Preoperative cortical mapping is increasingly recogni-zed as a fundamental procedure for better planning thesurgical treatment of brain tumors. Brain mapping hel-ps the definition of skull opening, access route, andextent of tumor resection. Brain tumors can actuallydistort the normal functional anatomy of the cortex bydisplacing functional areas or inducing its plastic chan-ge. When this occurs in the area of the motor cortex,preoperative mapping of this functional area is impera-tive to minimize the risk of damaging motor function bysurgical intervention.Different technologies are currently available to per-form a pre-operative identification of functional brainareas. Functional magnetic resonance imaging (fMRI) isprobably the most commonly used technique. It worksby indirectly measuring metabolic (brain oxygen level)changes during a specific task. Positron emission tomo-graphy (PET likewise measures cerebral blood flow,oxygen or glucose consumption of brain areas duringpatient performance of tasks. Bot PET and fMRI have agood spatial resolution, but a low temporal resolutionand brain tumors may cause metabolic changes thatmay blur the identification of functional hypermetabo-lic areas. Electroencephalography has also been usedfor preoperative mapping, with the limitation of aninsufficient spatial resolution. Magneto-encephalo-graphy (MEG) detects magnetic fields generated bycortical activity during patient movement and has goodspatial and temporal resolution, but is a costly and notvery diffuse technique. Furthermore, all these techno-logies require the voluntary performance of a task withdifferent problems of standardization.Transcranial magnetic stimulation (TMS) is anelectrophysiological technique developed for the inve-stigation of human cortical functions. A rapidly chan-ging magnetic field induces a weak electric current byelectromagnetic induction; this can stimulate specificor general parts of the brain with minimal discomfort.Single or paired pulse TMS makes neurons in the neo-cortex under the site of stimulation to depolarize anddischarge an action potential. If used in the motor cor-tex, it produces an involuntary muscle response, na-mely a motor evoked potential (MEP), which can berecorded by electromyogram (EMG) and direct obser-vation. This can be done in real time, namely with thehighest temporal resolution. Furthermore, the deve-lopment of focally stimulating coils allowed the gain ofhigh spatial resolution.Navigated brain stimulation (NBS) is a combination ofTMS with 3-D MRI and computer analysis using a neuro-navigation system, to provide feedback on the exactposition of maximal stimulation. NBS offers differentadvantages for brain mapping over conventional tech-nologies including the fact that it does not passivelyrecord brain activity during voluntary patient move-ments. Instead, NBS actively stimulates the patient’smotor cortex recording EMG changes.Few clinical studies are currently available; they haveshown that preoperative NBS mapping of the motorcortex in brain tumor patients is consistent with preo-perative fMRI mapping and intraoperative direct corti-cal stimulation (DCS). Here we reviewed our experiencein pre-operative brain mapping using NBS and NBScombined with subcortical tractography and direct cor-tical and subcortical stimulation in patients with braintumors including gliomas and metastases.Surgical planning was obtained taking into considera-tion several factors including tumor size and depth,proximity to vessels, proximity to motor and other elo-quent areas, and its presumed histology. Furthermore,to determine the extent of resection and surgical stra-tegies, clinical and demographic characteristics of pa-tients were considered, including age, comorbidities,life expectancy, and personal abilities and preferences.Our preliminary data showed that the NBS had a clearimpact on the planning and surgery by changing theapproach, the planned extent of resection, or even theindications altogether. NBS allowed a precise mapping of the motor cortex andthe visualization of its spatial relationship to the tumor.Finally, comparison with DCS confirmed the spatial reliabi-lity of the pre-surgical brain mapping using NBS

Navigated Brain Stimulation (NBS) for pre-surgicalplanning of brain tumors

TOMASELLO, Francesco;ALAFACI, Concetta;ANGILERI, Filippo;CONTI, Alfredo;LA TORRE, Domenico
2012

Abstract

Preoperative cortical mapping is increasingly recogni-zed as a fundamental procedure for better planning thesurgical treatment of brain tumors. Brain mapping hel-ps the definition of skull opening, access route, andextent of tumor resection. Brain tumors can actuallydistort the normal functional anatomy of the cortex bydisplacing functional areas or inducing its plastic chan-ge. When this occurs in the area of the motor cortex,preoperative mapping of this functional area is impera-tive to minimize the risk of damaging motor function bysurgical intervention.Different technologies are currently available to per-form a pre-operative identification of functional brainareas. Functional magnetic resonance imaging (fMRI) isprobably the most commonly used technique. It worksby indirectly measuring metabolic (brain oxygen level)changes during a specific task. Positron emission tomo-graphy (PET likewise measures cerebral blood flow,oxygen or glucose consumption of brain areas duringpatient performance of tasks. Bot PET and fMRI have agood spatial resolution, but a low temporal resolutionand brain tumors may cause metabolic changes thatmay blur the identification of functional hypermetabo-lic areas. Electroencephalography has also been usedfor preoperative mapping, with the limitation of aninsufficient spatial resolution. Magneto-encephalo-graphy (MEG) detects magnetic fields generated bycortical activity during patient movement and has goodspatial and temporal resolution, but is a costly and notvery diffuse technique. Furthermore, all these techno-logies require the voluntary performance of a task withdifferent problems of standardization.Transcranial magnetic stimulation (TMS) is anelectrophysiological technique developed for the inve-stigation of human cortical functions. A rapidly chan-ging magnetic field induces a weak electric current byelectromagnetic induction; this can stimulate specificor general parts of the brain with minimal discomfort.Single or paired pulse TMS makes neurons in the neo-cortex under the site of stimulation to depolarize anddischarge an action potential. If used in the motor cor-tex, it produces an involuntary muscle response, na-mely a motor evoked potential (MEP), which can berecorded by electromyogram (EMG) and direct obser-vation. This can be done in real time, namely with thehighest temporal resolution. Furthermore, the deve-lopment of focally stimulating coils allowed the gain ofhigh spatial resolution.Navigated brain stimulation (NBS) is a combination ofTMS with 3-D MRI and computer analysis using a neuro-navigation system, to provide feedback on the exactposition of maximal stimulation. NBS offers differentadvantages for brain mapping over conventional tech-nologies including the fact that it does not passivelyrecord brain activity during voluntary patient move-ments. Instead, NBS actively stimulates the patient’smotor cortex recording EMG changes.Few clinical studies are currently available; they haveshown that preoperative NBS mapping of the motorcortex in brain tumor patients is consistent with preo-perative fMRI mapping and intraoperative direct corti-cal stimulation (DCS). Here we reviewed our experiencein pre-operative brain mapping using NBS and NBScombined with subcortical tractography and direct cor-tical and subcortical stimulation in patients with braintumors including gliomas and metastases.Surgical planning was obtained taking into considera-tion several factors including tumor size and depth,proximity to vessels, proximity to motor and other elo-quent areas, and its presumed histology. Furthermore,to determine the extent of resection and surgical stra-tegies, clinical and demographic characteristics of pa-tients were considered, including age, comorbidities,life expectancy, and personal abilities and preferences.Our preliminary data showed that the NBS had a clearimpact on the planning and surgery by changing theapproach, the planned extent of resection, or even theindications altogether. NBS allowed a precise mapping of the motor cortex andthe visualization of its spatial relationship to the tumor.Finally, comparison with DCS confirmed the spatial reliabi-lity of the pre-surgical brain mapping using NBS
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11570/2335445
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