Summary:Purpose: We wished to determine whether continuous EEG source imaging can predict the location of seizure onset with sublobar accuracy in temporal lobe epilepsy (TLE).Methods: We retrospectively analyzed the earliest scalp ictal rhythms, recorded with 23-to 27-channel EEG, in 40 patients with intractable TLE. A continuous source analysis technique with multiple fixed dipoles (Focus 1.1) decomposed the EEG into source components representing the activity of major cortical sublobar surfaces. For the temporal lobe, these were basal, anterior tip, anterolateral, and posterolateral cortex. Ictal EEG onset was categorized according to its most prominent and leading source component. All patients underwent intracranial EEG studies before epilepsy surgery, and all had a successful surgical outcome (follow-up >1 year).Results: Most patients with ictal rhythms having a predominant basal source component had hippocampal-onset seizures, whereas those with seizures with prominent lateral source activity had predominantly temporal neocortical seizure origins. Seizures with a prominent anterior temporal tip source component mostly had onset in entorhinal cortex. Seizures in some patients had several equally large and nearly synchronous source components. These seizures, which could be modeled equally well by a single oblique dipole, had onset predominantly in either entorhinal or lateral temporal cortex. Conclusions:Multiple fixed dipole analysis of scalp EEG can provide information about the origin of temporal lobe seizures that is useful in presurgical planning. In particular, it can reliably distinguish seizures of mesial temporal origin from those of lateral temporal origin. Key Words: Electroencephalography-Dipole-Seizures-Temporal lobe epilepsy.Ictal rhythms are believed to be more reliable than interictal spikes in localizing the epileptogenic focus (1,2). Traditional methods of interpreting scalp ictal EEG have been descriptive and based on the simplistic p i nciple that the electrodes recording the clearest rhythm overlie the seizure focus. Some investigators have noted a correlation among scalp ictal EEG patterns (e.g., frequency and evolution) and intracranial seizure origins in the temporal lobe (3-6). We believe that, as has been shown for interictal spikes (7-15), source analysis of the voltage fields of scalp ictal rhythms can provide more information concerning seizure origin and propagation than can visual inspection of EEG traces.Dipole source modeling is one method of estimating the character of cerebral sources underlying a scalp voltage field (16)(17)(18)(19). This mathematical technique attempts to find a theoretical dipole source that can produce a voltage field on a model head that is equivalent to the

Summary:Purpose: We evaluated visual patterns and source localization of ictal magnetoencephalography (MEG) in patients with intractable temporal lobe epilepsy (TLE) and extratemporal epilepsy (ETE).Methods: We performed spike and seizure recording simultaneously with EEG and MEG on two patients with TLE and five patients with ETE. Scalp EEG was recorded from 21 channels (10-20 international system), whereas MEG was recorded from two 37-channel sensors. We compared ictal EEG and MEG onset, frequency, and evolution and performed MEG dipole source localization of interictal spikes and early ictal discharges and coregistered dipoles to brain magnetic resonance imaging (MRI). We correlated dipole characteristics with intracranial EEG, surgical resection, and outcome.Results: Ictal MEG lateralized seizure onset in both TLE patients and demonstrated ictal onset, frequency, and evolution in accordance with EEG. Ictal MEG source analysis revealed tangential vertical dipoles in the anterolateral angle in one patient, and anterior dipoles with anteroposterior orientation in the other. Intracranial EEG revealed regional entorhinal seizure onset in the first patient. Both patients became seizure free after temporal lobectomy. In ETE, ictal MEG demonstrated visual patterns similar to ictal EEG and had concordant localization with interictal MEG in all five patients. Two patients underwent surgery. Ictal MEG localization was concordant with intracranial EEG in both cases. One patient had successful outcome after surgery. The second patient did not improve after limited resection and multiple subpial transections.Conclusions: Ictal MEG can demonstrate ictal onset frequency and evolution and provide useful localizing information before epilepsy surgery. Key Words: MEG-IctalTemporal-Extratemporal-Epilepsy.Source-localization techniques of EEG and magnetoencephalography (MEG) in epilepsy have been useful in providing noninvasive localizing information in evaluating intractable temporal lobe epilepsy (TLE) and extratemporal epilepsy (ETE) for epilepsy surgery (1). Many studies have demonstrated the value of MEG source localization of interictal spikes in determining the seizure focus in TLE (2-17) and ETE (13-18). Ictal rhythms, however, are believed to have more localizing value than do interictal spikes (19,20). Ictal MEG recording is rare because many MEG studies have been performed on epilepsy outpatients with therapeutic anticonvulsant (AED) levels and because of the logistic difficulty with prolonged patient recording in the MEG laboratory (1). Thus only limited reports exist of ictal MEG recordings of seizures in intractable TLE and ETE (21-25).Sutherling et al. (21) with TLE and two other patients with ETE and concluded that ictal MEG and EEG discharges have a similar frequency. Stefan et al. (22) reported on interictal and ictal MEG recording from three patients, of whom two patients had TLE, and one patient had frontal lobe epilepsy. The source localization by MEG was concordant with electrocorticography and imaging stu...

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Summary: Purpose; We investigated whether visual and quantitative ictal EEG analysis could predict surgical outcome after anteromesial temporal lobectomy (AMTL) in which mesial structures, basal, and temporal tip cortex were resected.Methods: We retrospectively reviewed 282 presurgical scalprecorded ictal EEGs (21-to 27-channel) from 75 patients who underwent AMTL. We examined the pattern of seizure onset (frequency, distribution, and evolution) and estimated the principal underlying cerebral generators by using a multiple fixed dipole model that decomposes temporal lobe activity into four sublobar sources (Focus 1.1). We correlated findings with a 2-year postoperative outcome.Results: Sixteen patients had seizures with a well-lateralized, regular 5 to 9-Hz rhythm at onset, that most often had a temporal or subtemporal distribution. All patients became seizure free after surgery. In 5 I patients, seizure onset was remarkable for lateralized slow rhythms (<5 Hz), which sometimes appeared as periodic discharges, were often irregular and stable only for short periods (<5 s), and had a widespread lateral temporal distribution. Among these a favorable surgical outcome was encountered in patients with seizures having prominent anterior-tip sources (16 of 17 seizure free), whereas those with dominant lateral or oblique sources had a less favorable outcome (three of 14 and 13 of 18, respectively). Irregular, nonlateralized slowing characterized seizure onsets in eight patients. Three patients became seizure free after surgery.Conclusions: Both visual and quantitative sublobar source analysis of scalp ictal EEG can predict surgical outcome in most cases after AMTL and complement non-invasive presurgical evaluation.

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