Combined depth and subdural electrode investigation in uncontrolled epilepsy

We used both depth and subdural electrodes to obtain localization of the seizure focus in 47 medically refractory epileptic patients. Seizures were localized in 33 patients. Onset was consistently localized by the depth electrodes in 23 patients, was variable or simultaneous in depth and subdural electrodes in 6 (in the same lobe), and was consistently localized to subdural electrodes in 4. All patients localized with subdural electrodes were extratemporal and 3 of the 4 had lesions on imaging studies which helped guide location of electrode placement. Eighty-seven percent of temporal lobe seizures began in hippocampus (recorded by the depth electrode), and 80% were eventually propagated to the ipsilateral temporal neocortex (recorded by the subdural electrode). In 8 patients with bilateral temporal depth and subdural recording, seizures never spread to the contralateral neocortex before the ipsilateral neocortex. Subdural electrodes were 20% less sensitive than depth electrodes in detection of seizures beginning in hippocampus but were accurate when lateralized. Variable or simultaneous unilateral neocortical versus hippocampal temporal lobe seizure onset, determined by the combined study, was significantly correlated with less favorable seizure control after anteromedial temporal lobectomy and hippocampectomy.     

Intracranial EEG Substrates of Scalp Ictal Patterns from Temporal Lobe Foci

Summary: Purpose: To determine the intracranial EEG features responsible for producing the various ictal scalp rhythms, which we previously identified in a new EEG classification for temporal lobe seizures. Methods: In 24 patients, we analyzed simultaneous intracranial and surface ictal EEG recordings (64 total channels) obtained from a combination of intracerebral depth, subd-ural strip, and scalp electrodes. Results: Four of four patients with Type 1 scalp seizure patterns had mesial temporal seizure onsets. However, discharges confined to the hippocampus produced no scalp EEG rhythms. The regular 5- to 9-Hz subtemporal and temporal EEG pattern of Type 1a seizures required the synchronous recruitment of adjacent inferolateral temporal neocortex. Seizure discharges confined to the mesiobasal temporal cortex produced a vertex dominant rhythm (Type 1c) due to the net vertical orientation of dipolar sources located there. Ten of 13 patients with Type 2 seizures had inferolateral or lateral, temporal neocortical seizure onsets. Initial cerebral ictal activity was typically a focal or regional, low voltage, fast rhythm (20–40 Hz) that was often associated with widespread background flattening. Only an attenuation of normal rhythms was reflected in scalp electrodes. Irregular 2- to 4-Hz cortical ictal rhythms that commonly followed resulted in a comparably slow and irregular scalp EEG pattern (Type 2a). Type 2C seizures showed regional, periodic, 1– to 4-Hz sharp waves following intracranial seizure onset. Seven patients had Type 3 scalp seizures, which were characterized by diffuse slowing or attenuation of background scalp EEG activity. This resulted when seizure activity was confined to the hippocampus, when there was rapid seizure propagation to the contralateral temporal lobe, or when cortical ictal activity failed to achieve widespread synchrony. Conclusions: Type 1, 2, and 3 scalp EEG patterns of temporal lobe seizures are not a reflection of cortical activity at seizure onset. Differences in the subsequent development, propagation, and synchrony of cortical ictal discharges produce the characteristic scalp EEG rhythms.     

Lateralizing and localizing values of ictal onset recorded on the scalp: evidence from simultaneous recordings with intracranial foramen ovale electrodes

PURPOSE: The value of scalp recordings to localize and lateralize seizure onset in temporal lobe epilepsy has been assessed by comparing simultaneous scalp and intracranial foramen ovale (FO) recordings during presurgical assessment. The sensitivity of scalp recordings for detecting mesial temporal ictal onset has been compared with a "gold standard" provided by simultaneous deep intracranial FO recordings from the mesial aspect of the temporal lobe. As FO electrodes are introduced via anatomic holes, they provide a unique opportunity to record simultaneously from scalp and mesial temporal structures without disrupting the conducting properties of the brain coverings by burr holes and wounds, which can otherwise make simultaneous scalp and intracranial recordings unrepresentative of the habitual EEG. METHODS: Simultaneous FO and scalp recordings from 314 seizures have been studied in 110 patients under telemetric presurgical assessment for temporal lobe epilepsy. Seizure onset was identified on scalp records while blind to recordings from FO electrodes and vice versa. RESULTS: Bilateral onset (symmetric or asymmetric) was more commonly found in scalp than in FO recordings. The contrary was true for unilateral seizure onset. In seizures with bilateral asymmetric onset on the scalp, the topography of largest-amplitude scalp changes at onset does not have localizing or lateralizing value. However, 75-76% of seizures showing unilateral scalp onset with largest amplitude at T1/T2 or T3/T4 had mesial temporal onset. This proportion dropped to 42% among all seizures with a unilateral scalp onset at other locations. Of those seizures with unilateral onset on the scalp at T1/T2, 65.2% showed an ipsilateral mesial temporal onset, and 10.9% had scalp onset incorrectly lateralized with respect to the mesial temporal onset seen on FO recordings. In seizures with a unilateral onset on the scalp at electrodes other than T1/T2, the proportions of seizures with correctly and incorrectly lateralized mesial temporal onset were 37.5 and 4.2%, respectively. Thus the ratio between incorrectly and correctly lateralized mesial temporal onsets is largely similar for seizures with unilateral scalp onset at T1/T2 (16.7%) and for seizures with unilateral scalp onset at electrodes other than T1/T2 (11.2%). The onset of scalp changes before the onset of clinical manifestations is not associated with a lower proportion of seizures with bilateral onset on the scalp, or with a higher percentage of mesial temporal seizures or of mesial temporal seizures starting ipsilateral to the side of scalp onset. In contrast, the majority (78.4%) of mesial temporal seizures showed clinical manifestations starting after ictal onset on FO recordings. CONCLUSIONS: A bilateral scalp onset (symmetric or asymmetric) is compatible with a mesial temporal onset, and should not deter further surgical assessment. Although a unilateral scalp onset at T1/T2 or T3/T4 is associated with a higher probability of mesial temporal onset, a unilateral onset at other scalp electrodes does not exclude mesial temporal onset. A unilateral scalp onset at electrodes other than T1/T2 is less likely to be associated with mesial temporal onset, but its lateralizing value is similar to that of unilateral scalp onset at T1/T2. The presence of clinical manifestations preceding scalp onset does not reduce the localizing or lateralizing values of scalp recordings.     

Electroclinical analysis of postictal noserubbing

BACKGROUND: Postictal noserubbing (PIN) has been identified as a good, albeit imperfect, lateralizing and localizing sign in human partial epilepsy, possibly related to ictal autonomic activation. METHODS: PIN was studied prospectively in a group of consecutive patients admitted for video-EEG monitoring, with the laterality of noserubbing correlated with electrographic sites of seizure onset, intra- and interhemispheric spread, and sites of seizure termination. RESULTS: PIN was significantly more frequent in temporal than extratemporal epilepsy (p<0.001; 23/41 (56%) patients and 41/197 (21%) seizures in temporal lobe epilepsy compared with 4/34 (12%) patients and 12/167 (7%) seizures in extratemporal epilepsy). The hand used to rub the nose was ipsilateral to the side of seizure onset in 83% of both temporal and extratemporal seizures. Seizures with contralateral PIN correlated with spread to the contralateral temporal lobe on scalp EEG (p<0.04). All extratemporal seizures with PIN showed spread to temporal lobe structures. One patient investigated with intracranial electrodes showed PIN only when ictal activity spread to involve the amygdala: seizures confined to the hippocampus were not associated with PIN. PIN was not observed in 63 nonepileptic events in 17 patients. Unexpectedly, one patient with primary generalized epilepsy showed typical PIN after 1/3 recorded absence seizures. CONCLUSIONS: This study confirms PIN as a good indicator of ipsilateral temporal lobe seizure onset. Instances of false lateralization and localization appear to reflect seizure spread to contralateral or ipsilateral temporal lobe structures, respectively. Involvement of the amygdala appears to be of prime importance for induction of PIN.     

颞叶癫痫的痫性放电传导和临床症状的颅内电极脑电图研究

目的 探讨颞叶癫痫患者痫性放电的传导部位、时间和相应的临床症状变化.方法 对2003年6月至2007年5月确诊为颞叶癫痫并行颅内电极埋置检查的48例患者的颅内电极脑电图和发作期症状进行回顾性分析,通过在双侧海马放置的针状电极和颢叶、额叶等放置的条状皮层电极,找出发作起源部位、早期传导部位、传导时间及发作起始症状和传导后症状.结果 共记录126次临床癫痫发作,105次记录到传导部位,其中同侧颢叶内传导22次,额叶39次,顶枕叶18次,对侧海马10次,16次全脑放电.44.8%传导时间小于2.5 s,55.2%传导时间超过2.5 s,且有17.1%超过5 s.101次发作中出现初始症状,其中82.2%为意识水平下降、自动症、恐惧等;99次记录到传导后新症状,其中出现颞叶外传导者82.2%出现抽动或强直表现.结论 颞叶癫痫放电传导部位主要是同侧的额叶与颞叶内部,但也可直接到对侧海马结构,临床症状与传导位置有关,传导速度多较慢.     

Sensitivity of recordings at sphenoidal electrode site for detecting seizure onset: evidence from scalp, superficial and deep foramen ovale recordings.

OBJECTIVES: Some authors have recently stressed that the position of the tip of sphenoidal electrodes plays a crucial role in their efficacy in detecting ictal onset. An opportunity to test this hypothesis is provided by recordings from the most superficial contacts of foramen ovale (FO) electrode bundles because these contacts are located at the FO, in a position equivalent to that of optimally located sphenoidal electrodes. To simplify wording, recordings obtained by superficial FO electrodes will hereafter be called sphenoidal recordings, although they have not been obtained with standard sphenoidal electrodes. The sensitivities of simultaneous scalp and sphenoidal recordings for detecting ictal onset have been compared with each other, and with a 'gold standard' provided by simultaneous deep intracranial FO recordings from the mesial aspect of the temporal lobe. METHODS: Three hundred and fourteen seizures obtained from 110 patients under telemetric presurgical assessment for temporal lobe epilepsy have been studied. Scalp electrodes included anterior temporal placements. All scalp electrodes were considered when identifying seizure onset but the anterior temporal electrodes were most frequently involved. RESULTS: Ictal onset time at sphenoidal and scalp recordings: initial ictal changes appeared simultaneously in scalp and sphenoidal recordings in 123 seizures (39.2%). Initial changes occurred earlier in sphenoidal recordings in 63 seizures (20.1%), whereas they were seen earlier on the scalp in 76 seizures (24.2%). Artefacts prevented the comparison between sphenoidal and scalp recordings in 16 seizures (5.1%) and no ictal changes were seen on the scalp and/or sphenoidal recordings in 36 seizures (11.5%). In most of the 63 seizures where ictal changes appeared earlier in sphenoidal recordings, a delayed ipsilateral scalp onset was seen as the signal amplitude increased or scalp changes could be identified retrospectively on the scalp with an onset which appeared simultaneous and ipsilateral to the initial sphenoidal changes. Sphenoidal recordings supplied additional information when compared to scalp recordings in only 22 seizures (7%): in 5 seizures with artefacts on the scalp, in 6 seizures with no changes on the scalp and in 11 seizures with discrepant laterality at onset. Congruence in laterality with respect to deep intracraneal FO recordings: of the 61 seizures with unilateral onset on the scalp, onsets at sphenoidal recordings and deep FO electrodes were ipsilateral in most cases. In only 3 of these 61 seizures (4.9%), sphenoidal recordings lateralized ipsilateral to the deep FO electrodes in the presence of a contralateral onset on the scalp. In 14 among the 122 seizures (11.5%) with bilateral asymmetrical onset on the scalp, sphenoidal recordings lateralized seizure onset ipsilateral to the deep FO electrodes in the presence of a contralateral scalp onset. Thus, when compared with scalp EEG, sphenoidal recordings increased laterality congruence with respect to deep FO electrodes in 17 seizures (5.4%). CONCLUSIONS: Extracranial electrodes located next to the FO at the sphenoidal electrode site yield an improvement over suitable surface electrodes in the identification of ictal onset in only 5.4-7% of seizures. Such improvement derives from the fact that the low amplitude signals often seen at seizure onset may show higher amplitude on sphenoidal than on scalp recordings.     

Hippocampal N-acetylaspartate in neocortical epilepsy and mesial temporal lobe epilepsy

Previous magnetic resonance spectroscopy (MRS) studies have shown that N?acetylaspartate (NAA) is reduced not only in the ipsilateral but also in the contralateral hippocampus of many patients with mesial temporal lobe epilepsy (mTLE). The reason for the contralateral damage is not clear. To test whether the hippocampus is also damaged if the focus is outside the hippocampus, we have measured patients with neocortical epilepsy (NE). Therefore, the goals of this study were to determine if hippocampal NAA is reduced in NE and if hippocampal NAA discriminates NE from mTLE. MRS imaging (MRSI) studies were performed on 10 NE patients and compared with MRSI results in 23 unilateral mTLE patients and 16 controls. The results show that, in contrast to mTLE, NAA was not reduced in the hippocampus of NE patients, neither ipsilateral nor contralateral to the seizure focus. These results suggest that repeated seizures do not cause secondary damage to the hippocampus. The absence of spectroscopic differences in NE may help to distinguish NE from mTLE.     

Ictal Contralateral Paresis in Complex Partial Seizures

Summary: Certain behaviors that occur during a complex partial seizure (CPS) are useful in lateralizing the side of seizure onset. In 5 (5.3%) of 94 consecutive patients with partial epilepsy, we observed ictal unilateral arm and hand paresis during 27 of 34 CPS. In all these seizures, this behavior occurred contralateral to an epileptogenic temporal lobe, as determined by video-EEG monitoring and surgical outcome. In 5 of the 27 seizures, an observer demonstrated that the paretic arm and hand were flaccid. None of these patients had postictal (Todd's) paralysis. In most of the seizures, the arm ipsilateral to seizure onset had simultaneous purposeful movements or automatisms, sometimes with awkward posturing. Ictal unilateral paresis is distinctly different from ictal dystonia or postictal paralysis and consistently lateralizes seizure onset to the contralateral temporal lobe. Recognition of this particular ictal behavior and comparison to other simultaneous behaviors can aid in the lateralization and possibly localization of the epileptogenic zone.     

Unilateral hippocampal sclerosis with contralateral temporal scalp ictal onset

PURPOSE: To investigate the clinical characteristics and surgical outcomes in patients with unilateral hippocampal sclerosis whose scalp ictal EEG recordings localize to the opposite temporal lobe. METHODS: We retrospectively reviewed the data of all adult patients who had undergone depth electrode implantation for suspected temporal lobe epilepsy (TLE) at UCLA (1993-2000) or the Montreal Neurological Institute (1991-1998) to identify patients who had (a) unilateral hippocampal atrophy, and (b) surface ictal recordings in which the majority of seizures appeared to initiate in the opposite temporal lobe, with few or none that were concordant with the hippocampal atrophy. RESULTS: Of 109 patients with suspected TLE who underwent depth electrode study at the two centers, five patients met the aforementioned criteria. Four of these five had very severe hippocampal atrophy, whereas the fifth had mild atrophy but extensive signal change on magnetic resonance imaging (MRI). Depth electrode recordings in four of the five patients yielded clear ictal onset in the mesial temporal lobe ipsilateral to the imaging abnormality (contralateral to apparent scalp ictal onset). One patient had an unusual bitemporal onset pattern, which was nonetheless suggestive of onset in the sclerotic hippocampus. No patient had intracranial ictal onset contralateral to the imaging abnormality. All patients underwent resection of the structurally abnormal temporal lobe. After follow-up of > or = 2 years, four (80%) of five patients were seizure free, while the fifth showed lesser improvement (class III). CONCLUSIONS: Some patients with severe hippocampal sclerosis (sometimes called a "burned-out hippocampus") have atypical spread of ictal discharges, resulting in apparent gross discordance between imaging and scalp ictal recordings. These patients nonetheless have excellent surgical outcomes on the whole. Whether such patients may forego intracranial recordings requires further study.     

Contralateral motor automatisms in neocortical temporal lobe epilepsy

BACKGROUND: The lateralizing value of the motor automatisms is generally doubted in most patients with temporal lobe epilepsy. However, subgroup analysis of the seizures of temporal lobe origin suggests a role for motor automatisms in discriminating seizures of neocortical versus mesial temporal lobe origin. METHODS: Video-EEG of a patient with well-defined neocortical temporal lobe epilepsy was reviewed to assess the localizing value of motor automatisms. RESULTS: We report a patient with left upper extremity motor automatisms and clonic movements of the proximal left lower extremity with altered awareness as the sole manifestations of right temporal neocortical seizures. CONCLUSION: Early onset unilateral motor automatisms without dystonic posturing can localize the seizure origin to the contralateral temporal lobe neocortex.