Electrographic Localization Research Articles

Bihemispheric Seizure Without Generalization.

A 70-year-old male without prior psychiatric history presented with recurrent episodes (<60seconds each, every 5-10minutes) of left hemibody and right lower extremity jerking movements concerning for seizure with preserved awareness (Video). Examination showed left hemiparesis (leg > arm) in addition to right lower extremity weakness. Computed tomography showed a right parafalcine acute subdural hematoma (SDH). Clinical events did not recur after intravenous lorazepam (4mg) and levetiracetam load (3500mg), and his weakness improved. He was continued on levetiracetam and has since remained seizure free for 16months. A 60-minute awake/sleep electroencephalogram (EEG) obtained 12hours after administration of antiseizure medications showed low amplitude theta slowing (posterior predominant) in the range of 5-7Hz. There was no apparent epileptiform activity or other abnormalities during the awake and sleep recording or photic stimulation. Focal seizures originate from pathologic disruption of neuronal activity within an isolated brain region, almost exclusively from a single hemisphere. Focal seizures may generalize bilaterally with associated impaired awareness. This is the first visual report demonstrating focal, bihemispheric clinical seizures, without generalization or impaired awareness. Rarely patients with generalized motor involvement from seizures have had retained consciousness and memory. The parafalcine SDH likely promoted epileptogenicity of the bilateral hemispheres. Acute and chronic SDH commonly present with seizures. Although there were no supportive electrographic findings, parasagittal epileptogenic lesions may be difficult for both clinical and electrographic localization. Post-event paresis with clinical improvement in the hours after event cessation supports clinical seizure.

Contemporaneous evaluation of patient experience, surgical strategy, and seizure outcomes in patients undergoing stereoelectroencephalography or subdural electrode monitoring.

Intracranial electrographic localization of the seizure onset zone (SOZ) can guide surgical approaches for medically refractory epilepsy patients, especially when the presurgical workup is discordant or functional cortical mapping is required. Minimally invasive stereotactic placement of depth electrodes, stereoelectroencephalography (SEEG), has garnered increasing use, but limited data exist to evaluate its postoperative outcomes in the context of the contemporaneous availability of both SEEG and subdural electrode (SDE) monitoring. We aimed to assess the patient experience, surgical intervention, and seizure outcomes associated with these two epileptic focus mapping techniques during a period of rapid adoption of neuromodulatory and ablative epilepsy treatments. We retrospectively reviewed 66 consecutive adult intracranial electrode monitoring cases at our institution between 2014 and 2017. Monitoring was performed with either SEEG (n=47) or SDEs (n=19). Both groups had high rates of SOZ identification (SEEG 91.5%, SDE 88.2%, P=.69). The majority of patients achieved Engel class I (SEEG 29.3%, SDE 35.3%) or II outcomes (SEEG 31.7%, SDE 29.4%) after epilepsy surgery, with no significant difference between groups (P=.79). SEEG patients reported lower median pain scores (P=.03) and required less narcotic pain medication (median = 94.5 vs 594.6 milligram morphine equivalents, P=.0003). Both groups had low rates of symptomatic hemorrhage (SEEG 0%, SDE 5.3%, P=.11). On multivariate logistic regression, undergoing resection or ablation (vs responsive neurostimulation/vagus nerve stimulation) was the only significant independent predictor of a favorable outcome (adjusted odds ratio = 25.4, 95% confidence interval = 3.48-185.7, P=.001). Although both SEEG and SDE monitoring result in favorable seizure control, SEEG has the advantage of superior pain control, decreased narcotic usage, and lack of routine need for intensive care unit stay. Despite a heterogenous collection of epileptic semiologies, seizure outcome was associated with the therapeutic surgical modality and not the intracranial monitoring technique. The potential for an improved postoperative experience makes SEEG a promising method for intracranial electrode monitoring.

Invasive electroencephalography monitoring: Indications and presurgical planning.

Electroencephalography (EEG) remains a “gold standard” for defining seizures; hence identification of epileptogenic zone for surgical treatment of epilepsy requires precise electrographic localization of the seizures. Routine scalp EEG recording is not sufficient in many instances, such as extratemporal lobe epilepsy or non-lesional temporal lobe epilepsy. In these individuals EEG recording from proximity of the seizure focus is necessary, which can be achieved by placing electrodes on the surface or in the substance of the brain. As this process requires invasive procedures (usually necessitating surgical intervention) EEG obtained via these electrodes is defined as invasive electroencephalography (iEEG). As only limited areas of the brain can be covered by these electrodes in an individual, precise targeting of the presumed seizure onset location is crucial. The presurgical planning includes where to place electrodes, which type of the electrodes to choose and planned duration of the intracranial recording. Though there are general principles that guide such endeavor, each center does it slightly differently depending upon the various technologies available to them and expertise and preferences of the epilepsy surgery team. Here we describe our approach to iEEG recording. We briefly describe the background, types of iEEG recording and rationale for each, various electrode types, and scenarios where iEEG might be useful. We also describe planning of iEEG recording once the need has been established as well as our decision making process of deciding about location of electrode placement, type of electrodes to use, length of recording, choice of arrays, mapping of eloquent cortex and finally surgical planning and decisions.

Stereoelectroencephalography in the “difficult to localize” refractory focal epilepsy: Early experience from a North American epilepsy center

Stereo-electroencephalography (SEEG) enables precise recordings from deep cortical structures, multiple noncontiguous lobes, as well as bilateral explorations while avoiding large craniotomies. Despite a long reported successful record, its application in the United States has not been widely adopted. We report on our initial experience with the SEEG methodology in the extraoperative mapping of refractory focal epilepsy in patients who were not considered optimal surgical candidates for other methods of invasive monitoring. We focused on the applied surgical technique and its utility and efficacy in this subgroup of patients. Between March 2009 and May 2011, 100 patients with the diagnosis of medically refractory focal epilepsy who were not considered optimal candidates for subdural grids and strips placement underwent SEEG implantation at Cleveland Clinic Epilepsy Center. Demographics, noninvasive clinical data, number and location of implanted electrodes, electrophysiologic localization of the epileptic zone, complications, and short-term seizure outcome after resection were prospectively collected and analyzed. Mean age was 32 years (range 5-68 years); 54 were male and 46 female. The mean follow-up after resection was 15 months. In total, 1,310 electrodes were implanted. Analyses of the SEEG recordings resulted in the electrographic localization of the epileptogenic focus in 96 patients. In the group of 75 patients who underwent resection, only 53 had at least 12 months follow-up. From this group, 33 patients (62.3%) were seizure-free at the end of the follow-up period. The presence of abnormal pathologic finding was strongly associated with postoperative seizure control (p = 0.005). The risk of hemorrhagic complications per electrode was 0.2%. In patients who are not considered to be ideal candidates for subdural grids and strips implantation, the SEEG methodology is a safe, useful and reliable alternative option for invasive monitoring in patients with refractory focal epilepsy, providing an additional mean for seizure localization and control in a "difficult to localize" subgroup of patients.

Combination of Ictal EEG and Seizure Semiology Provides 24-Hour Seizure Susceptibility Profile (P04.018)

Objective: To investigate the occurrence of seizures based on sleep/wake status and electrographic localization in pediatric epilepsy. Background We previously described diurnal and sleep/wake patterns of seizures based on clinical presentation and electrographic localization. In this study, we investigated in a larger patient series whether the sleep/wake state of seizure onset can predict EEG localization of seizures with different semiology. Design/Methods: Charts of 955 consecutive patients with epilepsy undergoing continuous video-EEG monitoring were reviewed for EEG localization, seizure occurrence out of wakefulness or sleep and for clinical seizure type. Seizures were characterized according to 2001 ILAE terminology. Proportions were compared using binomial methods. Odds ratios were used to compare seizure localization based sleep/wake state. Results: 407 patients aged 0-21 (194 girls, mean age 9.2 ± 6.0 years) had 1,754 seizures. The majority of seizures occurred out of wakefulness (58%, p Conclusions: Sleep/wake states at seizure onset can predict EEG localization of seizures with certain semiology. Clonic, dyscognitive and myoclonic seizures have more likely a generalized EEG onset when occurring during wakefulness, and a focal EEG onset when occurring out of sleep. Disclosure: Dr. Ramgopal has nothing to disclose. Dr. Loddenkemper has received personal compensation for activities with Eisai Inc. as a consultant. Dr. Loddenkemper has received research support from NIH/NINDS, The Epilepsy Foundation of America, CIMIT/DOD, Harvard Medical School Office of Faculty Development, and the Children9s Hospital Program for Patient Safety and Quality Improvement. Dr. Vendrame has nothing to disclose. Dr. Shah has nothing to disclose. Dr. Zarowski has nothing to disclose. Dr. Alexopoulos has received personal compensation for activities with UCB Pharma as a speaker. Dr. Wyllie has nothing to disclose. Dr. Kothare has nothing to disclose.

The use of positron emission tomography in the clinical assessment of epilepsy

Positron emission tomography (PET) of local cerebral glucose utilization is highly sensitive in detecting epileptogenic regions that correspond to electrographic localization in patients with epilepsy. In medically refractory temporal lobe epilepsy for which surgical resection of the epileptogenic zone is a therapeutic option, the application of PET enables more than 50% of adults and older children to be successfully operated on without the necessity for chronic intracranial electrographic monitoring. In infants with intractable infantile spasms and various types of partial epilepsy, PET has uncovered focal areas of cortical dysplasia and other anatomic abnormalities, which, after resection, have resulted in cessation of seizures and developmental improvement. The distribution of PET abnormality is in excellent agreement with the extent of the epileptogenic zone as determined by intraoperative electrocorticography, thus avoiding the necessity for chronic intracranial electrographic monitoring in 90% of these infants. As a result of PET, the preoperative evaluation of intractable epilepsy in both adults and children has become less invasive and less costly.

Functional Brain Imaging in Pediatrics

With the development of noninvasive tomographic imaging techniques, it is now possible to measure local chemical and physiologic functions in various body organs. Studies of local cerebral glucose metabolism in infants and children using positron emission tomography (PET) have provided important information on human brain functional development and plasticity. The clinical application of functional neuroimaging techniques in the management of pediatric neurologic disorders has yielded encouraging results. In children with intractable epilepsy being considered for surgical intervention, PET is highly sensitive in localizing focal areas of cortical dysplasia, heterotopias, and other migrational defects corresponding to surface electrographic localization of epileptogenic regions. Expanding PET technology provides a new approach that holds great promise in the diagnosis and management of brain disorders in children.

Patterns of postictal cerebral blood flow in temporal lobe epilepsy

We used single-photon emission computed tomography (SPECT) to study postictal cerebral blood flow (CBF) in 51 patients with temporal lobe epilepsy. There were 78 seizures studied, 77 by early postictal injection of Tc-99m HMPAO (delay from seizure onset = 4.3 +/- 4.5 min) and one by ictal injection. Increased focal temporal lobe uptake, predominantly confined to the anteromesial region, was present in 83% and declined rapidly over 5 minutes. Reduced activity in the lateral temporal lobe accompanied the mesial increase in 80% of studies, extending over much of the ipsilateral hemisphere and closely associated with the degree and extent of postictal EEG slow waves. These patterns enabled correct seizure localization by blinded analysis in 69% (31/45) of the patients with a unilateral EEG focus. The remainder showed bilateral or no changes. One of six patients with bitemporal EEG foci had unilateral perfusion changes. The positive predictive value for the correct localization of a unilateral focus by postictal SPECT was 97% (31/32). Postictal CBF imaging with SPECT can be used to support noninvasive electrographic localization and may decrease the need for invasive electrode studies.

Pathology of temporal lobe foci

Twenty-six patients with medically refractory complex partial seizures had temporal lobectomy after evaluation, which included prolonged scalp EEG recordings, positron emission tomography (PET), MRI, and x-ray CT. PET showed a region of focal interictal temporal hypometabolism corresponding to electrographic localization of seizure onset in 21. Five patients had a region of increased MRI signal intensity on the spin echo image in the region of the EEG focus, 2 had an abnormality ipsilateral to but distinct from the EEG focus, and 1 had bilateral findings. CT was abnormal in 3 cases; 2 had tumors. Three patients had low grade tumors (1 with a normal PET). PET can detect metabolic dysfunction associated with mild pathologic changes in epileptic foci, but increased signal intensity on MRI does not necessarily correlate with the degree of pathologic abnormality. Tumors may be less likely when both CT and MRI are normal.