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.     

Neuronal Complexity Loss in Interictal EEG Recorded with Foramen Ovale Electrodes Predicts Side of Primary Epileptogenic Area in Temporal Lobe Epilepsy: A Replication Study

Summary: Purpose: To investigate whether a correct lateralization of the primary epileptogenic area by means of neuronal complexity loss analysis can be obtained from interictal EEG recordings using semi-invasive foramen ovale electrodes. In a previous study with recordings from intrahippocampal depth and subdural strip electrodes it was shown that the dynamics of the primary epileptogenic area can be characterized by an increased loss of neuronal complexity in patients with unilateral temporal lobe epilepsy (TLE).
Methods: Neuronal complexity loss analysis was applied. This analysis method is derived from the theory of nonlinear dynamics and provides a topological diagnosis even in cases where no actual seizure activity can be recorded. We examined interictal EEG recorded intracranially from multipolar foramen ovale electrodes in 19 patients with unilateral TLE undergoing presurgical evaluation.
Results: The primary epileptogenic area was correctly lateralized in 16 of the 19 investigated patients. The misclassification of the side of seizure onset in three patients might be attributed to the larger distance between the foramen ovale electrodes and the mesial temporal structures as compared to intrahippocampal depth electrodes.
Conclusions: Our results confirm the previous findings and provide further evidence for the usefulness of nonlinear time-series analysis for the characterization of the spatiotemporal dynamics of the primary epileptogenic area in mesial temporal lobe epilepsy.     

An operated case of medial temporal lobe epilepsy associated with schizencephaly]

A 24-year-old male of medial temporal lobe epilepsy associated with schizencephaly was presented. He developed complex partial seizure after head trauma at the age of a year and 7 months, which became intractable at the age of 13 year. MRI demonstrated a schizencephalic cleft in the right peri-Rolandic area, cortical dysplasia in the right medical parietal and occipital lobes, and right hippocampal atrophy. Scalp-recorded EEG failed to localize the ictal onset zone. Interictal FDG-PET and ECD-SPECT indicated hypometabolism and hypoperfusion of the right entire temporal lobe, and ictal ECD-SPECT increased perfusion of this area. Chronic subdural electrode recording clearly demonstrated that ictal onset zone was located not on the schizencephalic cleft or its surrounding cortex but on the right medial temporal lobe. Following right anterior temporal lobectomy with hipppocampectomy, seizure control became easy. For the identification of the epileptogenic zone in patients with schizencephaly, chronic subdural electrode recording is mandatory.     

Subtemporal hippocampectomy preserving the basal temporal language area for intractable mesial temporal lobe epilepsy: preliminary results

PURPOSE: Decline in verbal memory as a surgical complication remains an unresolved problem in mesial temporal lobe epilepsy. Some areas in the temporal lobe associated with the language function, often including the basal temporal language area, have been removed or transected by conventional surgical procedures. The authors defined the basal temporal language area and removed only the epileptogenic zone with a subtemporal approach. METHODS: The basal temporal language area was evaluated by using long-term subdural electrodes in five patients with language-dominant-side mesial temporal lobe epilepsy. While preserving this area, the hippocampus and the parahippocampal gyrus were removed by using a combined subtemporal, transventricular, transchoroidal fissure approach. Verbal memory performance was assessed with the Wechsler Memory Scale-Revised (WMS-R) before and after the operation. RESULTS: The basal temporal language area, defined as a part of the inferior temporal gyrus, the fusiform gyrus, and the parahippocampal gyrus, was spared by entering the temporal horn via collateral sulcus. Verbal memory was significantly improved by 3 months and 1 year after the operation. CONCLUSIONS: In language-dominant-side mesial temporal lobe epilepsy, preserving the basal temporal language area would have potential to improve verbal memory outcomes after removal of the epileptogenic zone.     

皮层脑电监测下颞叶病变合并癫的手术治疗

目的探讨皮层脑电监测下合并颞叶病变的癫手术治疗效果。方法 21例伴有癫症状的颞叶病变患者,术中通过皮层脑电图确定癫灶,切除病变后,切除或热灼可疑癫疒间灶。术后随访患者的癫发作情况。结果 21例患者切除颞叶病变前均可通过皮层脑电图探及疒间波,病变及疒间灶完全切除后,癫波消失者19例,2例功能区患者虽多次皮层热灼,仍可见偶发棘波。术后20例未再有癫疒间发作,1例有部分性发作,用抗癫疒间药可控制。结论术中皮层脑电监测切除或热灼癫灶是一种有效控制颞叶病变切除术后癫发作的方法。     

颞叶癫痫手术时的皮质脑电描记

报告1980年10月至1992年6月间,在皮质脑电描记下手术治疗颞叶癫痫55例,前颞叶切除50例.杏仁核海马切除5例。皮质脑电描记结果说明颞叶癫痫的痫灶绝大多数来源于颞叶外侧皮质和颞叶内侧结构。术中皮质脑电描记可提供痫灶的精确部位和范围。     

Interictal and ictal activity recorded with subdural electrodes during preoperative evaluation for surgical treatment of epilepsy

A total of 94 subdural strip electrodes were implanted in 22 patients during preoperative EEG evaluation for surgery of epilepsy. Eighteen patients had temporal lobe seizure onset, three had frontal lobe seizure onset, and one had occipital lobe seizure onset. Most electrodes (total, 83) were localized over the temporal lobe cortex, but in four cases additional strip electrodes (total, 11) covered the frontal, parietal, and occipital lobe cortexes. The electrodes were left in place for up to 28 days. No complications occurred. Interictally, focal spiking was recorded subtemporally, mostly without being seen in electrodes recording from the lateral temporal cortex. In three patients studied with simultaneous subdural and sphenoidal wire electrodes, spiking recorded from subdural electrodes was often not seen in the sphenoidal recording. There were 151 seizures recorded (with or without simultaneous video monitoring). The mean number of seizures per patient was 6.7 (range, 0–21). The seizures were classified as having focal (80 seizures) or local (71 seizures) onset. It is concluded that subdural electrodes are safe and have a sufficient selectivity with regard to localization of interictal spiking and seizure onset in patients with mesial temporal epileptic lesions. In such cases, electrodes have to be placed subtemporally. Other cortical areas may also be explored with these electrodes.     

Feasibility and limitations of magnetoencephalographic detection of epileptic discharges: simultaneous recording of magnetic fields and electrocorticography

Magnetoencephalography (MEG) is considered clinically useful in localizing the epileptogenic focus in partial epilepsy. However, the relationship between the extent of the brain involved in paroxysmal activities and the magnetic field changes at the scalp has not been fully clarified. Furthermore, whether paroxysmal activities generated in deep brain structures such as the hippocampus can be detected magnetically is uncertain. Eight patients with temporal lobe epilepsy and two with extratemporal lobe epilepsy underwent chronic recording from subdural electrodes. Magnetic and electrocorticographic discharges representing epileptic activity were recorded simultaneously. MEG recorded magnetic field changes originating from paroxysmal activity in the superiolateral cerebral cortex when the amplitudes of the electrical paroxysmal activities exceeded 100 microV and extended over more than 3 cm2 of cortical surface. MEG failed to record paroxysmal activity localized to the medial temporal lobe. MEG is often useful in identifying a spike focus in the superiolateral aspects of the cerebral hemisphere, but not discharges arising from the medial temporal lobe. Rapid decay of the magnetic field is likely to be the reason for this limited sensitivity to medial discharges.     

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。     

Surgical technique for the insertion of grids and strips for invasive monitoring in children with intractable epilepsy

Despite improved imaging, and electrical and magnetic external mapping, there are a large number of children with intractable epilepsy in whom a focus cannot be defined by non-invasive techniques. Invasive monitoring with depth electrodes, electrode grids and/or strips is required in up to 50% of children with a suspected focal seizure disorder. In children with suspected temporal lobe epilepsy the invasive techniques are required to identify which temporal lobe is the primary focus, to separate temporal from frontal foci, and to define the extent of involvement of the lateral temporal cortex. In children and infants with non-temporal epilepsy, invasive monitoring is required to define the epileptogenic zone and to map areas of cortical specialization. The current techniques used for surgical implantation are described here. In a correctly selected population invasive monitoring will define the epileptogenic focus or foci in 90% of children; 80% will have surgically treatable epilepsy. Infection rates are less than 1% for subdural strips and 6% for grids. In 88 cases no incidence of meningitis occurred.     

Temporal lobe epilepsy associated with cystic lesion in the temporal lobe and middle cranial fossa]

Four patients out of 52 patients with temporal lobe epilepsy (TLE), who underwent epilepsy surgery in our hospital since September of 1994, had cystic lesions in the temporal lobe and middle cranial fossa. Case 1 had old hematoma cavity in the inferior temporal gyrus and chronic subdural electrode recording revealed the ictal onset zone to be localized in the ipsilateral medial temporal region. Case 2 had cystic ganglioglioma in the temporal tip, and intraoperative electrocorticography demonstrated independent paroxysmal activities from medial temporal region and temporal tip near the cyst. Both area were resected and the patients became seizure free. Case 3 and 4 had arachnoid cysts in the middle cranial fossa. Chronic subdural electrode recording revealed that the ictal onset zone was localized in the ipsilateral inferior temporal gyrus (that had microdysgenesis) in Case 3 and contralateral medial temporal region (that had hippocampal sclerosis) in Case 4, respectively. These finding suggest that co-existence of extra-axial cyst such as Case 3 and 4 is incidental and that arachnoid cyst is less epileptogenic. However, intra-axial cyst such as Case 1 and 2 is epileptogenic and complicated physiological mechanism such as kindling phenomenon or secondary epileptogenesis may effect on the hippocampus. Comprehensive presurgical evaluation including electrocorticography is needed in the surgical treatment of TLE with cystic lesion.     

Language cortex representation: Effects of developmental versus acquired pathology

Relatively little is known about language cortex representation in patients with developmental pathology and epilepsy. We report the results of mapping language by electrical stimulation of chronically implanted subdural electrodes in 34 patients (mean age, 12.2 years) evaluated for epilepsy surgery, 28 of whom had magnetic resonance imaging or histological evidence of developmental tumors or cortical dysplasia. Language cortex was identified in the temporal or frontal lobe of 19 patients (left hemisphere in 17, right hemisphere in 2), and overlapped or bordered the epileptogenic region in 12. Language cortex was not found in the frontal or temporal lobe of 15 patients (left hemisphere in 4, right hemisphere in 11) and was presumed to be contralateral to grid placement. Three patients with left-hemisphere perinatal or postnatal cerebral insults before the age of 5 years had no language in the left hemisphere, while 3 patients with insults between the ages of 6 and 16 years had preserved left-hemisphere language. Developmental lesions and early onset seizures do not displace language cortex from prenatally determined sites, whereas lesions acquired before the age of 5 years may cause language to relocate to the opposite hemisphere, but only when language cortex is destroyed.     

Lateralization of temporal lobe foci: depth versus subdural electrodes.

OBJECTIVES: Definitive localization of an epileptic focus correlates with a favorable outcome following epilepsy surgery. This study was undertaken to determine the incremental value of data yielded for surgical decision making when using subdural electrodes alone and in addition to depth electrodes for temporal lobe epilepsy. METHODS: Standardized placement for intracranial electrodes included: (1) longitudinal placement of bilateral temporal lobe depth electrodes; (2) bilateral subtemporal subdural strips; and (3) bilateral orbitofrontal subdural strips. Sixty-three events were randomly reviewed for: (1) subdural electrodes alone; and (2) depth electrodes in conjunction with subdural electrodes. RESULTS: Of the 63 seizures, 54 (85.7%) demonstrated congruent lateralization to ipsilateral subtemporal subdural strip electrodes (based on depth electrode localization) when subdural strip electrodes were utilized alone. In 3 of 22 patients, 7 seizures demonstrated 'false localization' on subdural electrode analysis alone when compared with depth recording and post-surgical outcome. For these 3 patients, retrospective review of neuroimaging demonstrated suboptimal ipsilateral placement of subtemporal subdural electrodes with the most mesial electrode lateral to the collateral sulcus. Four additional patients had suboptimal placement of subtemporal subdural electrodes. Two of these 4 patients had congruent localization with subdural electrodes to ipsilateral depth electrodes despite suboptimal placement. Subtemporal subdural electrodes accurately localized for all seizures from the mesial temporal lobe when the mesial electrodes of the subtemporal subdural strip recorded mesial to the collateral sulcus from the parahippocampal region. CONCLUSION: We conclude that although there are high concordance rates between subdural and depth electrodes, localization of seizure onset based on subdural strip electrodes alone may result in inaccurate focus identification with potential for possible suboptimal treatment of temporal lobe epilepsy. When subtemporal subdural electrodes provide recording from the parahippocampal region, there is accurate localization of the seizure focus. If suboptimal placement occurs lateral to the collateral sulcus, the electroencephalographer cannot make a definitive identification of the seizure focus.     

Two magneto-encephalographic epileptic foci did not coincide with the electrocorticographic ictal onset zone in a patient with temporal lobe epilepsy.

To evaluate the usefulness and limitations of magneto-encephalography (MEG) for epilepsy surgery, we compared 'interictal' epileptic spike fields on MEG with ictal electrocorticography (ECoG) using invasive chronic subdural electrodes in a patient with intractable medial temporal lobe epilepsy (MTLE) associated with vitamin K deficiency intracerebral hemorrhage. A 19-year-old male with an 8-year history of refractory complex partial seizures, secondarily generalized, and right hemispheric atrophy and porencephaly in the right frontal lobe on MRI, was studied with MEG to define the interictal paroxysmal sources based on the single-dipole model. This was followed by invasive ECoG monitoring to delineate the epileptogenic zone. MEG demonstrated two paroxysmal foci, one each on the right lateral temporal and frontal lobes. Ictal ECoG recordings revealed an ictal onset zone on the right medial temporal lobe, which was different from that defined by MEG. Anterior temporal lobectomy with hippocampectomy was performed and the patient has been seizure free for two years. Our results indicate that interictal MEG does not always define the epileptogenic zone in patients with MTLE.     

Surgical resection for intractable epilepsy in "double cortex" syndrome yields inadequate results

PURPOSE: To analyze the results of surgical treatment of intractable epilepsy in patients with subcortical band heterotopia, or double cortex syndrome, a diffuse neuronal migration disorder. METHODS: We studied eight patients (five women) with double cortex syndrome and intractable epilepsy. All had a comprehensive presurgical evaluation including prolonged video-EEG recordings and magnetic resonance imaging (MRI). RESULTS: All patients had partial seizures, with secondary generalization in six of them. Neurologic examination was normal in all. Three were of normal intelligence, and five were mildly retarded. Six patients underwent invasive EEG recordings, three of them with subdural grids and three with stereotactic implanted depth electrodes (SEEG). Although EEG recordings showed multilobar epileptic abnormalities in most patients, regional or focal seizure onset was recorded in all. MRI showed bilateral subcortical band heterotopia, asymmetric in thickness in three. An additional area of cortical thickening in the left frontal lobe was found in one patient. Surgical procedures included multiple subpial transections in two patients, frontal lesionectomy in one, temporal lobectomy with amygdalohippocampectomy in five, and an additional anterior callosotomy in one. Five patients had no significant improvement, two had some improvement, and one was greatly improved. CONCLUSION: Our results do not support focal surgical removal of epileptogenic tissue in patients with double cortex syndrome, even in the presence of a relatively localized epileptogenic area.     

Basal Temporal Subdural Electrodes in the Evaluation of Patients with Intractable Epilepsy

In evaluation of patients with complex partial seizures who are candidates for surgical treatment, exact definition of the epileptogenic focus is essential for a good surgical outcome. We report a new technique which permits detailed mapping of the epileptogenic activity in the basal temporal lobe and the convexity of the temporal lobe. The technique consists of placement of at least 16 basal temporal electrodes and an additional 64 electrodes covering the temporal convexity. This extensive coverage permits accurate definition of the limits of the epileptogenic focus and also of adjacent functional areas and therefore allows more significant determination than have previous techniques of the ideal extent of the surgical resection. This accuracy cannot be achieved with depth electrodes or the limited coverage provided by previously reported epidural or subdural electrode techniques.     

Revisiting the role of the insula in refractory partial epilepsy

Purpose:   Recent evidence suggesting that some epilepsy surgery failures could be related to unrecognized insular epilepsy have led us to lower our threshold to sample the insula with intracerebral electrodes. In this study, we report our experience resulting from this change in strategy.
Methods:   During the period extending from October 2004 to June 2007, 18 patients had an intracranial study including 10 with insular coverage. The decision to sample the insula with intracerebral electrodes was made in the context of (1) nonlesional parietal lobe-like epilepsy; (2) nonlesional frontal lobe-like epilepsy; (3) nonlesional temporal lobe-like epilepsy; and (4) atypical temporal lobe-like epilepsy.
Results:   Intracerebral recordings confirmed the presence of insular lobe seizures in four patients. Cortical stimulation performed in 9 of 10 patients with insular electrodes elicited, in decreasing order of frequency, somatosensory, viscerosensory, motor, auditory, vestibular, and speech symptoms.
Discussion:   Our results suggest that insular cortex epilepsy may mimic temporal, frontal, and parietal lobe epilepsies and that a nonnegligeable proportion of surgical candidates with drug-resistant epilepsy have an epileptogenic zone that involves the insula.     

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.     

颞叶癫痫语言皮层的功能性MR定位研究

目的： 采用功能性ＭＲ对颞叶癫痫患者语言皮层定位, 为研究颞叶癫痫患者语言功能及手术治疗顽固性颞叶癫痫提供新的定位手段; 方法： 对８ 例顽固性颞叶癫痫患者进行颞叶语言皮层的功能性ＭＲ扫描, 作为选择术式的参考依据; 结果： ８ 例患者均发现颞叶皮层出现信号改变, 其中６ 例位于左侧颞叶; ２ 例发现有右侧颞叶活动, ３ 例患者接受阿米妥实验, 与功能ＭＲ结果一致; 术后患者未出现语言功能障碍。结论： 采用功能性ＭＲ可为颞叶癫痫患者语言皮层活动提供可靠的术前判断。