Abstract
BackgroundElectrocorticography (ECoG) has been utilized in many epilepsy cases however, the use of this technique for evaluating electrophysiological changes within tumoral zones is spare. Nonetheless, epileptic activities seem to arise from the neocortex surrounding the gliomas suggesting a link between epileptogenesis and glioma cell infiltration in the peritumoral area. The purpose of this study was to implement novel scale-free measures to assess how cortical physiology is altered by the presence of an invasive brain tumor.MethodsTwelve patients undergoing an awake craniotomy for resection of a supratentorial glioma were included. ECoG data over the main tumor and the exposed surroundings was acquired intra-operatively just prior to tumor resection. Six of the patients presented with seizures and had data acquired both in the awake and anesthetic state. The corresponding anatomical location of each electrode in relation to the macroscopically-detectable tumor was recorded using the neuronavigation system based on structural anatomical images obtained pre-operatively. The electrodes were classified into tumoral, healthy or peritumoral based on the macroscopically detectable tumoral tissue from the pre-operative structural MRI.ResultsThe electrodes overlying the tumoral tissue revealed higher power law exponent (PLE) values across tumoral area compared to the surrounding tissues. The difference between the awake and anesthetic states was significant in the tumoral and healthy tissue (p < 0.05) but not in the peritumoral tissue. The absence of a significant PLE reduction in the peritumoral tissue from the anesthetic to the awake state could be considered as an index of the presence or absence of infiltration of tumor cells into the peritumoral tissue.ConclusionsThe current study portrays for the first time distinct power law exponent features in the tumoral tissue, which could provide a potential novel electrophysiological marker in the future. The distinct features seen in the peritumoral tissue of gliomas seem to indicate the area where both the onset of epileptiform activity and the tumor infiltration take place.
Highlights
The main presenting symptom of low-grade gliomas are seizures, the pathophysiological mechanisms and related structuralfunctional abnormalities underlying the epileptogenesis in patients with these tumors remain unclear [1,2,3].The recording of electrical changes in the brain by electrodes placed directly on the cerebral cortex, electrocorticography (ECoG), has previously been used for delineation of tumors when the noninvasive imaging techniques were not yet available
In a systematic review performed on this subject, using medical subject headings and text words related to ECoG, epilepsy and gliomas in MEDLINE (OVID interface, 1946 onward), EMBASE (OVID interface, 1947 onward), and the Cochrane Central Register of Controlled Trials, we found only nine articles using EEG or ECoG for assessment of gliomarelated electrophysiological changes (Figure 1)
Once the patient was brought into moderate sedation with boluses of intravenous propofol, the head was fixed into its fitted position using a custom-designed high-field MRI-safe head holder (DORO Radiolucent Headrest System, Pro Med Instruments GmbH, Freiburg, Germany), which was integrated with an intraoperative MR imaging system (IMRISTM)
Summary
The main presenting symptom of low-grade gliomas are seizures, the pathophysiological mechanisms and related structuralfunctional abnormalities underlying the epileptogenesis in patients with these tumors remain unclear [1,2,3].The recording of electrical changes in the brain by electrodes placed directly on the cerebral cortex, electrocorticography (ECoG), has previously been used for delineation of tumors when the noninvasive imaging techniques were not yet available. The use of ECoG for cerebral tumors revealed distinct changes in the setting of infiltrative tumors [6], for instance slow delta-waves were found in the surrounding edema [7]. The origin of these slow waves was assumed to be related to intracranial hypertension another study analyzing the morphological and pathophysiological features of the peritumoral area concluded that those changes result from direct influence of the tumor on brain parenchyma, rather than from peritumoral edema or intracranial hypertension [8]. The purpose of this study was to implement novel scale-free measures to assess how cortical physiology is altered by the presence of an invasive brain tumor
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