Postoperative EEG Research Articles

Anterior Corpus Callosotomy in the Treatment of Medically Intractable Epilepsy: Multicenter Study in Japan

Purpose: Corpus callosotomy has been extensively used in the past 25 ycars Tor the treatment of patients with medically intractable epilepsy who do not qualify for resective surgery. However, several issues remain controversial; i.e., the criteria for patient selection, the timing of the operation, the extent of the callosal division, and the significance of postoperativc EEG changes. We report on the results of anterior corpus callosotomy (ACC) in 53 intractable seizure patients undertaken in a multiccnter analysis in Japan to define predictive outcome factors. Methods: 53 patients with more than I year postoperative follow‐up (mean 43.2 months) were included. Age at the time of operation ranged from 5 to 44 years (mean 19.9), and age at the onset of epilepsy ranged from 0.3 to 23 years (mean 6.3). Preoperative diagnoses were cryptogenic or symptomatic generalized epilepsy (SGE) (34 patients), frontal lobe epilepsy (FLE) (17 patients), and severe myoclonic epilepsy in infancy (2 patients). Seizure outcome at the time of the most recent follow‐up was classified into 5 classes: Free, with complete elimination of seizure; Excellent, with >SO% reduction in seizure frequency; Good, with >50% reduction in seizure frequency;: Poor, with no significant change; Worse, with worsening of seizures and / or unacceptable neurological deficit. The relationships between outcome and clinical factors such as epileptic syndrome, seizure type, age at surgery, age of onset, duration of epilepsy, preoperative IQ, extent of callosol division, and postoperative EEG changes were analyzed. Results: 36 of 53 patients (67.9%) showed significant improvement after the surgery. The outcome was seizure free in 4 (7.576), excellent in 18 (34.0%), good in 14 (26.4%), and poor in 17 patienfs (32.1%). There was no worse case, Four seizure‐free patients were included in pediatric group (under 15 years). 70.6% of the patients with SGE and 64.7% of those with FLE showed a significant improvement. In addition, 1 each of the 2 patients with SME showed a good and poor outcome, respectively. Significant improvement occurred in 70%‐80% of all the seizure types except for simple partial seizure (40.0%) andcomplex partial seizure (46.7%). Complete elimination of seizure was obtained in 38.1 % of drop attack, 33.3% of generalized tonic‐clonic seizure, 33.3% of myoclonic seizure. 30.0% of partial seizure with secondary generalization, and 27.8% of atypical absence. None of the clinical factors correlated significantly with the outcome cxcept for a shorter duration of epilepsy in the seizure free patients. A tzndency of a better outcome was observed in the pediatric group (p =0.093), when seizure onset was after age 1 (p=0.339), in those with a higher IQ (p = 0. I38), and when there was a disappearance or lateralizetion of thc slow spike and wave to the unilateral hemisphere on postoperative EEG (p = 0.159). There was no clear relationships between the extent of the callosal division and the outcome. Conclusion: The results suggest that ACC is most profitably performed during the early stage of illness, except in those patients with seizure onset before age 1 associated with severe brain dysfunction. Availability of a chronological developmental IQ during infancy and computer analysis of generalized epileptiform activity prior to surgery will likely improve the quality of case selection and therefore, the surgical outcome.

Discontinuation of antiepileptic drugs after successful epilepsy surgery.

To evaluate the frequency and risk factors for seizure recurrence subsequent to antiepileptic drug (AED) withdrawal in patients who underwent surgical treatment for intractable partial epilepsy and were rendered seizure-free. The outcome of discontinuation of AED medication was studied retrospectively in 210 consecutive patients who were rendered seizure-free after epilepsy surgery performed between 1989 and 1993. Medical therapy was reduced in 96 patients and discontinued in 84 patients. The seizure recurrence rate after complete AED withdrawal was 14% and 36% at 2 and 5 years. In contrast, only 3% and 7% of the 30 patients who did not alter AED treatment after surgery had recurrent seizures in the same time intervals. After AED discontinuation, seizures tended to recur more often in patients with normal preoperative MRI studies compared with those with focal pathology. However, this difference did not reach significance. Intraoperative electrocorticography, extent of surgical resection, postoperative EEG, and seizure-free duration after surgery were not predictive of seizure outcome after AED withdrawal. AED withdrawal was associated with seizure recurrence in a significant portion of patients rendered seizure-free by epilepsy surgery. Patients with a normal preoperative MRI study showed a tendency for higher seizure recurrence, whereas the duration of seizure-free postoperative AED treatment interval did not significantly influence the seizure recurrence rate. These results will prove useful in counseling patients about discontinuing AED treatment after successful epilepsy surgery.

Middle Fossa Approach in Vestibular Schwannoma Surgery. Postoperative Hearing Preservation and EEG Changes

When the middle fossa (MF) approach was introduced in Denmark, we were concerned about the possible risk to the temporal lobe caused by the retraction of the lobe when exposing the internal acoustic meatus. EEG recordings were therefore obtained prospectively before (21 patients) and after MF tumor removal (all 23 patients operated from 1989 to 1997). Only three patients had normal EEG recordings before and after surgery, while 86% had induction, or worsening, of focal and paroxystic activity, even at the last follow-up (median 3.5 years). Sixteen patients operated prospectively via the translabyrinthine (TL) also had pre- and postoperative EEG and served as a control group. Only minor EEG changes were found in this group. In neither group did the patients display any clinical neurological signs (seizures). At the latest evaluation the facial function was reduced in 8 patients (35%) with 6 patients going 1 step up the scale, 1 patient 2 steps up and 1 patient 3 steps up (from HB-1 to HB-4). The integrity of the facial nerve was maintained in all patients. Postoperatively, 10 patients (44%) had useful hearing (hearing class A and B) on the operated side. Four patients had anacusis and an additional 4 patients were reduced to hearing class D with very low PTA and SDS. In total, 9 patients (39%) retained their preoperative hearing class, while 14 patients (61%) had impairment in their hearing class. In conclusion, EEG changes (low frequency activity and IEA) may be provoked or worsened as part of the middle cranial fossa procedure. The mechanism is not fully known, but may reflect peroperative pressure on the temporal lobe. EEG changes are fewer and lighter in translabyrinthine-operated patients. The practical clinical implications of the possibility of developing EEG changes, even without clinical signs, are potentially serious, and must be included in the information given to the patients before surgery.

The significance of bilateral EEG abnormalities before and after hemispherectomy in children with unilateral major hemisphere lesions.

The rate of seizure relief following hemispherectomy varies between 50 and more than 80%. There has been particular debate concerning the significance of bilateral electroencephalography (EEG) abnormalities in influencing prognosis. This study was set out to determine the frequency of bilateral EEG abnormalities and their relationship to underlying pathology and outcome. We investigated 28 children with unilateral hemisphere lesions, who underwent hemispherectomy. Interictal and ictal EEGs before and after hemispherectomy were reviewed. Post-operative outcome with respect to seizures was noted. Bilateral EEG abnormalities were seen in 75%, but were more common in children with malformations of cortical development than in patients with acquired cerebral lesions, and were found more often in interictal than in ictal records. Post-operative EEG abnormalities were variable and did not consistently predict outcome. Short-term outcome was similar, irrespective of aetiology. With longer term follow-up, only 47% of children with developmental abnormalities were still seizure-free in contrast to 77% of children with acquired abnormalities. Although the incidence of bilateral EEG abnormalities in patients with major unilateral hemisphere lesions is high, these findings alone should not preclude further consideration for hemispherectomy. Our findings emphasise that the aetiology of the lesion plays a major role in determining outcome.

Ganglioglioma and intractable epilepsy: clinical and neurophysiologic features and predictors of outcome after surgery.

To review the clinical, neurophysiologic, and radiological data of patients with ganglioglioma who had undergone evaluation and surgery in our Epilepsy Program. The medical and neurophysiologic records of 38 patients with intractable epilepsy and ganglioglioma were reviewed. Data underwent statistical analysis. There were 28 temporal and 10 extratemporal resections, with a mean age at seizure onset of 10.5 years and mean age at surgery of 22 years. Five tumor resections performed earlier were recorded. Twenty-nine patients had auras and 20 had secondarily generalized seizures. All 28 patients with temporal tumor had complex partial seizures. Preoperative MRI demonstrated the tumor in 36 of 36 patients: 17 of 29 demonstrated gadolinium enhancement, and 17 of 36 had mass effect. Scalp interictal sharp waves were present in 32 patients, and in 15 they were multiregional. In two patients, scalp EEG seizure onset was from the hemisphere contralateral to the tumor. Postoperatively, 79% of patients (30 of 38) were seizure-free (Engel's class I) at 6 months, 72% at 1 year (26 of 36), and 63% at 2 years (20 of 32). Excellent outcome was associated with a lower age at operation (p = 0.008), shorter duration of epilepsy (p = <0.01), absence of generalized seizures (p = <0.01), and no epileptiform discharges on a postoperative EEG (p = 0.01). Good surgical outcome is expected in patients with ganglioglioma despite years of medically resistant seizures. Good outcome may be achieved despite EEG findings that may conflict with tumor location, and is more likely when surgery is performed relatively soon after epilepsy onset.

Safety of intrahippocampal depth electrodes for presurgical evaluation of patients with intractable epilepsy.

Intracerebral depth electrodes are used in preoperative evaluation of selected patients with intractable epilepsies. In spite of their usefulness, safety of depth electrodes is disputed, and the number of insertions is decreasing. This study examined retrospectively possible deleterious effects such as perioperative complications, induction of epileptogenesis, and neuropsychologic deficits. Clinical course and neuroradiologic findings of 115 patients with bilaterally inserted longitudinal intrahippocampal depth electrodes (IDEs) were analyzed. Hippocampal resection specimens were examined histopathologically. To detect newly developed epileptogenic areas, EEG recordings, seizure control, and semiology after standardized resection procedures were compared between patients who received IDEs and those who did not. To demonstrate functional deficits caused by IDE insertion into an unaffected hippocampus of the speech-dominant hemisphere, changes of verbal learning and memory performances before and after right amygdalohippocampectomy were compared between patients evaluated with and without IDEs. Five significant complications without any permanent neurologic deficit were noted, and only one was specifically linked to IDE insertion. The tissue damage associated with the insertion was minimal and sharply circumscribed. No differences of seizure outcome after standardized resections were identified between patients with and without IDEs. In postoperative EEG recordings, there was no evidence of new epileptogenic areas. No verbal memory deficit caused by IDE implantation into the hippocampus of the speech-dominant hemisphere was detectable. Results indicate that it is safe to implant these IDEs in selected patients.

Multiple Subpial Transection for Control of Epileptic Seizures: Effectiveness and Safety

To assess the efficacy and safety of multiple subpial transection (MST), a new technique in epilepsy surgery, alone and in combination with resection. MST was performed in 22 patients with intractable epilepsy, 10 of whom were treated with a combination of a resection and MST in functionally important cortex, 6 of whom were treated with a combination of a resection and MST performed outside functionally important cortex, and 6 of whom were treated with MST alone. Of the 6 patients who received MST alone, none became seizure free and 4 showed > 50% reduction of all seizure types. In 2 patients, including 1 with Rasmussen's encephalitis, no change in seizure frequency or intensity occurred. Of the 16 patients in whom MST was combined with a resection, 9 (56%) became seizure free. Six of the remaining 7 patients showed > 95% reduction of all seizure types. Disappearance of epileptiform potentials in the postoperative EEG correlated significantly with complete relief from seizures. Subtle, permanent neurological deficits remained in 5 of 14 patients who received MST in functionally important brain areas. Reduction of the seizure frequency was substantial in 4 of 6 patients who received MST alone, but complete seizure control was not observed. MST surrounding a lesionectomy may be a new surgical approach which would minimize the excised volume and improve seizure control.

Fatal Paradoxical Cerebral Embolization during Bilateral Knee Arthroplasty

NEUROLOGIC complications of knee and hip arthroplasty range from mild delirium to coma and death. 1 The pathogenesis and operative events that lead to acute neurologic injury during joint arthroplasty are not completely understood but are thought to be a consequence of the fat embolism syndrome. 1-3 The syndrome often is accompanied by pulmonary, circulatory, hematologic, and neurologic derangement. According to one hypothesis, procedures that increase intramedullary pressure promote the entry of marrow fat or other debris into the central venous circulation through the medullary veins. 3,4 These emboli accumulate within the lung, causing increases in the pulmonary vascular resistance and pulmonary artery pressure. The consequent increase in right atrial and pulmonary artery pressures favor right-to-left shunt flow via a patent foramen ovale (atrial septal defect) or intrapulmonary shunt increasing the risk of paradoxical cerebral embolization. In the following report, intraoperative hemodynamic monitoring, carotid artery ultrasonography, and electroencephalography (EEG) were used to detect the sequence of operative events that led to paradoxical cerebral embolization causing fatal neurologic injury during bilateral knee arthroplasty.

EEG and Seizure Outcome After Epilepsy Surgery

The significance of the EEG after epilepsy surgery is not fully understood. We investigated the association between postoperative EEG abnormalities and persistent seizures after epilepsy surgery as they relate to pathologic lesions. Among 254 patients who underwent epilepsy surgery between 1987 and 1991, we identified 78 patients who had mesiotemporal sclerosis (MTS) and 47 patients who had low-grade brain tumors, all of whom had 6- to 18-month postoperative follow-up including EEG. Patients who had other pathology, multiple operations, callosotomy, or hemispherectomy, or who were aged < 18 years or who had insufficient EEG data, were excluded. Patients were classified as having persistent seizures or being seizure-free since operation. EEG abnormalities were abstracted from EEG reports 6-18 months postoperatively. Seizures persisted in 24% of the MTS group and in 27% of the tumor group. Of those with normal EEGs, none of the MTS patients and only 1 of the tumor patients had persistent seizures (p = 0.03 for MTS and p = 0.42 for tumor). Epileptiform discharges and focal slowing were associated with seizure persistence in both groups, but to a significant extent only in the MTS group. In the MTS group, patients who had both epileptiform discharges and focal slowing were more likely to have persistent seizures than were those with either abnormality alone.

Postoperative EEG and electrocorticography: relation to clinical outcome in patients with temporal lobe surgery.

To evaluate the role of different EEG methods with respect to postoperative clinical follow-up, 32 non-lesionary epilepsy patients who had undergone temporal lobectomy were studied preoperatively and at 2-week, 3-month, and 1-year postoperative follow-up. Routine, sleep, and sphenoidal EEG recordings as well as intraoperative electrocorticography (ECoG) were made for all patients. At 1-year follow-up, the EEGs with sphenoidal electrodes and with sleep deprivation procedure provided important prognostic information; the appearance of seizures was associated with the presence of interictal epileptiform abnormalities in EEG. In the postresection ECoG, however, epileptiform abnormalities were not associated with clinical outcome or with postoperative epileptiform EEG at 1 year. Routine EEG reliably reflects clinical outcome after temporal lobectomy; with sphenoidal electrodes as well as with sleep deprivation procedure, the diagnostic yield can be further improved.

Low-grade glial neoplasms and intractable partial epilepsy: efficacy of surgical treatment.

We performed a retrospective study of 51 consecutive patients who underwent operation for intractable partial epilepsy related to low-grade intracerebral neoplasms between 1984 and 1990. All patients had medically refractory partial seizures and a mass lesion identified on neuroimaging studies. Lesionectomy was performed on 17 patients, and 34 had lesion resection and corticectomy. Mean postoperative follow-up was 4.4 years (range 2-8 years). Sixty-six percent of patients were seizure-free, and 88% experienced a significant reduction in seizure frequency. In 16 patients (31%), antiepileptic drugs (AEDs) were successfully discontinued. Twenty-five of 31 (81%) eligible patients obtained a driver's license after successful operation. Patients with complete tumor resection and no interictal epileptiform activity on postoperative EEG studies had the best operative outcome. Epilepsy surgery can result in long-term improvement in seizure control and quality of life (QOL) in selected patients with intractable tumor-related epilepsy. Our results should be useful to clinicians considering treatment options for patients with intractable seizures related to low-grade intracerebral neoplasms.

The role of hemispherectomy in the treatment of holohemispheric hemimegaloencephaly.

The role of hemispherectomy in treating holohemispheric hemimegaloencephaly, a unilateral brain malformation, is still not well defined. The authors describe the cases of five infants presenting with intractable seizures, progressive neurological deficits, and severe developmental delay. Electroencephalography (EEG) showed generalized polyspikes from the megaloencephalic hemisphere and progressive slowing on the opposite side in all children; contralateral seizure spikes occurred in three children. Three of the five children underwent hemispherectomy for intractable seizures before 2 years of age, after which the seizures subsided completely in two children and improved remarkably in the third. Preoperative Wada testing proved useful in evaluating pharmacologically the effect of hemispherectomy on contralateral polyspikes. Postoperative EEG revealed the absence of polyspikes in the operated hemisphere and decreased slowing on the contralateral side. Psychomotor development in the surgically treated infants exceeded that of the children not undergoing hemispherectomy. Of the two children treated medically, one died at 4 years of age in status epilepticus and the other (now 5 years old) has frequent seizures and severe developmental delay. Based on these results, hemispherectomy appears to be a useful procedure for controlling seizures and improving psychomotor development in children with hemimegaloencephaly involving the entire hemisphere. Surgery in infancy can prevent or minimize seizure foci and encephalopathic changes that may develop in the contralateral hemisphere. Staging the procedure and exercising meticulous hemostasis make surgery relatively safe in infants who otherwise may have significant blood loss associated with increased blood flow to the megaloencephalic hemisphere.

Effect of anterior callosotomy on bilaterally synchronous spike and wave and other EEG discharges.

We analyzed pre- and postoperative interictal and ictal EEG patterns in relation to seizure outcome in 29 patients with intractable epilepsy who had undergone anterior callosotomy. Twenty-two patients had generalized bilaterally synchronous sharp or spike and slow wave discharges (GSW) and 7 did not: Postoperatively, patients with preoperative GSW showed disruption of synchrony, increased amplitude asymmetry, and a decreased amount of GSW. No significant decrease was noted in the amount of total epileptic discharge after operation. There was a significant relation between seizure outcome and decrease in amount of GSW. The degree of disruption of synchrony, total amount of epileptic discharge, and pre- and postoperative EEG patterns were not good indicators of seizure outcome. Postoperative changes in lateralization of epileptic foci consisted either of increased lateralization, less lateralization but increased independent discharges in the previously nonpredominant hemisphere, or appearance of some lateralization. There appears to be a spectrum of GSW: Both secondary bilateral synchrony and secondarily generalized corticoreticular epileptic discharges are distributed along this spectrum.

Significance of postoperative electroencephalograms in patients with extratemporal lesional epilepsy

We retrospectively studied EEGs performed 1 week, 3 months, and 1 year after surgery (lesionectomy or lesion resection with corticectomy) in 24 patients with extratemporal lesional epilepsy who had a mean duration of follow-up of 2.5 years. All patients had intractable partial seizures and underwent a comprehensive presurgical evaluation including long-term EEG monitoring. Twenty of the 24 patients had interictal epileptiform activity (IEA) identified on the preoperative sleep and awake EEG recordings. The presence of IEA 1 year after surgery was associated with recurrent seizure activity ( p < 0.05). The postoperative EEG recordings, however, revealed no IEA in the two patients with persistent seizures who had no epileptiform abnormality on the preoperative study. The extent of cortical resection appeared to have no significant effect on the recording of IEA after surgery. One-year postoperative EEG recordings are prognostically useful in patients with extratemporal lesional epilepsy who undergo surgical treatment.

Postoperative EEG studies: Relation to clinical outcome in patients with temporal lobe surgery

Postoperative EEG studies: Relation to clinical outcome in patients with temporal lobe surgery

Simulation of postoperative EEG after callosotomy for medically intractable epilepsy through multidimensional autoregressive analysis : H. Baba, K. Ono ∗, M. Yonekura. Nagasaki Chuo National Hospital, Nagasaki; ∗ Nagasaki University School of Medicine, Nagasaki

Simulation of postoperative EEG after callosotomy for medically intractable epilepsy through multidimensional autoregressive analysis : H. Baba, K. Ono ∗, M. Yonekura. Nagasaki Chuo National Hospital, Nagasaki; ∗ Nagasaki University School of Medicine, Nagasaki

Central nervous system function after cardiopulmonary bypass.

In a prospective study, an elderly group of patients (n = 63, 47 male, 16 female, age 40-65 years) was examined before and after open-heart surgery under cardiopulmonary bypass: postoperatively, 19 patients (30%) showed no clinical neuropsychiatric symptoms, whereas in 35 patients (56%) mild or transient neurological signs and in nine (14%) severe neurological complications were found. The postoperative EEG changes were characterized by a slight delta-theta increase, an alpha decrease and a significant slowing of the dominant frequency from 9.7 to 9.3 Hz. In brainstem auditory evoked potentials no changes were found, and in somatosensory evoked potentials (median nerve) the latency of the early cortical component, N20, increased. Cardiovascular reflexes showed increased changes, similar to those found in autonomic neuropathies. In the neuropsychological test battery, the Visual retention test (Benton) and the Rorschach test showed slight postoperative improvement, whereas other psychometric variables (flicker fusion frequency, reaction time) did not change. Despite an improved operative technique some minor clinical and neurophysiological disturbances of the central nervous system remain. However, specific pre- or peri-operative risk factors for these postoperative disturbances or complications could not be identified.

Surgical treatment for epilepsy in cerebral tuberous sclerosis.

Tuberous sclerosis (TS) is an autosomal dominant hamartiosis and hamartomatosis with variable expression that is commonly associated with medically intractable seizures. Patients with TS complex (TSC) frequently have multiple brain lesions that can give rise to seizure activity. We report 9 patients with TSC who underwent epilepsy surgery at the Mayo Clinic between 1986 and 1990. Surgical procedures performed included cortical resection (n = 2) and stereotaxic lesionectomy (n = 7). Neuropathologic diagnoses were cortical tubers (n = 7) and glioneural hamartomas (n = 2). Three of 9 patients had multifocal interictal scalp epileptiform EEG activity; however, ictal recordings identified the focus of seizure activity, which in all cases corresponded to a prominent neuroimaging abnormality. Our patients have been followed for 10-72 months (mean 35 months). Four patients are seizure-free with medication, 2 are seizure-free without medication, 2 had > 80% reduction in seizure frequency, and 1 experienced only an initial temporary reduction in seizure frequency. Postoperative EEG recordings showed absence of epileptiform abnormalities in the 5 patients who are seizure-free; the other 4 patients continue to have multifocal abnormalities. These data suggest that epilepsy surgery may be beneficial in selected patients with TSC despite multifocal EEG and neuroimaging abnormalities.

Long-term follow-up of stereotactic lesionectomy in partial epilepsy: predictive factors and electroencephalographic results.

We performed an extended follow-up study assessing the efficacy of stereotactic lesionectomy in 23 patients with foreign-tissue lesions and intractable partial epilepsy. Sixteen lesions involved functional or eloquent cortex as determined by anatomic localization. By definition, the surgical objective in these patients was excision of the lesion, and not the surrounding cerebral cortex. The mean duration of follow-up was 48.5 months (range 26-69 months). Seventeen patients (74%) had a significant reduction in seizures (greater than or equal to 90%) after lesionectomy. Thirteen patients (56%) had a class I operative outcome (seizure-free, single seizure episode, or auras only). Five of these patients were successfully discontinued from antiepileptic drug (AED) therapy. Patients with temporal lobe lesions were statistically less likely to be rendered seizure-free (p less than 0.05). Age at operation, duration of epilepsy, and underlying pathology were not significant predictors of seizure outcome. The anatomic distribution of extracranial EEG recorded epileptiform activity did not appear to be an important determinant of outcome. The absence of interictal epileptiform activity in the 3-month postoperative EEG correlated with a significant reduction in seizures. Long-term follow-up indicates that lesionectomy may be effective in select patients with medically refractory partial seizure disorders.

Significance of sharp waves in routine EEGs after epilepsy surgery.

We retrospectively analyzed the presence of sharp waves in 2-h EEGs performed 6 months after epilepsy surgery in 59 patients. To study the significance of the postoperative interictal epileptiform activity in the tissue remaining after resection, we included only patients with a single epileptic focus (as defined preoperatively by prolonged video/EEG recordings and subdural electrode arrays studies) and no progressive structural lesions. Temporal lobectomy was performed in 51 patients (86%); extratemporal resections were performed in the remainder. The epileptogenic focus was completely resected in 26 patients (44%). The immediate postoperative electrocorticograms (EcoG) showed spikes in 13 patients (22%). At 6-month follow-up, 43 patients (73%) were seizure-free or had auras only and 12 patients (20%) had epileptiform activity on EEG. A significant correlation was noted between presence of sharp waves in the 6-month postoperative EEG and recurrence of seizures (Fisher's exact test p = 0.011) and also with the extent of the resection (complete vs. incomplete p = 0.042). We noted no correlation between postoperative epileptiform activity and location of the resection (temporal vs. extratemporal), presence of spikes in immediate postoperative EcoG, or occurrence of auras only at 6-month follow-up.