Pathologic substrates of focal epilepsy influence the generation of high-frequency oscillations.

OBJECTIVE: Although a clear correlation has been observed between high-frequency oscillations (HFOs) and the seizure-onset zone in distinct lesions, the role of the underlying pathologic substrates in the generation of HFOs is not well established. We aimed to investigate HFO correlates of different pathologic substrates in patients with drug-resistant epilepsy, and to examine the relation of HFOs with the anatomic location of the dysplastic lesion and surrounding tissue in patients with focal cortical dysplasia (FCD). METHODS: We studied consecutive patients with drug-resistant epilepsy who underwent intracranial electroencephalography (iEEG) investigations with depth electrodes at the Montreal Neurological Institute and Hospital, between November 2004 and May 2013. Inclusion criteria were the following: a focal lesion documented by magnetic resonance imaging (MRI); EEG recording at a 2,000 Hz sampling rate; and seizures starting from depth electrode contacts placed in lesion and perilesional tissue. RESULTS: Thirty-seven patients (13 FCD, 12 mesial temporal sclerosis, five cortical atrophy, three polymicrogyria, three nodular heterotopia, and one tuberous sclerosis) were included; 18 were women (median age 34). Ripples and fast ripples were found in all lesion types, except tuberous sclerosis, which showed no fast ripples. There was a significant difference in rates of ripples and fast ripples across different lesions (p < 0.001), with higher rates in FCD, mesial temporal sclerosis, and nodular heterotopia than in atrophy, polymicrogyria, and tuberous sclerosis. Regarding patients with FCD, HFOs rates differed significantly across the three types of tissue (lesional, perilesional, and nonlesional; p < 0.001), being higher within the borders of the MRI-visible dysplastic lesion, followed by the surrounding area, and rare in the remote cortex. SIGNIFICANCE: Our findings suggest that in patients who are all intractable, the HFO rates vary with different pathologies, and reflect different types of neuronal derangements. Our results also emphasize the potential usefulness of HFOs as an additional method to better define the extent of the epileptogenic dysplastic tissue in FCD.

Temporolimbic activation by intracranial electrical stimulation.

BACKGROUND: To evaluate the results of intracranial electrical stimulation (ICES) as a pre-surgical tool in order to select the side of the operation in bitemporal lobe epilepsy (BTLE) patients who underwent depth electrode (DE) implantation. METHODS: We reviewed the files of 77 medically intractable BTLE patients who underwent ICES with positive results through implanted DEs and then were under surgical treatment. One year or more after surgery, we evaluated the outcome. ICES was performed through: 1) Square-wave bipolar stimulation with symmetrical pulses of 60 Hz for 0.5 ms was delivered by a constant current Nuclear Chicago stimulator; 2) An initial intensity of 0.5 mA, and subsequently progressively stronger currents at 1-2 and occasionally 3 or 4 mA; 3) The duration of a single stimulation was usually 5 seconds; 4) The volume of tissue effectively stimulated did not exceed 5 mm. RESULTS: We obtained habitual auras or seizures (clinical responses, CRs) in 74 patients and after-discharges, ADs in 61 of them, according to Engel's classification for post surgery outcomes. If CRs or ADs were obtained by stimulation of only one temporal lobe the result of epilepsy surgery tended to be better (Engel classes I or II) when the operation was done on the same side of positive CRs (15 cases) or ADs (14 cases), and tended to be worse (Engel classes III or IV) when the ICES had provoked bilateral responses or when the side operated on was contra-lateral to positive CRs (33 cases) or ADs (28 cases). Statistical analyses were performed in order to test these results and we found better post-operative results when the resection took place in the same side of positive responses to ICES (CRs: chi2 4.74 and p=0.0295; ADs: chi2 7.57 and p=0.0059). CONCLUSION: In addition to other methods (PET, MRI and neuropsychology) presurgical ICES can provide useful data in the process of identifying the temporal lobe to be targeted for resection in BTLE patients.

Efficacy of and morbidity associated with stereoelectroencephalography using computerized tomography--or magnetic resonance imaging-guided electrode implantation.

OBJECT: The purpose of this paper was to define the general efficacy of and morbidity associated with stereoelectroencephalography using modem methods of imaging and to particularize the risks related to specific lobes of the brain. METHODS: All patients admitted to the Montreal Neurological Institute who had undergone either computerized tomography- or magnetic resonance imaging-guided electrode implantation by one surgeon (A.O.) were reviewed. The procedure was considered efficient if the obtained information was sufficient to make a decision either in support of or against surgery. Two hundred seventeen patients underwent 224 implantations with 3022 electrodes. Complications related to each lobe were as follows: temporal lobe, two abscesses (0.54%); frontal lobe, one abscess and three hematomas (1.4%); and occipital lobe, one hypointense lesion found 1 week after electrode explantation (2.6%). Significant risk factors associated with hematomas were implantation in the frontal lobe (p < 0.05) and the use of four or more implanted electrodes (p < 0.025). General complications included the following: 26 patients, psychiatric symptoms during monitoring; one patient, meningitis; four patients, scalp cellulitis; and two patients, hemiparesis during angiography in the early 1980s. One of these latter patients maintained a mild hemiparesis and represents the only case of permanent neurological sequela in the entire series. Data obtained during recordings supported an indication for surgery in 178 patients (79.5%), excluded a surgical option in 37 patients (16.5%), and were unsatisfactory in nine patients (4%). Thus, the overall efficacy as defined previously was 96%. CONCLUSIONS: Stereoelectroencephalography is an efficient procedure with low associated morbidity. Bilateral exploration of the temporal lobes has a morbidity rate of approximately 1%. A higher risk of hematomas occurs with the implantation of four or more electrodes in the frontal lobes.

Outcome of surgical treatment in familial mesial temporal lobe epilepsy.

PURPOSE: To describe postoperative outcome in patients with familial mesial temporal lobe epilepsy (FMTLE). METHODS: We studied FMTLE patients who underwent surgical treatment for refractory seizures. FMTLE was defined when at least two individuals in a family had a clinical EEG diagnosis of MTLE. Preoperative investigation included magnetic resonance imaging (MRI), interictal/ictal EEGs, and neuropsychological evaluation. We used Engel's classification for postoperative outcome. RESULTS: To date, 20 FMTLE patients have been operated on, with 1.6 to 9.8 years of follow-up (mean, 5.5 years). Hippocampal atrophy (HA) and other signs of mesial temporal sclerosis (MTS) were present in 18 patients (15 unilateral). Seizures were recorded in 19 patients. Seventeen (85%) patients are in class I. Two patients had normal hippocampal volumes (HcV): one (5%) is in class II and the other (5%) in class IV (extratemporal seizures developed after surgery). One (5%) patient had bilateral HA and is in class III. Qualitative histopathology showed MTS with different degrees of severity. CONCLUSIONS: Refractory FMTLE patients have good surgical outcome when unilateral or clearly asymmetric HA is identified. Preoperative investigation should be the same as that in patients with sporadic refractory MTLE.

Utility of multi-modality image guidance in epilepsy surgery / La utilidad de la imagen guiada multimodal en la cirugía de la epilepsia

De abril de 1994 a septiembre de 1996 se utilizó el ISG Viewing Wand, uno de los llamados sistemas de "cirugía estereotáctica sin marco", como una valiosa ayuda en el tratamiento quirúrgico de 120 casos de epilepsia. El sistema consta de una computadora procesadora de imágenes localizada en el quirófano que crea imágenes tridimensionales, triplanares y en línea basadas en imágenes de RM y TC. Incluye además un brazo mecánico de diseño ergonómico sensible a la posición y una sonda de mano. El procedimiento quirúrgico comienza una vez que se calibra el brazo, registra determinados rasgos de la cara y el cuero cabelludo del paciente. Con rapidez y precisión se relaciona un punto en el campo quirúrgico con el punto correspondiente en la pantalla de la computadora. El sistema provee una visualización de la información del paciente permitiendo la elección de la trayectoria óptima o menos invasiva. De esta manera, se puede determinar el abordaje óptimo a determinado blanco anatómico o lesión antes y durante la cirugía. Esta orientación da al cirujano mayor confianza y una mejor comprensión de la anatomía espacial y quirúrgica. Además, el sistema es un excelente instrumento didáctico. Las modalidades de imagenología que se utilizan actualmente son: angiorresonancia, angiografía por sustracción digital (DSA) y tomografía por emisión de positrones (PET), permite al cirujano seleccionar la modalidad imagenológica que proporcione la información anatómica y funcional pertinente para cada procedimiento en particular. Una limitación del sistema actual es su incapacidad para seleccionar y reproducir los cambios morfológicos ocurridos durante el procedimiento en el volumen quirúrgico

Metástase cerebral: tratamento paliativo com radiocirurgia / Brain metastasis: palliative treatment with radiosurgery

O artigo faz avaliaçäo de 52 pacientes com metástase cerebral tratados com radiocirurgia estereotática na Universidade McGill, em Montreal. A radiocirurgia foi realizada com a técnica dinâmica em que, ao mesmo tempo, giram a mesa e a cabeça do acelerador linear de 10 MV. Todos os pacientes (56 tratamentos ao todo) foram tratados com um único isocentro e uma dose única mediana de 1800cGy na periferia da metástase. Em 88 por cento dos casos a radiocirurgia foi usada após falha de tratamento radioterápico fracionado em todo cérebro. Todos os 52 casos tiveram avaliaçäo com CT pós radiocirurgia. O seguimento mediano foi de 6 meses (variou entre 1 e 37 meses e a taxa de resposta, parcial ou completa foi de 64 por cento. Apenas 4 pacientes (7 por cento) tiveram algum tipo de complicaçäo tardia relacionada ao tratamento. Estes achados väo de encontro com dados da literatura. A radiocirurgia é tratamento pouco agrassivo, bem tolerado e com alta taxa de resposta para lesöes locais e pode ser útil para pacientes selecionaods. O seu valor definitivo, como tratamento único ou combinado com radioterapia em todo cérebro, está sendo avaliado de forma prospectiva e randomizada

Radiocirurgia estereotática no tratamento paliativo das metástases cerebrais / Stereotactic radiosurgery in the paliative treatment of brain metastases

Entre outubro de 1988 e novembro de 1993, 57 pacientes com metástase cerebral foram tratados com radiocirurgia estereotática na Universidade McGill, Canadá. Quatro pacientes foram excluídos dessa análise, deixando, portanto, um total de 53 pacientes (com 57 lesões) avaliáveis. A radiocirurgia foi realizada com a técnica da rotação dinâmica, que utiliza acelerador linear isocêntrico de 10 MV. Dose mediana de 1.800 cGy foi dada numa única fração. Em 89 por cento dos casos a radiocirurgia foi utilizada após falha do tratamento radioterápico convencional. Com seguimento mediano de seis meses, a taxa de resposta foi de 65 por cento. O tratamento foi bem tolerado e apenas quatro pacientes (7 por cento) desenvolveram complicações tardias relacionadas ao tratamento, sendo que uma paciente necessitou de craniotomia para remoção de uma área de radionecrose. Em geral, a radiocirurgia estereotática parece ser tratamento efetivo e seguro para selecionados pacientes com doença metastática cerebral recidivada pós-tratamento convencional. O seu valor como forma única de terapis na metástate cerebral isolada está sendo agora avaliada em estudos prospectivos.