, with bilateral interictal epileptiform activity, occurred on intracranial EEG. He is seizure free after right temporal lobectomy and ganglioglioma resection. The second had right temporal lobe interictal and ictal EEG activity. MRI demonstrated right anteriomedial temporal increased T2 signal. Neuropsychology revealed bilateral cognitive dysfunction. FDG-PET showed left anterior temporal and lateral frontal hypometabolism. He is seizure free after right temporal lobectomy. Conclusion — These findings suggest that regional uptake asymmetry on FDG-PET may be give misleading lateralising information in TLE.     

Value of extent of hippocampal resection in the surgical treatment of temporal lobe epilepsy

OBJECTIVE: Unilateral hippocampal atrophy is indicator of good surgical prognosis in patients with temporal lobe epilepsy (TLE). Some patients however do not become seizure free after surgery. We assessed if the extent of hippocampal and amygdala resection is associated with outcome. METHODS: Thirty patients with TLE with unilateral or clearly asymmetric hippocampal atrophy who underwent surgical treatment were evaluated concerning preoperative clinical variables and interictal EEG abnormalities. Amygdala and hippocampal resection was evaluated by post-operative MRI. We compared seizure free versus non-seizure free patients, and patients with good outcome (Engel's classes I and II) versus patients with poor outcome. RESULTS: There was significant association between the extent of hippocampal resection and the outcome. Pre-operative variables and interictal EEG abnormalities did not show relationship with outcome as documented in previous studies. CONCLUSION: The extent of hippocampal resection is associated with outcome. Incomplete resection of atrophic hippocampus may explain most surgical failures in patients with TLE due to unilateral hippocampal sclerosis.     

Temporal lobe epilepsy: analysis of patients with dual pathology

OBJECTIVES: To determine the frequency and types of dual pathology in patients with temporal lobe epilepsy (TLE) and to analyze the clinical manifestations and surgical outcome. MATERIAL AND METHODS: A total of 240 patients with TLE underwent temporal resections following a comprehensive pre-surgical evaluation. Thirty-seven (15.4%) of these had hippocampal sclerosis (HS) or temporal lobe gliosis in association with another lesion (dual pathology). RESULTS: Eighteen of 37 patients with dual pathology had heterotopia of the temporal lobe, nine had cortical dysplasia, four had cavernous angiomas or arteriovenous malformations, one had a dysembryoplastic neuroepithelial tumor, one had a contusion and four patients had cerebral infarctions in childhood. 68.5% had abnormal head magnetic resonance imagings, 91.3% had abnormal positron emission tomography scans, and 96% had abnormal ictal SPECT. The intracarotid amobarbital procedure (IAP) showed impaired memory of the epileptogenic side in 72% of the patients. Twenty patients had left and 17 had right-sided en bloc temporal resections, including the lesion and mesial temporal structures. Twenty-six (70.2%) became seizure-free, eight (21.6%) had rare seizures, two (5.4%) had worthwhile seizure reduction and one (2.7%) had no improvement (range of follow-up 1-16 years, mean = 7.4 years). CONCLUSIONS: 15.4% had dual pathology. The dual pathology was almost exclusively seen in patients whose lesions were congenital, or occurred early in life, suggesting that the hippocampus is more vulnerable and more readily develops HS in early childhood. Resections, including the lateral and mesial temporal structures led to a favorable outcome with no mortality and little morbidity.     

Seizure outcome after anterior temporal lobectomy and its predictors in patients with apparent temporal lobe epilepsy and normal MRI

PURPOSE: Very little reliable information is available regarding the role of anterior temporal lobectomy (ATL), optimal presurgical evaluation strategy, post-ATL seizure outcome, and the factors that predict the outcome in patients with medically refractory temporal lobe epilepsy (TLE) and normal high-resolution magnetic resonance imaging (MRI). To be cost-effective, epilepsy surgery centers in developing countries will have to select candidates for epilepsy surgery by using the locally available technology and expertise. METHODS: We reviewed the electroclinical and pathological characteristics and seizure outcome of 17 patients who underwent ATL for medically refractory TLE after being selected for ATL based on a noninvasive selection protocol without the aid of positron emission tomography (PET) or single-photon emission computed tomography (SPECT), despite a normal preoperative high-resolution MRI. RESULTS: Seven (41%) patients achieved an excellent seizure outcome; five of them were totally seizure free. An additional five (29%) patients had >75% reduction in seizure frequency. The following pre-ATL factors predicted an excellent outcome: antecedent history of febrile seizures, strictly unilateral anterior temporal interictal epileptiform discharges (IEDs), and concordant type 1 ictal EEG pattern. All the five patients with pathologically verified hippocampal formation neuronal loss were seizure free. The presence of posterior temporal, bilateral temporal, and generalized IEDs portended unfavorable post-ATL seizure outcome. CONCLUSIONS: A subgroup of patients destined to have an excellent post-ATL outcome can be selected from MRI-negative TLE patients by using history and scalp-recorded interictal and ictal EEG data. The attributes of these patients are antecedent history of febrile seizures, strictly unilateral anterior IEDs, and concordant type 1 ictal EEG pattern.     

Postoperative interictal spikes during sleep contralateral to the operated side is associated with unfavourable surgical outcome in patients with preoperative bitemporal spikes.

PURPOSE: To correlate the persistence of contralateral spikes during sleep after unilateral surgery with seizure outcome in a temporal lobe epilepsy (TLE) population and to test the existing hypotheses about the origin of the contralateral spikes in temporal lobe epilepsy. METHODS: In the 19 patients selected for this study unilateral temporal lobe surgery was performed. To investigate the course of bilateral interictal epileptiform discharges observed before surgery in awake or sleep over the temporal lobe contralateral to surgery, 24 h mobile 12 channel EEG recording was performed at minimum two, in average 4.6 (2-10) years after the surgery. RESULTS: The association of postoperative contralateral spikes and non-seizure free outcome was highly significant. The existence of unilateral pathology before surgery was highly predictive for good outcome and disappearance of contralateral spikes. The association between good seizure outcome, disappearance of contralateral spikes and the existence of unilateral pathology before surgery was also significant. Our data partially satisfies the expectations of both the "seizure induced" and mirror type secondary epileptogenesis hypotheses concerning origin of contralateral spikes, but were not completely congruent with either of them. CONCLUSIONS: Unfavourable surgical outcome in a temporal lobe epilepsy group with preoperative independent bilateral interictal spikes was associated with the persistence of postoperative contralateral spikes and lack of unilateral pathology. Compared with seizure outcome the presence/absence and distribution of postoperative interictal spikes in NREM sleep not entirely fit to the predictions of existing secondary epileptogenesis hypotheses.     

Hippocampal subfield segmentation in temporal lobe epilepsy: Relation to outcomes

Objective

To investigate the clinical and surgical outcome correlates of preoperative hippocampal subfield volumes in patients with refractory temporal lobe epilepsy (TLE) using a new magnetic resonance imaging (MRI) multisequence segmentation technique.

Methods

We recruited 106 patients with TLE and hippocampal sclerosis (HS) who underwent conventional T1‐weighted and T2 short TI inversion recovery MRI. An automated hippocampal segmentation algorithm was used to identify twelve subfields in each hippocampus. A total of 76 patients underwent amygdalohippocampectomy and postoperative seizure outcome assessment using the standardized ILAE classification. Semiquantitative hippocampal internal architecture (HIA) ratings were correlated with hippocampal subfield volumes.

Results

Patients with left TLE had smaller volumes of the contralateral presubiculum and hippocampus‐amygdala transition area compared to those with right TLE. Patients with right TLE had reduced contralateral hippocampal tail volumes and improved outcomes. In all patients, there were no significant relationships between hippocampal subfield volumes and clinical variables such as duration and age at onset of epilepsy. There were no significant differences in any hippocampal subfield volumes between patients who were rendered seizure free and those with persistent postoperative seizure symptoms. Ipsilateral but not contralateral HIA ratings were significantly correlated with gross hippocampal and subfield volumes.

Conclusions

Our results suggest that ipsilateral hippocampal subfield volumes are not related to the chronicity/severity of TLE. We did not find any hippocampal subfield volume or HIA rating differences in patients with optimal and unfavorable outcomes. In patients with TLE and HS, sophisticated analysis of hippocampal architecture on MRI may have limited value for prediction of postoperative outcome.     

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

PURPOSE: Although temporal lobe epilepsy (TLE) patients with dominant hemisphere hippocampal sclerosis generally have good cognitive outcome after anterior temporal lobectomy (ATL), a minority of patients experience at least mild post-ATL decline on one or more standardized measures of episodic and semantic memory. The goal of this investigation was to determine whether memory outcome in this group could be predicted from preoperative intracarotid amobarbital procedure (IAP) recognition memory scores. METHODS: Data from 22 left TLE patients were studied retrospectively. All were left hemisphere language dominant and had IAP scores for each hemisphere, a significant degree of pathology-confirmed left hippocampal sclerosis (HS+), and no positive MRI findings other than atrophy. Cognitive outcome status was represented by the number of pre- to post-ATL declines across three tests, as defined by 90th percentile Reliable Change Index (RCI) criteria. RESULTS: Only 14% of the sample exhibited decline on more than one memory test. Low right IAP (left hemisphere injection) scores and relatively high preoperative cognitive ability and age at surgery predicted a greater risk of post-ATL memory decline. CONCLUSIONS: A minority of left TLE HS+ patients experience at least a mild degree of RCI-defined decline in episodic or semantic memory after ATL. The right hemisphere IAP memory score, which reflects the functional reserve of the contralateral hemisphere, can help predict the risk of postoperative memory decline for TLE patients in whom HS+ is likely based on the presence of hippocampal atrophy on MRI or early age of seizure onset.     

颞叶癫痫MR海马容积测量

目的：测量正常成人及颞叶癫痫病人海马体积，讨论其在颞叶癫痫（ＴＬＥ）致痫灶定侧中价值。方法：本组包括５２例正常成人和２６例颞叶癫痫病人，后者有２２例为顽固性癫痫。均作垂直于海马轴的冠状位ＳＥ序列Ｔ１加权像、ＴｕｒｂｏＳＥＴ２加权像，测量颞叶、海马体积和颞角、环池宽度，肉眼观察Ｔ２加权像海马信号强度改变。采用海马体积绝对值对ＴＬＥ定侧。结果：获取了正常成人海马体积。２２例ＴＬＥ海马体积缩小，其中３例为双侧性；６例海马硬化经手术、病理证实，１例体积正常且致痫灶位于海马周围者海马硬化轻。３例ＴＬＥ病人同侧前颞叶萎缩；部分ＴＬＥ病侧颞角、环池宽度增加；萎缩明显的海马Ｔ２加权像信号弥漫性增高。结论：海马体积缩小、Ｔ２加权像信号弥漫性增高是海马硬化萎缩的直接征象，与病变严重程度、致痫灶在颞叶的部位有关。前颞叶萎缩和颞角、环池增宽是海马硬化的辅助征象     

Correlation of Scalp EEG and 1H-MRS Metabolic Abnormalities in Temporal Lobe Epilepsy

PURPOSE: To correlate the interictal spike field and region of seizure onset with the distribution of 1H-MRS abnormalities in temporal lobe epilepsy (TLE) and improve our understanding of the clinical significance of 1H-MRS abnormalities. METHODS: Scalp electroencephalogram (EEG) monitoring and proton magnetic resonance spectroscopy (1H-MRS) results were correlated in 31 consecutive patients with TLE. RESULTS: Lateralized 1H-MRS-based hippocampal abnormalities were recorded in 95% of the patients with unilateral interictal spikes, with a high degree of concordance for the lateralization side (90%). In 64% of the patients with normal or bilateral interictal EEG spikes, 1H-MRS provided lateralizing information. Bilateral 1H-MRS abnormalities, with or without lateralization, were 3 times more frequent than bitemporal EEG spikes. Anterior predominance of the 1H-MRS abnormalities was more frequent in patients with anterior temporal EEG spiking (50%), than in patients without this EEG distribution (18%). Similar association was noted between distribution of 1H-MRS abnormalities and region of EEG seizure onset. CONCLUSIONS: Our results show a moderate level of concordance between the distribution of 1H-MRS and EEG abnormalities. 1H-MRS identifies abnormalities contralateral to the predominant seizure focus more often than does EEG and may provide lateralizing information in patients with nonlateralizing interictal EEG.     

Ictal chronology and interictal spikes predict perfusion patterns in temporal lobe epilepsy: a multivariate study.

Typical (TPP) and atypical (APP) perfusion patterns (PP) may be seen in ictal SPECT of patients with temporal lobe epilepsy (TLE). APP may pose problem in the lateralization of the epileptogenic zone (EZ). We aimed to investigate predictive variables for the occurrence of TPP and APP. Fifty-one TLE patients were submitted to successful anterior-mesial temporal lobectomy. Univariate (UVA) and multivariate (MVA) analysis were performed upon clinical data, distribution of interictal spikes, and ictal chronology of seizures. From MVA, a final predictive model (FPM) was determined to better predict TPP and APP. Forty patients showed TPP (78.5%) and 11 patients APP (21.5%). Accuracy of ictal SPECT was higher in the unilateral (UIS) than in the bilateral (BIS) interictal spikes group (P = 0.05). FPM showed that patients exhibiting BIS, with shorter proportion of the electrographic seizure occurring after completion of tracer injection, and longer clinical than EEG seizure duration had more APP (P = 0.003). Generalized tonic-clonic seizures did not result in more APP. We concluded that analysis of ictal SPECT in TLE requires the knowledge of TPP and APP, the distribution of interictal spikes on temporal lobes and the ictal chronology of seizures. BIS showed that beyond a more complex epileptogenicity and seizure propagation, they may also lead to APP.     

Microscopic mild focal cortical dysplasia in temporal lobe dual pathology: An electrocorticography study

BackgroundAssociations between electrophysiological and histological findings might provide an insight into the epileptogenicity of mild focal cortical dysplasia (FCD) in patients with temporal lobe epilepsy (TLE) and a dual pathology.Subjects and methodsA total of 22 patients with pharmacoresistant TLE were included in the study, 16 of them with histologically confirmed hippocampal sclerosis (HS) associated with neocortical temporal mild Palmini Type-I FCD subtypes and 6 with HS. Intraoperative electrocorticography (ECoG) recordings were analysed for epileptiform discharge frequency and morphology. Associations between histological, and electrocorticography pattern findings in these patients were analysed. Electroclinical outcomes in these patients were also evaluated.ResultsNeocortical areas with mild Palmini Type-I FCD showed a significantly higher spike frequency (SF) recorded in the inferior temporal gyrus than those neocortical areas in patients with HS. There was a tendency to higher spike frequency and lower amplitude in neocortical areas with histopathologic subtype IB FCD in relation with IA during intraoperative ECoG. Post-SF excision and amplitude were significantly lower during neocortical post-excision intraoperative ECoG than during neocortical pre-excision recording. There was no difference found in the clinical outcome between patients with and without FCD.ConclusionsIntraoperative electrocorticographic interictal spike frequency recorded in the neocortical inferior temporal gyrus may help to characterize the histopathologic subtypes of mild Palmini Type-I FCD in patients with temporal lobe epilepsy (TLE) and a dual pathology. Our data support the epileptogenicity of neocortical mild FCD in TLE and assessments of ECoG patterns are relevant to determine the extent of the resection in these patients which can influence the electroclinical outcome.     

Short echo time single-voxel 1H magnetic resonance spectroscopy in magnetic resonance imaging-negative temporal lobe epilepsy: different biochemical profile compared with hippocampal sclerosis

Single-voxel proton magnetic resonance spectroscopy (1H MRS) has shown abnormalities in patients with temporal lobe epilepsy (TLE) and hippocampal sclerosis (HS). Many TLE patients, however, do not have HS or other lesions on quantitative magnetic resonance imaging (MRI) (MRI-negative). Fifteen control subjects, 15 patients with unilateral HS, and 15 MRI-negative TLE patients underwent 1H MRS at an echo time of 30 msec on a 1.5-T GE Signa scanner. Voxels were tailored to the individual hippocampi. N-Acetylaspartate (NAA), creatine, choline, total glutamate plus glutamine (Glx), and myo-inositol (Ins) were quantitated by using an external standard and LCModel, a user-independent quantitation method. Normal ranges were defined as the control mean +/- 2.5 SD. In HS patients, 12 of 15 had abnormally low NAA in sclerotic hippocampi; 3 of these 12 also had abnormally low NAA contralaterally. Abnormally low NAA/Ins ratios lateralized the side affected by HS in 7 of 15 patients, without any bilateral abnormalities. In 15 MRI-negative TLE patients, 4 had abnormally low hippocampal NAA ipsilateral to seizure onset, 1 of whom had abnormally low NAA bilaterally. Analysis of groups of subjects showed a bilateral decrease in NAA, most marked in patients with HS and on the side of seizure onset. The mean NAA/Ins ratio was lower in patients with HS than in control subjects and in MRI-negative patients. The concentration of Glx was higher ipsilateral to seizure onset in MRI-negative patients than in HS patients. Quantitative short echo time 1H MRS identified abnormalities in 87% of patients with HS and 27% of MRI-negative TLE patients in concordance with other lateralizing data. In individual and group comparisons, 1H MRS described a metabolite profile in the hippocampi of MRI-negative TLE patients that was different from patients with HS, with an increase in Glx and a less marked decrease in NAA than was seen in HS.     

Correlation of single photon emission computed tomography with pathology and seizure outcome in children undergoing epilepsy surgery

Introduction:  Single photon emission computed tomography (SPECT) imaging regional cerebral blood flow (rCBF) can help localize the seizure focus in partial epilepsies during presurgical evaluation. Few studies have explored the possible relationship between preoperative SPECT and underlying pathology, or any relationship to postsurgical outcome.
Study group:  Thirty-five children with medically intractable epilepsy undergoing resective surgery between the ages of 11 months and 18 years had presurgical ictal and interictal rCBF and post surgery follow up of 3–6 years.
Results:  Pathological examination revealed 13 to have hippocampal sclerosis (HS): of these 11 had relatively low interictal rCBF perfusion on the side of seizure onset, and eight had hyperfusion ictally. Eight children had morphological evidence of cortical dysplasia: all had a localizing ictal rCBF concordant with the area resected whereas only six demonstrated localized reduction in perfusion on interictal rCBF. All three patients with Rasmussens encephalitis had informative rCBF scans, concordant with the seizure focus. However, infarct, tumours and nonspecific pathology demonstrated poor localization of the seizure focus. No SPECT parameter correlated independently with outcome, although overall the HS group had the best outcome, particularly those with localizing ictal SPECT.
Comment:  Ictal SPECT appears predictive of underlying cortical dysplasia. Although in this small group of HS in children, ictal SPECT added little to interictal SPECT for seizure localization, it may be useful in the prediction of outcome. SPECT adds little to the evaluation of children being considered for hemispherectomy over and above the abnormalities detectable on MRI scan.     

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.     

Interictal EEG in temporal lobe epilepsy in childhood.

The authors clarified the value of interictal discharges and verified which extratemporal regions may also show epileptiform activity in temporal lobe epilepsy (TLE) in childhood. Thirty consecutive patients aged 3 to 18 years (mean age = 12.16 years; 16 male) with TLE associated with hippocampal atrophy were studied. Each patient had 1 to 15 interictal EEG recordings (mean: 5.6; total = 192 EEGs). Video-EEG monitoring was performed in 20 patients. All patients had MRI. The findings were compared with a control group of 53 consecutive TLE adult outpatients with hippocampal atrophy. Each adult patient underwent 3 to 21 routine EEGs (mean: 10.67; total = 566). Interictal EEGs of children with TLE showed extratemporal epileptiform discharges more frequently than EEGs of adults with TLE. Frontal, parietal, and occipital discharges were more frequently seen in children (P < 0.05). These results suggest a close interaction between temporal and other cerebral regions in children with epilepsy and provide further evidence of the existence of neural networks.     

Interictal temporal delta activity in temporal lobe epilepsy: correlations with pathology and outcome

PURPOSE: To determine the characteristics and the clinical significance of focal slow activity and its association with focal epileptogenesis in patients with temporal lobe epilepsy (TLE). METHODS: We analyzed the interictal EEGs of 141 patients who had temporal lobe resections for intractable focal seizures and correlated the findings with pathologic changes and outcome. The pathologic changes were categorized into medial temporal sclerosis, tumors, and nonspecific changes. RESULTS: Lateralized slow activity was found in 66% of the patients, and it was mainly temporal, of delta frequency and irregular morphology. None of its characteristics, including quantity and reactivity to eye opening, was substrate specific. It was highly concordant with temporal spiking (60%), without any difference across the three groups, but provided additional information in 19 (15%) patients who had no lateralizing spikes. The effect of sleep also was similar in all three groups and included transition of slow waves into spikes. Lateralized slow activity to the side of the operation was significantly associated with favorable outcome only in the group with nonspecific pathology (p = 0.008), regardless of the presence, laterality, or topography of spikes. CONCLUSIONS: Our findings suggest that in patients with TLE whose brain magnetic resonance imaging (MRI) is either normal or suggestive of medial temporal sclerosis, interictal temporal slow activity has a lateralizing value similar to that of temporal spiking. Its association with a favorable outcome in patients with nonspecific pathology also suggests that candidates with lateralizing temporal delta and normal MRI should not be barred from further preoperative assessment.     

Correlation of SPECT with pathology and seizure outcome in children undergoing epilepsy surgery

SPECT can be used to image regional cerebral blood flow (rCBF) and has been shown to help localize the seizure focus in partial epilepsies as part of the presurgical evaluation. Few studies have explored the possible relation between preoperative SPECT and underlying pathology, or any relation to postsurgical outcome. In this study preoperative ictal and interictal rCBF in relation to the histopathological diagnosis and outcome in a series of 35 children (24 females, 11 males; mean age 9.6 years, age range 11 months to 18 years) who had undergone resective surgery for epilepsy were retrospectively evaluated. A correlation between ictal hyperperfusion and the underlying responsible pathology was shown, with a consistent ictal increase in perfusion in developmental pathologies and Rasmussen's encephalitis, and consistent interictal hypoperfusion in hippocampal sclerosis (HS). No rCBF study parameter appeared to relate to outcome but in the group with HS the best outcome was seen in those with localizing ictal rCBF. The varied group of pathologies from hemispherectomy had excellent outcome but the SPECT findings had little to contribute over the abnormalities detected on MRI. In conclusion, rCBF studies remain a useful presurgical investigation in children with partial epilepsy, especially where HS, cortical dysplasia, or inflammatory disease are the underlying pathology. However, rCBF studies add little to the investigation of children with seizures secondary to benign tumours or cerebral infarcts, or where hemispherectomy is the likely preferred surgical option.