Intracranial EEG with Very Low Frequency Activity Fails to Demonstrate an Advantage Over Conventional Recordings

PURPOSE: Conventional scalp and intracranial EEG is recorded within a limited band of frequencies (0.3-70 Hz) based on the premise that clinically relevant cerebral activity occurs within this frequency range. Ikeda et al. recently demonstrated focal very low frequency activity (VLFA), <0.3 Hz, at seizure onset for both intra- and extracranial recordings. The purpose of this investigation was prospectively to study VLFA during seizures in intracranial recordings to determine whether activity in this frequency range provides useful information regarding localization of seizure onset and spread. METHODS: Patients undergoing intracranial electrode implantation were studied by using a high-pass filter of 0.01 Hz. The timing, location, and pattern of seizure onset were first determined by using a digital high-pass filter of 0.3 Hz (conventional seizure onset). Seizures were then reviewed without digital filters and the presence of VLFA recorded, along with its timing and location. RESULTS: Forty-seven seizures were recorded in four patients. VLFA was not observed in 29 seizures and, in one other case, VLFA occurred simultaneous with movement. Of seizures with VLFA (n = 17), the timing and location of VLFA were not consistent with those of conventional seizure onset or propagation. CONCLUSIONS: Our study failed to demonstrate any clinical advantage of intracranial telemetry recordings with a high-pass filter of 0.01 Hz over conventional recordings with regard to determining the timing and location of seizure onset and propagation.     

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.     

Generalized absence seizures with 10-15 Hz fast discharges.

OBJECTIVE: To report clinical and EEG features in 5 adults with unusual, fast rhythmic discharges accompanying absence seizures. DESIGN AND METHODS: The 5 patients presented with uncontrolled seizures. All had EEG-video monitoring with recorded seizures. Video seizures were reviewed and ictal as well as interictal epileptiform activity was analyzed. The patients were followed up after appropriate therapy for a minimum of 6 months. RESULTS: There were 3 women and two men, with a mean age of 37 years (range: 23-59). Two patients had onset of absence seizures in childhood, one in adolescence and two after age 20. All patients also had generalized tonic-clonic seizures. Ictal EEG recordings showed generalized spike and wave (SW) discharges of variable dominant frequencies (2.5-6 Hz) and intermingled 10-15 Hz generalized rhythmic discharges which also occurred in isolation or as the dominant activity. Interictal recordings showed similar but shorter 2.5-6 Hz generalized SW discharges. The background activity was normal in 3 patients and mildly slow in two who had very frequent absence seizures during the recording period. Four patients became seizure free and one had 75% improvement on appropriate antiabsence therapy. CONCLUSIONS: The fast 10-15 Hz rhythmic discharges that we report appear to occur mostly in adult patients with absence, as well as, generalized tonic-clonic seizures. They can occur in isolation or be embedded in more typical SW discharges accompanying typical absence seizures. Their presence does not imply a poor prognosis for seizure control.     

Absence seizures with evolution into generalized tonic-clonic activity: clinical and EEG features

PURPOSE: To report the clinical and electrographic features of absence seizures evolving into generalized tonic-clonic (GTC) activity in six patients with idiopathic generalized epilepsy. METHODS: All patients were referred for evaluation of refractory seizures and underwent video-EEG monitoring after discontinuation of their antiepileptic drugs (AEDs). We analyzed the video-EEG recordings for seizure semiology as well as ictal and interictal activity. We also reviewed the initial clinical data in all patients. RESULTS: All patients were women, with a mean age of 27 years (range, 14-43 years). The mean age at seizure onset was 12 years (range, 5-15 years). Family history was positive for epilepsy in four patients. All patients had recorded seizures with an onset that was characteristic of generalized absence clinically and electrographically, with evolution into GTC activity. The EEG onset was with generalized 2.5-to 5-Hz spike-and-wave discharges, with evolution into faster rhythmic activity. Interictal EEG recordings showed generalized 2-to 5-Hz spike-and-wave discharges. All had normal background activity. All patients were treated with divalproex monotherapy. Five patients have been seizure free, and one had a single breakthrough GTC seizure during a follow-up period of 12-36 months. CONCLUSIONS: GTC activity may evolve from typical absence seizures. This seizure type should be included in the International Classification of Seizures. Its recognition and distinction from complex partial seizures with secondary generalization are important for appropriate therapy.     

Interictal indices of temporal seizure origin

Two studies assessed the value of temporal lobe interictal electroencephalographic (EEG) spikes and delta in indicating side of temporal epileptogenesis. The first study determined laterality of spikes/delta in awake recordings of 56 patients whose seizures all began unilaterally as proven by (1) EEG-recorded seizures and (2) >90% improvement after lobectomy. Spikes of 52 (93%) and delta of 46 (82%) patients predominated or appeared exclusively ipsilateral to seizure origin. Neither predominated contralaterally in any patient. The second study investigated laterality of temporal seizures in a separate group of 156 patients with various side vs side spike or delta ratios on 1 to ≥4 awake recordings. Ninety-nine of 104 patients (95%) with temporal spikes on four or more awake recordings had most or all seizures ipsilateral to most spikes, including 79 of 80 (99%) of those with ≥3 side vs side spike ratios. Among the 120 patients with high (≥3) side vs side spike ratios, most or all seizures of 118 (98%) originated ipsilateral to most spikes. Predominant seizure origin also correlated with lateralized arrhythmic delta—from 90% ipsilateral seizures of those with one EEG with delta to 100% with ≥4 such EEGs. Data from these two studies using opposite directions of analysis (seizures ← spikes/delta and spikes/delta → seizures) demonstrate high correlations between laterality of interictal and ictal entities, particularly if temporal spikes clearly predominate on one side and if unilateral temporal delta activity persists over several recordings. Such correlations suggest that the awake interictal scalp EEG cannot be ignored when assessing laterality of temporal epileptogenesis.     

Seizure suppression by adenosine-releasing cells is independent of seizure frequency

PURPOSE: Intraventricular cellular delivery of adenosine was recently shown to be transiently efficient in the suppression of seizure activity in the rat kindling model of epilepsy. We tested whether the suppression of seizures by adenosine-releasing grafts was independent of seizure frequency. METHODS: Adenosine-releasing cells were encapsulated and grafted into the lateral brain ventricle of rats kindled in the hippocampus. During 4 weeks after grafting, electric test stimulations were delivered at a frequency of either once a week or 3 times per week. Seizure activity was evaluated by visual scoring of seizure severity and by the recording of EEGs. RESULTS: Adenosine released from encapsulated cells exerted potent antiepileptic activity for >/=2 weeks. One week after grafting, treated rats displayed a complete protection from clonic seizures, and a protection from focal seizures was observed in the majority of animals. Seizure suppression was accompanied by a reduction of afterdischarges in EEG recordings. The protective efficacy of the grafted cells was the same irrespective of whether electrical test stimulations were delivered 1 or 3 times per week. Rats receiving control grafts continued to display full clonic convulsions. CONCLUSIONS: This study demonstrated that the frequency of test stimulations did not influence the seizure-suppressive potential of adenosine-releasing grafts. Thus the local delivery of adenosine is likely to be effective in seizure control over a threefold range of seizure-discharge frequency.     

红藻氨酸诱导大鼠癫痫发作的电生理机制研究

目的　探讨红藻氨酸 ( KA)诱导大鼠复杂部分性癫痫发作的 EEG特点以及可能的电生理起搏点位置。方法　在立体定位指引下 ,将 EEG记录电极植入 1 2只大鼠双侧海马、额叶皮质或杏仁核中 ,其中 8只为实验组 ,4只为对照组。手术后 1周在大鼠清醒状态下 ,连续描记 KA或盐水注射后 EEG 1 2 0 min,观察 EEG波形、波幅以及频率的变化特点并记录每次电发作的起搏点位置。结果　 ( 1 ) KA注射后大鼠 EEG表现出多种形式的放电波形 ,典型波形有单棘波、多棘波、多相棘波、正相棘波、棘节律、节律性慢波、棘慢波等。 ( 2 )大鼠在凝视发作以及自动症发作时海马、杏仁核和额叶皮质均有异常放电。 ( 3) KA注射后大鼠电发作起搏点不固定。 ( 4 )各导放电频率多数情况下一致 ,偶有不一致现象。 ( 5 )存在亚临床放电。结论　 ( 1 ) KA注射后大鼠 EEG表现为多种形式的电发作活动 ;( 2 )大鼠在复杂部分性发作过程中不仅有边缘系统参与 ,也有边缘外额叶皮质参与 ;( 3)KA模型中 ,电发作起搏点不固定 ,KA注射后大鼠脑内可能存在一个异常的神经元网络 ,在网络中存在放电不均衡现象。     

Electrocorticographical observation of seizures induced by pentylenetetrazol (PTZ) injection in rats

The various seizure responses observed behaviorally in freely moving rats after repeated pentylenetetrazol (PTZ) injections were compared with simultaneous electrocorticographical (ECoG) recordings. Seizures induced were divided into 7 behavioral categories (grade 0-6): grade 0, no behavioral seizures; grade 1, head nodding, head twitching; grade 2, myoclonic jerks; grade 3, head twisting, forelimb clonic convulsions; grade 4, kangaroo position; grade 5, falling down; grade 6, tonic convulsions. Specific behavioral seizure types were always associated with identifiable ECoG patterns. All rats which exhibited higher than grade 3 seizures developed decrease in spontaneous movements and decreased amplitude in ECoG activity after the end of their behavioral seizures, which suggests the existence of post-ictal inhibition. Both myoclonic jerks (grade 2) and tonic convulsions (grade 6) are important features of these seizure types which are not seen in electrical amygdaloid seizure models. This seizure classification will be useful for further rat PTZ seizure studies.     

Electroencephalographic findings in children with cerebral palsy: a study of 151 patients

EEG abnormalities were studied in 151 patients (79 boys, 72 girls age range 0.4-13 years) with cerebral palsy (CP). They all had standardised EEG recordings, which were read by the same electroencephalographer. Eighty-one children had seizures and 70 were seizure-free. The EEG abnormalities in the seizure group included slow waves in 36 patients (generalised asynchronous in 33 and generalised synchronous in 3); amplitude abnormalities in 2 (focal in 1, generalised 1); epileptiform activity (including isolated sharp waves, isolated spikes, and spike-wave and polyspike-wave complexes) was seen in 66 (focal in 12; generalised in 48 and multifocal in 6). Hypsarrythmia was found in 4 and burst suppression in 1. Only 6 recordings were normal giving an overall percentage of abnormality of 92.6%. Of the CP patients without seizures, 28 (40%) showed generalised asynchronous slow waves; epileptiform activity was found in 27 (focal in 2, generalised in 23 and multifocal in 2); 3 subjects showed hypsarrythmia and 24 recordings were normal. The overall percentage of abnormality in this group was 76%. Cerebral palsy in children, regardless of its cause may be associated with generalised focal EEG abnormalities. This may reflect heterogeneity of the neural-generator in the underlying disease process.     

Dysplastic Cerebellar Epilepsy: Complete Seizure Control Following Resection of a Ganglioglioma

Subcortical epilepsy has been a controversial issue, partially settled by evidence showing seizure generation in hypothalamic hamartomas and also by reports of seizures caused by cerebellar lesions. We report 4-year-old girl with right hemifacial seizures and autonomic phenomena, in whom MRI showed an irregular mass in the right cerebellar peduncle. Despite several unremarkable video-EEG recordings, seizure origin in the lesion was hypothesized. Complete resection was feasible, histopathology showed a ganglioglioma, and she has been seizure free for 3 years. A fine line separates these developmental tumors from focal cortical dysplasia, and the homogeneous presentation of this entity led us to propose the terminology dysplastic cerebellar epilepsy.     

热性惊厥持续状态复发的危险因素分析

目的 探讨儿童热性惊厥持续状态(FSE)复发的危险因素.方法 收集138例FSE患儿的临床资料,并于出院后进行2个月至8.3年的随访.根据随访结果,将患儿分为热性惊厥复发组、癫痫进展组及无惊厥复发组,分析FSE复发的相关因素.结果 根据随访结果,热性惊厥复发30例(21.7％)(热性惊厥复发组),8例(5.8％)进展为...     

Automatic seizure detection: improvements and evaluation.

Improvements to an existing automatic seizure detection program are described. They are aimed at taking into account a larger temporal context and thus improving the specificity of the detections. Results were evaluated on 293 recordings from 49 patients, totaling 5303 h of 16-channel recording. They showed that 24% of the 244 seizures recorded were missed by the automatic detection; in 41% of the seizures, the patient alarm was not pressed but the computer made detections. The false detection rate was of the order of 1 false detection per hour of recording. Conclusions are: (1) automatic seizure detection must be used in conjunction with a patient alarm button since some seizures, having poorly defined EEG activity, are not detected; (2) the automatic detection allowed capture of many seizures, clinical and subclinical, for which the alarm was not pressed; (3) the low false detection rate indicates that lower detection threshold could be used, yielding better seizure detection.     

The prognostic significance of interictal epileptiform activity in postoperative EEGs of patients with mesial temporal lobe epilepsy.

It has not been established whether electroencephalography (EEG) is a contributing factor in predicting the outcome of surgery for epilepsy. We conducted a prospective study on 26 patients (M/F 14/12, age: 33 +/- 7.5 years, range 19-48) with mesial temporal lobe epilepsy (MTLE) who were followed for 2 years after surgery and who underwent routine EEG recordings 5.6 +/- 3 months (range 3-12) postoperatively. Interictal epileptiform activity (IEA) on the EEG was compared in 17 seizure-free patients to 9 patients with recurrent seizures. The two groups were similar in gender, age, febrile convulsions, trauma, family history, seizure frequency prior to surgery, epilepsy duration and number of antiepileptic drugs. Following surgery, 17 study patients (65%) became seizure free; 9 (35%) had seizure recurrence. Post-operative EEG recordings showed IEA in 8/26 study patients (31%), 3 of whom were from the seizure-free group (3/17, 18%); 5 had seizure recurrence (5/9, 56%) (p=0.078). IEAs in postoperative EEGs were less frequently demonstrated in patients who were seizure free, but the presence of postoperative IEAs does not preclude successful surgical outcome.     

Auditory event-related potentials (P300) in the identification of psychogenic nonepileptic seizures

The feasibility and conceivable value of postictal event-related potential (ERP) recordings were studied in patients with nonepileptic seizures (NES) admitted for long-term video/EEG monitoring. Ten patients with NES underwent preictal (on hospital admission) and postictal (< or =6 hours after seizure) ERP recordings of an auditory oddball paradigm. Additionally, 10 temporal lobe epilepsy (TLE) patients with partial seizures and secondary generalization underwent preictal, postictal (< 6 hours after seizures), and interictal (7-48 hours after seizure) ERP recordings. We recently reported that ERPs recorded in TLE patients with partial epilepsy undergo a temporary change postictally, while returning to their preictal state during interictal recordings. In the current study intraclass correlations, transformed into z scores, are used to determine test-retest validity of repeated ERP recordings. An independent sample t test with z scores for the comparison of preictal and postictal recordings showed that ERP activation differed between NES and TLE patients (P=0.009). More specifically, ERP recordings in the preictal and postictal states were similar in NES patients, but dissimilar in TLE patients. On the other hand, this dissimilarity in ERPs disappeared when comparing z scores for the preictal and postictal recordings in NES patients with z scores for the preictal and interictal recordings in TLE patients. This further supports the notion that identical waveforms during preictal and postictal recordings in NES patients reflect nonepileptic seizure activity. The current findings suggest that postictal ERP recordings are useful in the diagnosis of NES and differentiate TLE from NES.     

Characteristic phasic evolution of convulsive seizure in PCDH19‐related epilepsy

PCDH19‐related epilepsy is a genetic disorder that was first described in 1971, then referred to as “epilepsy and mental retardation limited to females”. PCDH19 has recently been identified as the responsible gene, but a detailed characterization of the seizure manifestation based on video‐EEG recording is still limited. The purpose of this study was to elucidate features of the seizure semiology in children with PCDH19‐related epilepsy. To do this, ictal video‐EEG recordings of 26 convulsive seizures in three girls with PCDH19‐related epilepsy were analysed. All seizures occurred in clusters, mainly during sleep accompanied by fever. The motor manifestations consisted of six sequential phases: “jerk”, “reactive”, “mild tonic”, “fluttering”, “mild clonic”, and “postictal”. Some phases were brief or lacking in some seizures, whereas others were long or pronounced. In the reactive phase, the patients looked fearful or startled with sudden jerks and turned over reactively. The tonic and clonic components were less intense compared with those of typical tonic‐clonic seizures in other types of epilepsy. The fluttering phase was characterised initially by asymmetric, less rhythmic, and less synchronous tremulous movement and was then followed by the subtle clonic phase. Subtle oral automatism was observed in the postictal phase. The reactive, mild tonic, fluttering and mild clonic phases were most characteristic of seizures of PCDH19‐related epilepsy. Ictal EEG started bilaterally and was symmetric in some patients but asymmetric in others. It showed asymmetric rhythmic discharges in some seizures at later phases. The electroclinical pattern of the phasic evolution of convulsive seizure suggests a focal onset seizure with secondary generalisation. Based on our findings, we propose that the six unique sequential phases in convulsive seizures suggest the diagnosis of PCDH19‐related epilepsy when occurring in clusters with or without high fever in girls. [Published with video sequences online]     

Association of seizures with cortical spreading depression and peri-infarct depolarisations in the acutely injured human brain

OBJECTIVE: To test the co-occurrence and interrelation of ictal activity and cortical spreading depressions (CSDs) - including the related periinfarct depolarisations in acute brain injury caused by trauma, and spontaneous subarachnoid and/or intracerebral haemorrhage. METHODS: 63 patients underwent craniotomy and electrocorticographic (ECoG) recordings were taken near foci of damaged cortical tissue for up to 10 days. RESULTS: 32 of 63 patients exhibited CSDs (5-75 episodes) and 11 had ECoGraphic seizure activity (1-81 episodes). Occurrence of seizures was significantly associated with CSD, as 10 of 11 patients with seizures also had CSD (p=0.007, 2-tailed Fishers exact test). Clinically overt seizures were only observed in one patient. Each patient with CSD and seizures displayed one of four different patterns of interaction between CSD and seizures. In four patients CSD was immediately preceded by prolonged seizure activity. In three patients the two phenomena were separated in time: multiple CSDs were replaced by ictal activity. In one patient seizures appeared to trigger repeated CSDs at the adjacent electrode. In 2 patients ongoing repeated seizures were interrupted each time CSD occurred. CONCLUSIONS: Seizure activity occurs in association with CSD in the injured human brain. SIGNIFICANCE: ECoG recordings in brain injury patients provide insight into pathophysiological mechanisms, which are not accessible by scalp EEG recordings.     

Changes in blood-brain barrier permeability during hot water-induced seizures in rats

Abstract. Hot water epilepsy (HWE) was induced in freely moving Wistar rats by applying hot water jets over the head region. The status of the blood-brain barrier (BBB) during the seizures and during hot water-induced hyperthermia without seizures was examined using Evans blue dye. In order to investigate the contribution of concomitant factors to this process, synchronized body temperature and blood pressure recordings were also made. Tonic-clonic seizure activity was observed within an average of 3.9 min (SE=0.6 min) in the rats exposed to the hot water jets; this treatment induced BBB opening in the cortical and deep brain areas. Body temperature and blood pressure increased from 36.5°±0.3°C to 40.0°±0.2°C, and from 91±3 mmHg to 153±4 mmHg, respectively. In the group of animals exposed to hot water application without inducing seizures, there were significant increases both in blood pressure and body temperature; however, the extravasation of Evans blue was not pronounced in the brains. Hot water-induced seizures, increased cerebrovascular permeability. Although high blood pressure and hyperthermia contribute to this permeability, the seizure activity is the major factor in this change.     

Clinical and electroencephalographic features of simple partial seizures

The clinical and electroencephalographic features of 87 simple partial seizures in 14 patients were studied with video-EEG telemetry. The patients were able to respond to verbal stimuli during all seizures and, later, could clearly recall ictal events. To determine whether the EEG changes in simple partial seizures could be reliably observed, a reader blindly reviewed four EEGs of equal duration for each seizure. These EEGs consisted of one ictal and three nonictal recordings obtained at predetermined times before the seizure. There were 27 motor seizures (mean duration, 86 seconds; range, 2 to 250 seconds), all involving clonic movements of the head and/or upper extremities; 8 (30%) of these had a sensory component (pain in 6, paresthesia in 2). An EEG change, usually localized spikes or sharp waves over the contralateral or both rolandic regions, was identifiable in nine (33%) of the motor seizures. The 60 nonmotor seizures (mean duration, 63 seconds; range, 8 to 375 seconds) involved a variety of symptoms, including somatosensory/special sensory (3 seizures), autonomic (26 seizures), cognitive (1 seizure), affective (14 seizures), and mixed, or more than one category of nonmotor symptoms (16 seizures). In only nine (15%) of the nonmotor seizures was there an ictal EEG change, usually localized spikes or paroxysmal theta activity over the temporal region. Overall, among the 87 simple partial seizures, only 18 (21%) revealed ictal EEG changes. Thus, a normal EEG is common during simple partial seizures and does not exclude the diagnosis.     

Utility of the Scalp-Recorded Ictal EEG in Childhood Epilepsy

PURPOSE: To evaluate the usefulness of the scalp-recorded ictal EEGs in diagnosing childhood epilepsy. METHODS: We analyzed the ictal EEGs of 259 seizures in 183 patients who visited the department of child neurology, Okayama University Medical School, during the past 6 years. RESULTS: We divided all seizures into the following four categories, according to the diagnostic usefulness of ictal EEGs in determining the seizure type: 1. (a) Ictal EEGs confirmed the diagnosis of the seizure type based on seizure symptoms (101 seizures); (b) Ictal EEGs aided in the classification of the seizure type based on the seizure symptoms (101 seizures); (c) Ictal EEGs corrected errors in the classification (37 seizures); and (d) Ictal EEGs revealed previously unreported/undocumented seizure type (20 seizures). 2. Of the 37 misdiagnosed seizures (group C), 11 were nonepileptic seizures misdiagnosed as epileptic seizures, eight were complex partial seizures (CPS) misdiagnosed as the other seizure types, and 10 were other seizure types misdiagnosed as CPSs. 3. Of the 20 previously unreported/undocumented seizures (group D), nine were myoclonic seizures, five were absence seizures, five were CPS, and one was tonic spasms. 4. Seventy-two patients had CPS. Among them, 11 patients showed no epileptic spikes in their interictal EEG recordings. Therefore, ictal recordings confirmed the diagnosis of epilepsy. CONCLUSIONS: Ictal EEG recording is a very useful diagnostic tool not only for determining seizure types, but also for uncovering the existence of the unsuspected seizure types. It supplies the physician with useful information for the classification and the treatment of epilepsy. In particular, ictal EEGs are useful in diagnosing patients with CPS.     

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.