Electrophysiological study of intractable epileptogenicity in human epilepsy: clinical usefulness of ictal DC shifts and cavernous sinus EEG]

In order to clarify the clinical and electrophysiological features in intractable epileptogenicity in human epilepsy, we applied the new techniques, ictal DC shifts and cavernous sinus EEG recording, for presurgical evaluation of patients with intractable partial epilepsy. (1) Ictal DC shifts were successfully recorded with subdural electrodes in 8 patients with intractable neocortical epilepsy, and an analysis of ictal DC shifts would add useful information to delineate an epileptogenic area. Scalp-recorded ictal DC shifts were also investigated in 3 patients with intractable neocortical epilepsy. It also delineated the epileptogenic area, but it was vulnerable for artifacts. (2) By using the techniques of intravascular EEG recording, we recorded EEG from the bilateral cavernous sinus (cavernous sinus EEG) in patients with intractable temporal lobe epilepsy. Cavernous sinus EEG well sensitively recorded interictal, also ictal in selected patients, epileptiform discharges which arose from the mesial temporal structure even though they were not recorded by scalp electrodes. It is concluded that the above two techniques are clinically useful for delineating an epileptogenic area in patients with neocortical epilepsy and temporal lobe epilepsy.     

颅内电极脑电监测定位致癇灶

目的探讨颅内埋置电极脑电图(iEEG)监测定位致灶的意义及其安全性。方法对38例经无创方法难以定位的难治性癫病人,采用颅骨钻孔或骨瓣开颅方法埋置硬膜下和(或)深部电极,行长程视频脑电监测定位致灶。根据术中致灶定位、术后病理、术后疗效和EEG复查结果分析iEEG监测定位致灶的准确性。结果8例埋置深部电极,13例埋置硬膜下电极,17例联合应用硬膜下电极和深部电极。颅内电极埋置4～22d,平均9d;脑电监测8～226 h,平均128h。根据癫发作初始期iEEG,32例(84.2%)病人准确定位了致灶,无颅内出血和感染等严重并发症发生。结论选择性应用硬膜下和深部电极长程视频脑电监测是一种安全、有效的检查方法;癫发作初始期异常放电的节律和范围是可靠的致灶定位指标。     

Dynamic changes of ictal high-frequency oscillations in neocortical epilepsy: using multiple band frequency analysis

PURPOSE: To characterize the spatial and temporal course of ictal high-frequency oscillations (HFOs) recorded by subdural EEG in children with intractable neocortical epilepsy. METHODS: We retrospectively studied nine children (four girls, five boys; 4-17 yr) who presented with intractable extrahippocampal localization-related epilepsy and who underwent extraoperative video subdural EEG (1000 Hz sampling rate) and cortical resection. We performed multiple band frequency analysis (MBFA) to evaluate the frequency, time course, and distribution of ictal HFOs. We compared ictal HFO changes before and after clinical onset and postsurgical seizure outcomes. RESULTS: Seventy-eight of 79 seizures showed HFOs. We observed wide-band HFOs ( approximately 250 Hz, approximately 120 electrodes) in six patients either with partial seizures alone (three patients) or with epileptic spasms (three patients). Three patients with partial seizures that secondarily generalized had wide-band HFOs ( approximately 170 Hz) before clinical onset and sustained narrow-band HFOs (60-164 Hz) with electrodecremental events after clinical onset ( approximately 28 electrodes). In four postoperatively seizure-free patients, more electrodes recorded higher-frequency HFOs inside the resection area than outside before and after clinical seizure onset. In five patients with residual seizures, electrodes recorded more HFOs that were of higher or equal frequency outside the surgical area than inside after clinical onset. CONCLUSION: For partial seizures alone and epileptic spasms, more electrodes recorded only wide-band HFOs; for partial seizures that secondarily generalized, fewer electrodes recorded wide-band HFOs, but in these seizures electrodes also recorded subsequent sustained narrow-band ictal HFOs. Resection of those brain regions having electrodes with ictal, higher HFOs resulted in postsurgical seizure-free outcomes.     

SECTION D: NEUROSURGERY & NEUROPATHOLOGY

Comparison of surgical and medical treatment for partial epilepsy. Medical and social implications of the treatment
Procedures in Pediatric Epilepsy Surgery
The possible need for intra-cranial EEG in surgery for temporal lobe epilepsy
Consistency of lateralisation in intracranial record-ings of seizures of temporal lobe origin
Comparison of lateralising capability of 99Tc^m HM-PAO-SPECT, neuropsychology, interictal and ictal EEG in the pre-surgical evaluation of patients with intractable epilepsy
Convergence of CT/MRI, "FDG-PET, intracarotid amobarbital procedure and D.EEG in presurgical evaluation of refractory partial epilepsy
Surgery for epilepsy in the United Kingdom
Anterior 2/3 callosotomy for the treatment of in-tractable epilepsy
Pre-surgical EEG evaluation
A simplified technique for epidural recording of epi-leptiform activity and seizure patterns
Discrepancy between interictal and ictal EEG-find-ings - the use of subdural electrodes may solve the problem
Temporal mesiolimbic versus temporal neocortical complex partial seizures; electroclinical correlates recorded by combined depth and subdural electrodes
Verifying electrical dipole localization in patients with epilepsy undergoing depth EEG recordings in the presurgical evaluation of intractable epilepsy
A current dipole tracing method locating interictal epileptiform activity in patients with focal epilepsy
PET-studies on distribution of glia in patients with focal epilepsy
Relationship of pre-operative neuropsychological test to the sodium amytal test - results on an empiri-cal study
Amygdalohippocampectomy in complex partial epi-lepsy     

Ictal SPECT in Nonlesional Extratemporal Epilepsy

Summary:  Purpose: Ictal single-photon emission computed tomography (SPECT) may be a reliable indicator of the ictal onset zone in patients with intractable partial epilepsy who are being considered for epilepsy surgery. The rationale for the illustrated case report is to evaluate the use of an innovation in SPECT imaging in a patient with nonlesional extratemporal epilepsy.
Methods: We investigated the presurgical evaluation and operative outcome in a patient with intractable partial epilepsy. The ictal semiology indicated a "hypermotor" seizure with bipedal automatism. The electroclinical correlation and magnetic resonance imaging (MRI) did not suggest the appropriate localization of the epileptogenic zone. A subtraction periictal SPECT coregistered to MRI (SISCOM) was peformed.
Results: SISCOM revealed a region of localized hyperperfusion in the right supplementary sensorimotor area. Chronic intracranial EEG monitoring confirmed the relationship between the localized SISCOM alteration and the ictal onset zone. The patient was rendered seizure free after surgical treatment.
Conclusions: SISCOM may be used to identify potential candidates for surgical treatment of nonlesional extratemporal epilepsy. Periictal imaging may also alter the strategy for intracranial EEG recordings and focal cortical resection.     

Quantitative interictal subdural EEG analyses in children with neocortical epilepsy

PURPOSE: We studied the relation between quantitative interictal subdural EEG data and visually defined ictal subdural EEG findings in children with intractable neocortical epilepsy, and determined whether interictal EEG data are predictive of ictal EEG onset zones. METHODS: Thirteen children (aged 1.2-15.4 years) underwent prolonged intracranial EEG recording, using 48- to 120-channel subdural electrodes. Three distinct 10-min segments of the continuous interictal EEG recording were selected for each patient, and the spike frequency for each channel was determined by using an automatic spike-detection program. Subsequently the average spike frequency of each electrode was compared with ictal assessment (onset, spread, and no early ictal involvement). In addition, 50 distinct interictal spikes were averaged for each patient, and the amplitude and latency after the leading spike (averaged spike showing the earliest peak) were measured for each electrode and analyzed with respect to ictal EEG findings. RESULTS: Reproducibility of the spike-frequency pattern derived from three 10-min segments was high (Kendall's W, 0.85 +/- 0.08). Electrodes showing the highest spike frequency, the highest spike amplitude, and the leading spike were found to be a part of the seizure onset in 13 of 13, 12 of 13, and 10 of 13 cases, respectively. There was significant correlation between ictal assessment and spike frequency as well as spike amplitude. A receiver operating characteristics analysis showed that a cutoff threshold at 14% of the maximal spike frequency resulted in a specificity of 0.90 and a sensitivity of 0.77 for the detection of seizure-onset electrodes. CONCLUSIONS: Quantitative interictal subdural EEG may predict ictal-onset zones in children with intractable neocortical epilepsy.     

Topographic movie of ictal high-frequency oscillations on the brain surface using subdural EEG in neocortical epilepsy

PURPOSE: To understand the rapid dynamic changes of ictal intracranial high-frequency oscillations (HFOs) in neocortical epilepsy. METHODS: We integrated multiple band frequency analysis and brain-surface topographic maps of HFOs from ictal subdural EEG (SDEEG) recordings. We used SDEEG to record partial seizures consisting of right-arm jerks with secondary generalization in a 17-year-old right-handed girl. We selected 20-s EEG sections that included preclinical seizure recordings. We averaged the HFO power between 60 and 120 Hz for 25 selected electrodes, made topographic maps from these averaged powers, and superimposed the maps on the brain-surface image. We filmed consecutive HFO maps at a 10-ms frame rate. RESULTS: Before clinical seizure onset, high-power HFOs emerged at the superior portion of the left precentral gyrus, then appeared in the middle of the left postcentral gyrus, and subsequently reverberated between both regions as well as the posterior portion of the left postcentral gyrus. Right-arm extension and facial grimacing started as the HFO power decreased. As generalized tonic-clonic seizures evolved, HFO power increased but remained within the central region. CONCLUSIONS: Topographic movies of intracranial HFOs on the brain surface allow visualization of the dynamic ictal changes in neocortical epilepsy.     

Paradoxical lateralization of non-invasive electroencephalographic ictal patterns in extra-temporal epilepsies

Video-electroencephalographic (EEG) ictal recordings play an important role in the pre-surgical evaluation of patients with medically refractory focal epilepsy. Paradoxical lateralization of the scalp EEG ictal onset patterns, consistently contralateral to the side of the proven epileptogenic lesion is rare but important to recognize, with possible implications on patient management. We searched the database of the University of Munich Epilepsy Monitoring Unit for patients with extratemporal epilepsies, with scalp EEG ictal patterns consistently contralateral to the proven epileptogenic zone. All available clinical, EEG and imaging data were reviewed. Dipole source analysis of EEG seizure onset was performed where possible. Four patients were identified, who had proven paradoxical lateralization of scalp EEG ictal patterns, demonstrated by seizure freedom after epilepsy surgery, data from invasive electroencephalography, or imaging and seizure semiology. Parasagittal lesions on MRI brain scan were found in three cases. Invasive recordings with subdural electrodes were performed in one patient. Dipole source analysis of EEG seizure onset was possible in two patients, helping to correctly lateralize the ictal EEG pattern in one patient. Patients with midline or near midline neocortical seizure foci may show paradoxical lateralization of the ictal EEG, likely due to the spatial orientation of the cortical generators in the medial regions of the cerebral hemispheres. These patients may have excellent surgical outcome despite the apparently discordant EEG findings, making this an important phenomenon to be recognized in clinical practice.     

Chronic Intracranial EEG Monitoring for Localizing the Epileptogenic Zone: An Electroclinical Correlation

Summary: Purpose: To evaluate the diagnostic yield and identify predictive factors of the surgical outcome in patients with intractable partial epilepsy undergoing chronic intracranial EEG monitoring (CIEM).
Methods: The clinical, magnetic resonance imaging (MRI) and electrophysiologic data of 108 patients that underwent CIEM were retrospectively reviewed. The discharge pattern and spatial extent of the initial ictal discharge were determined by blinded visual inspection and computerized analysis.
Results: The main predictive indicator for epilepsy surgery outcome in patients that underwent CIEM was the presurgical MRI findings. Most patients with hippocampal atrophy or complete lesionectomy were rendered seizure free after epilepsy surgery (83 and 80%, respectively), whereas only a small minority of patients with partial lesipectomy or no detected MRI lesion had seizure–free operative outcomes (21 and 22%, respectively). Multifocal independent initiation of the initial ictal discharge was associated with a poor surgical outcome. In contrast, the pattern and local spatial extent of the initial ictal discharge observed with CIEM failed to predict the surgical outcome.
Conclusions: The main predictor of the surgical outcome in patients that underwent CIEM was the MRI findings, whereas CIEM had only limited use in localizing the epileptogenic zone in the absence of an MRI lesion. The reported findings indicate a low specificity of CIEM in defining the site of seizure onset, which in turn significantly impairs the reliability of CIEM in delineating the epileptogenic zone for epilepsy surgery. Further studies are required to define the indications and patient sub–populations who can benefit from CIEM before epilepsy surgery.     

Quantitative visualization of ictal subdural EEG changes in children with neocortical focal seizures

OBJECTIVE: To quantify the ictal subdural electroencephalogram (EEG) changes using spectral analysis, and to delineate the quantitatively defined ictal onset zones on high-resolution 3D MR images in children with intractable neocortical epilepsy. METHODS: Fourteen children with intractable neocortical epilepsy (age: 1-16 years) who had subsequent resective surgery were retrospectively studied. The subjects underwent a high-resolution MRI and prolonged subdural EEG recording. Spectral analysis was applied to 3 habitual focal seizures. After fast Fourier transformation of the EEG epoch at ictal onset, an amplitude spectral curve (square root of the power spectral curve) was created for each electrode. The EEG magnitude of ictal rhythmic discharges was defined as the area under the amplitude spectral curve within a preset frequency band including the ictal discharge frequency, and calculated for each electrode. The topography mapping of ictal EEG magnitude was subsequently displayed on a surface-rendered MRI. Finally, receiver operating characteristic (ROC) analysis was performed to evaluate the consistency between quantitatively and visually defined ictal onset zones. RESULTS: The electrode showing the maximum of the averaged ictal EEG magnitude was part of the visually defined ictal onset zone in all cases. ROC analyses demonstrated that electrodes showing >30% of the maximum of the averaged ictal EEG magnitude had a specificity of 0.90 and a sensitivity of 0.74 for the concordance with visually defined ictal onset zones. SIGNIFICANCE: Quantitative ictal subdural EEG analysis using spectral analysis may supplement conventional visual inspection in children with neocortical epilepsy by providing an objective definition of the onset zone and its simple visualization on the patient's MRI.     

The clinical usefulness of ictal surface EEG in neocortical epilepsy

PURPOSE: Localizable scalp EEGs, during ictal episodes, appear to be rare in neocortical epileptic syndromes. However, studies based on large numbers of patients are also rare. This study aims to identify the characteristic patterns of variable neocortical epilepsies and to evaluate their clinical usefulness in the localization of epileptogenic focuses. METHODS: We retrospectively assessed 394 noninvasive ictal recordings from 86 patients who subsequently underwent invasive study and resective surgery. Ictal EEGs were recorded using a video-EEG monitoring system with electrodes placed according to the International 10-20 system, with additional anterior temporal electrodes. The ictal recordings were analyzed according to localizing accuracy and frequency characteristics. The durations of discrete or regional ictal rhythms were also measured. RESULTS: The percentage of discrete or regional EEGs was 23% in frontal lobe epilepsy, 52% in lateral temporal lobe epilepsy, 70% in occipital lobe epilepsy, and 10% in parietal lobe epilepsy. In order of frequency, the localizable ictal rhythms were theta, beta, alpha, delta, and rhythmic spike-and-wave. The duration of discrete or regional ictal rhythms was significantly shorter in frontal lobe epilepsy and parietal lobe epilepsy than in other epilepsies. Ictal beta activity was the most common rhythm in discrete-patterned EEGs. Structural lesions found on MRI did not significantly affect the localization of epileptogenic focuses in the patients. The type of seizure was not related to the degree of localization, with the exception of simple partial seizure. CONCLUSIONS: Ictal surface EEG was clinically helpful in the localization of epileptogenic focuses in at least some neocortical epileptic syndromes.     

Indications and outcome of ictal recording with intracerebral and subdural electrodes in refractory complex partial seizures.

Intracranial electrophysiologic recording has often been used to localize ictal onset zones in presurgical evaluation of refractory complex partial seizures. Specific indications for intracranial ictal monitoring have not been analyzed in detail, however. The authors designed this study to test the utility of intracranial monitoring in specific indications and considered six specific indications for intracranial monitoring. They compared prospectively determined indications and outcomes of chronic intracerebral and subdural electrophysiologic recording in 50 consecutive patients whose ictal onset zones had been inadequately localized with interictal and ictal EEG using extracranial electrodes, magnetic resonance imaging, interictal[18F]fluorodeoxyglucose positron emission tomography, and neuropsychological testing. In 47 patients ictal onset zones were localized with intracranial recordings, leading to resections in 38 patients. Each indication for intracranial monitoring selected a group in which the majority went on to have efficacious epilepsy surgery (5-year follow-up). Definitive diagnosis of bilateral independent ictal onset zones in temporal lobe epilepsy required intracranial ictal EEG. Intracranial EEG localization supported efficacious resection in most patients, despite contradictory or nonlocalizing extracranial ictal EEG and neuroimaging abnormalities. Critical analysis of these specific indications for intracranial monitoring may be useful in multicenter evaluation of these techniques.     

Spatial localization and time-dependant changes of electrographic high frequency oscillations in human temporal lobe epilepsy

Purpose:   High frequency oscillations (HFOs) >200 Hz are believed to be associated with epileptic processes. The spatial distribution of HFOs and their evolution over time leading up to seizure onset is unknown. Also, recording HFOs through conventional intracranial electrodes is not well established. We therefore wished to determine whether HFOs could be recorded using commercially available depth macroelectrodes. We also examined the spatial distribution and temporal progression of HFOs during the transition to seizure activity.
Methods:   Intracranial electroencephalography (EEG) recordings of 19 seizures were obtained from seven patients with temporal lobe epilepsy using commercial depth or subdural electrodes. EEG recordings were analyzed for frequency content in five spectral bands spanning DC-500 Hz. We examined the spatial distribution of the different spectral bands 5 s before and 5 s after seizure onset. Temporal changes in the spectral bands were studied in the 30-s period leading up to seizure onset.
Results:   Three main observations were made. First, HFOs (100–500 Hz) can be recorded using commercial depth and subdural grid electrodes. Second, HFOs, but not <100 Hz oscillations, were localized to channels of ictal onset (100–200, 400–500 Hz, p < 0.05; 300–400 Hz, p < 0.001). Third, temporal analysis showed increased HFO power for approximately 8 s prior to electrographic onset (p < 0.05).
Conclusions:   These results suggest that HFOs can be recorded by depth macroelectrodes. Also, HFOs are localized to the region of primary ictal onset and can exhibit increased power during the transition to seizure. Thus, HFOs likely represent important precursors to seizure initiation.     

Ictal patterns of neocortical seizures monitored with intracranial electrodes: correlation with surgical outcome

PURPOSE: Numerous factors have been analyzed in attempts to predict the outcome of surgical resections in patients with neocortical epilepsy. We examined the correlation between surgical outcome and electrocorticographic features of neocortical ictal patterns. METHODS: Twenty six patients with neocortical epilepsy underwent monitoring with subdural grid electrodes before surgery. Ictal patterns were analyzed retrospectively and correlated with three types of outcome: seizure free, worthwhile improvement (>75% reduction of seizure frequency), and no worthwhile improvement. The duration of follow-up was 2-5 years. RESULTS: Ictal patterns were divided according to the size of epileptogenic zone (focal, regional, multifocal); velocity and type of seizure propagation (fast contiguous, slow contiguous, noncontiguous); pattern of the onset of ictal activity; part of the cortex involved in the origin of the seizure (frontal, frontocentroparietal, etc.). Spread to medial temporal structures (as assessed by subtemporal strips) also was evaluated in selected cases. Statistically significant correlation with surgical outcome (p = 0.026) was shown for only one variable: type of spread. Patients with slow spread (n = 8) demonstrated the best outcomes (five are seizure free), whereas patients with noncontiguous spread (n = 5) demonstrated the worst outcomes (four did not improve significantly). Patients with fast contiguous spread (n = 13) showed intermediate outcomes. CONCLUSIONS: Types of propagation of ictal neocortical activity correlate with surgical outcome. Analysis of ictal pattern during intracranial recordings may help to predict surgical outcome for neocortical epilepsy.     

Tailored resections in occipital lobe epilepsy surgery guided by monitoring with subdural electrodes: characteristics and outcome

PURPOSE: Occipital lobe epilepsy is uncommon in epilepsy surgery series and often difficult to assess due to rapid seizure propagation, misleading seizure semiology and confounding interictal epileptiform activity. Ictal recordings with surface electrodes may not define properly the seizure onset zone in surgical evaluation for intractable occipital epilepsy. Specially in dysplastic lesions, the extension of the epileptogenic zone is not well defined by neuroimaging techniques, therefore, implantation of intracranial electrodes is often indicated. In this study we present our experience with individually tailored resections of occipital lobe epileptic foci guided by monitoring with subdural electrodes. METHODS: Data from interictal and ictal surface and intracranial recordings, neuroimaging, surgical treatment, pathology and outcome of seven patients are presented. RESULTS: The most common seizure type (6/7 patients) was complex partial with temporal lobe semiology, five patients experienced visual auras as part of their complex partial seizures or as separate simple partial seizures. Two patients had seizures suggesting supplementary motor area involvement. One patient had temporal as well as frontal seizure propagation. Neuroimaging showed lesions in 6/7 patients. Pathological studies revealed cortical dysplasia and tumors as the most common causes. Intracranial recordings (6/7 patients) revealed focal onset in 2 patients, regional onset in 2, and diffuse onset in 2. Surgery was performed according to intracranial recordings restricting resections in cases with focal seizure onset (even in large dysplastic lesions) and performing wider resections in patients with regional or diffuse onset. Five of seven patients are seizure free after 12-55 months (mean 24.3). The two remaining patients may be classified as Engel 2b and 3a. CONCLUSIONS: This series of occipital lobe epilepsy surgery shows that, even in patients with cortical dysplasias, restricted resections may have a good outcome and that intracranial monitoring is usually necessary in order to design an individually tailored resection.     

颅内电极埋藏在Lennox-Gastaut综合症中的应用(附10例临床分析)

目的探讨颅内电极埋藏术后进行视频脑电图评估在癫痫外科手术致痫灶定位困难的Lennox-Gastaut综合症中的使用。方法收集10例Lennox-Gastaut综合症致痫灶定位困难的患者,向颅内硬膜下植入条状电极,术后进行视频脑电图评估,记录发作间歇期及发作期脑电图变化,确定癫痫病灶的起始区,通过手术方式切除致痫灶。结果本组10例患者埋藏时间为2～7天,平均4天,均记录到间歇期及发作期脑电图情况。根据脑电图结果,行脑叶切除及胼胝体切开。术后按照Engel评分I级4例,II级2例,III级2例,IV级2例。所有病例均未出现埋藏电极引起的严重并发症。结论在致痫灶定位困难的Lennox-Gastaut综合症中,采用颅内电极埋藏进行视频脑电图检测,可以较准确定位主要致痫灶,从而提高Lennox-Gastaut综合症外科治疗有效率。     

Interictal PET and ictal subtraction SPECT: Sensitivity in the detection of seizure foci in patients with medically intractable epilepsy

Purpose: Interictal positron emission tomography (PET) and ictal subtraction single photon emission computed tomography (SPECT) of the brain have been shown to be valuable tests in the presurgical evaluation of epilepsy. To determine the relative utility of these methods in the localization of seizure foci, we compared interictal PET and ictal subtraction SPECT to subdural and depth electrode recordings in patients with medically intractable epilepsy. Methods: Between 2003 and 2009, clinical information on all patients at our institution undergoing intracranial electroencephalography (EEG) monitoring was charted in a prospectively recorded database. Patients who underwent preoperative interictal PET and ictal subtraction SPECT were selected from this database. Patient characteristics and the findings on preoperative interictal PET and ictal subtraction SPECT were analyzed. Sensitivity of detection of seizure foci for each modality, as compared to intracranial EEG monitoring, was calculated. Key Findings: Fifty‐three patients underwent intracranial EEG monitoring with preoperative interictal PET and ictal subtraction SPECT scans. The average patient age was 32.7 years (median 32 years, range 1–60 years). Twenty‐seven patients had findings of reduced metabolism on interictal PET scan, whereas all 53 patients studied demonstrated a region of relative hyperperfusion on ictal subtraction SPECT suggestive of an epileptogenic zone. Intracranial EEG monitoring identified a single seizure focus in 45 patients, with 39 eventually undergoing resective surgery. Of the 45 patients in whom a seizure focus was localized, PET scan identified the same region in 25 cases (56% sensitivity) and SPECT in 39 cases (87% sensitivity). Intracranial EEG was concordant with at least one study in 41 cases (91%) and both studies in 23 cases (51%). In 16 (80%) of 20 cases where PET did not correlate with intracranial EEG, the SPECT study was concordant. Conversely, PET and intracranial EEG were concordant in two (33%) of the six cases where the SPECT did not demonstrate the seizure focus outlined by intracranial EEG. Thirty‐three patients had surgical resection and >2 years of follow‐up, and 21 of these (64%) had Engel class 1 outcome. No significant effect of imaging concordance on seizure outcome was seen. Significance: Interictal PET and ictal subtraction SPECT studies can provide important information in the preoperative evaluation of medically intractable epilepsy. Of the two studies, ictal subtraction SPECT appears to be the more sensitive. When both studies are used together, however, they can provide complementary information.     

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.     

Scalp-Recorded, Ictal Focal DC Shift in a Patient with Tonic Seizure

Summary: Purpose: We recorded focal ictal DC shifts from scalp electrodes in a 9–year-old boy with intractable, clinically generalized tonic seizures. The patient had a high intensity signal abnormality of the left temporal cortex with thickening of the gyri on T2–weighted MRI. Methods: Scalp digital EEGs were recorded using electrodes made of silver/silver chloride. The low frequency filter (LFF) was set at 0.016 Hz. Recorded seizures were subsequently analyzed with LFF settings of 1.0, 0.016 and 0.03 Hz. Results: All recorded seizures initially showed diffuse, low voltage, high frequency activity (electrodecremental pattern) followed 10–20 s later by quasirhythmic activity over the left frontotemporal region. In two seizures, LFF of 0.016–0.03 Hz revealed a slow negative shift over the left frontotemporal area simultaneously with onset of the bilateral electrodecremental pattern. However, in the other seizures, this initial slow negative shift was obscured by artifacts. Subsequent electrocorticography (ECoG) delineated frequent epileptiform discharges in the left temporal as well as frontal cortex. Conclusions: Scalp-recorded ictal DC shifts may help identify focal epileptogenic brain area in patients with clinically generalized seizures although the technique is vulnerable to artifact.     

RTTBD‐like activity in association with hippocampal ictal discharges in patients with temporal lobe epilepsy

Aim. To determine clinical and intracranial EEG correlates of rhythmic temporal theta bursts of drowsiness (RTTBD) and assess its clinical significance in patients with temporal lobe epilepsy (TLE). Methods. A retrospective review of simultaneous scalp and intracranial video‐EEG recordings from 28 patients with TLE was evaluated for epilepsy surgery. Scalp RTTBD patterns were identified and their clinical and intracranial EEG correlates were then determined on video‐EEG recording using depth and subdural electrodes. Results. Thirty‐one RTTBD patterns on scalp EEG were observed in six (21%) of the 28 patients. Five (16%) of the RTTBD patterns occurred during wakefulness and 26 (84%) occurred during drowsiness and light sleep. The mean duration of RTTBD was 10 seconds (range: 3‐28 seconds). RTTDB consistently correlated with hippocampal ictal discharges and was time‐locked to the hippocampal seizures in which the ictal discharges evolved into rhythmic theta frequency (4‐7‐Hz) range. Ictal automatisms were observed during five (16%) RTTBD patterns, while cognitive impairment was observed in four (13%) of the 31 RTTBD patterns. Conclusion. Our findings show that scalp EEG correlates of hippocampal ictal discharges can resemble RTTBD and may be associated with ictal symptoms and cognitive impairment, indicating that RTTBD may rarely be an ictal EEG pattern in patients with TLE.