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.

White matter functional connectivity as an additional landmark for dominant temporal lobectomy.

Dominant temporal lobectomy is classically performed based on two criteria: a perfect knowledge of the temporo-mesial microsurgical anatomy and cortical landmarks laterally. However, the functional anatomy of the subcortical white matter tracts is taken into account less, despite the risk of inducing a permanent deficit (especially aphasia) if damaged. Even if Klinger's technique allows dissection of fibres on cadaveric specimens, the exact three dimensional geometry of these fasciculi remains poorly described. Tractography, based on diffusion tensor imaging (DTI), is a powerful tool to build three dimensional images of several fasciculi, helping neurosurgeons to create a mental representation of their relationships. Moreover, intraoperative subcortical electrostimulation enables mapping of the function of these pathways. Here we review the recent findings on the white matter anatomo-functional connectivity of the dominant temporal lobe, based on combined anatomical data provided by DTI and functional information provided by intraoperative stimulation. We then discuss their implications for temporal lobectomy, by using white matter functional connectivity as an additional landmark.