Technical principles of direct bipolar electrostimulation for cortical and subcortical mapping in awake craniotomy.

INTRODUCTION: Intraoperative application of electrical current to the brain is a standard technique during brain surgery for inferring the function of the underlying brain. The purpose of intraoperative functional mapping is to reliably identify cortical areas and subcortical pathways involved in eloquent functions, especially motor, sensory, language and cognitive functions. MATERIAL AND METHODS: The aim of this article is to review the rationale and the electrophysiological principles of the use of direct bipolar electrostimulation for cortical and subcortical mapping under awake conditions. RESULTS: Direct electrical stimulation is a window into the whole functional network that sustains a particular function. It is an accurate (spatial resolution of about 5mm) and a reproducible technique particularly adapted to clinical practice for brain resection in eloquent areas. If the procedure is rigorously applied, the sensitivity of direct electrical stimulation for the detection of cortical and subcortical eloquent areas is nearly 100%. The main disadvantage of this technique is its suboptimal specificity. Another limitation is the identification of eloquent areas during surgery, which, however, could have been functionally compensated postoperatively if removed surgically. CONCLUSION: Direct electrical stimulation is an easy, accurate, reliable and safe invasive technique for the intraoperative detection of both cortical and subcortical functional brain connectivity for clinical purpose. In our opinion, it is the optimal technique for minimizing the risk of neurological sequelae when resecting in eloquent brain areas.

Resection of cavernous angioma located in eloquent areas using functional cortical and subcortical mapping under awake conditions. Outcomes in a 50-case multicentre series.

INTRODUCTION: Surgical resection of supratentorial cavernous angiomas located in eloquent areas poses a significant risk to the patient of postoperative neurological impairment and justifies intraoperative functional monitoring. METHODS: Multicentre retrospective series of adult patients with cavernous angiomas located within eloquent areas and treated with functional-based surgical resection according to functional boundaries under intraoperative functional cortico-subcortical monitoring under awake conditions. RESULTS: Fifty patients (18 males, mean 36.3±10.8 year-old) underwent surgical resection with intraoperative cortico-subcortical functional mapping using direct electrostimulation under awake conditions for a cavernous angioma located in eloquent areas with a mean postoperative follow-up of 21.0±21.2 months. At presentation, the cavernous angioma had previously resulted in severe impairment (neurological deficit in 34%, seizures in 70%, uncontrolled seizures in 34%, reduced Karnofsky Performance Status score of 70 or less in 24%, inability to work in 52%). Functional-based surgical resection allowed complete removal of the cavernous angioma in 98% and of the haemosiderin rim in 82%. Postoperative seizures and other complications were rare, and similarly so across all centres included in this series. Postoperatively, we found functional improvement in 84% of patients (reduced Karnofsky Performance Status score of 70 or less in 6%, uncontrolled seizures in 16%, and inability to work in 11%). CONCLUSION: Functional-based surgical resection aids the safe and complete resection of cavernous angiomas located in eloquent areas while minimizing the surgical risks. Functional mapping has to be considered in such challenging cases.

Direct electrical bipolar electrostimulation for functional cortical and subcortical cerebral mapping in awake craniotomy. Practical considerations.

INTRODUCTION: The aim of brain glioma surgery is to maximize the quality of resection, while minimizing the risk of sequelae. Due to the frequent location of gliomas near or within eloquent areas, owing to their infiltrative feature, and because of major interindividual variability, the anatomofunctional organization and connectivity must be studied individually. Therefore, to optimize the benefit-to-risk ratio of surgery, intraoperative functional mapping is extensively used. MATERIAL AND METHODS: This article aims at describing the rationale, indications and practical aspects of intraoperative direct electrical bipolar electrostimulation for cortical and subcortical mapping under awake conditions using the asleep-awake asleep anaesthetic protocol in the setting of cerebral gliomas. We will address the operative approach, including patient positioning, functional mapping resection strategy, anaesthetic conditions, as well as tips and pitfalls. RESULTS: The intraoperative direct electrical bipolar electrostimulation enables: (i) to study the real-time individual cortical functional organization; (ii) to study the anatomofunctional subcortical connectivity along the resection; (iii) to tailor the resection according to individual corticosubcortical functional boundaries. This is an easy, accurate, reliable, well-tolerated and safe detection technique of both cortical and subcortical functionally essential structures during resection. It should be performed in the context of a standardized protocol involving members of both anaesthesiology and neurosurgery teams at neurosurgical centers specialized in surgical neuro-oncology. CONCLUSION: Intraoperative direct electrical bipolar electrostimulation for cortical and subcortical mapping under awake conditions is currently considered the "gold standard" clinical tool for brain mapping during cerebral resection in neuro-oncology.