Mapping and Monitoring in Glioma Surgery
Greater extent of resection (EOR) of low-grade gliomas is associated with improved survival. Proximity to eloquent cortical regions often limits resectability and elevates the risk of surgery-related deficits. Therefore, functional localization of eloquent cortex or subcortical fiber tracts can enhance the EOR and functional outcome. Imaging techniques such as functional MRI and diffusion tensor imaging fiber tracking, and neurophysiological methods like navigated transcranial magnetic stimulation and magnetoencephalography, make it possible to identify eloquent areas prior to resective surgery and to tailor indication and surgical approach but also to assess the surgical risk. Intraoperative monitoring with direct cortical stimulation and subcortical stimulation enables surgeons to preserve essential functional tissue during surgery. Through tailored pre- and intraoperative mapping and monitoring the EOR can be maximized, with reduced rates of surgery-related deficits.
Despite ongoing efforts to find effective treatments for infiltrative gliomas, progression of these tumors can only be slowed, and so far a curative treatment remains impossible. Although there haven been advancements in nonsurgical therapy and some pharmacological agents are being tested in clinical trials, early surgery and gross-total resection (GTR) play an increasingly substantiated role in prolonging overall survival in high-grade and low-grade gliomas (LGGs) and in maintaining or improving patients' quality of life.
Surgical treatment of tumors in close proximity to important functional areas or so-called eloquent areas remains a challenge, and eloquent location is a risk factor for disease progression and poor overall survival. However, the knowledge of topographical anatomy is not sufficient to determine resectability of a tumor because it does not represent functional anatomy with its interindividual variations. Therefore, to identify the relation of a tumor to an eloquent area and to define resectability, several techniques (using true electrophysiological methods or surrogate parameters of function) have evolved and have been increasingly used to guide glioma resections during recent years. Thereby, resection of tumors previously classified as unresectable became possible, with a tolerable morbidity.
In the quest to maximize the extent of resection (EOR) and to minimize morbidity, the modern neurosurgical armamentarium includes techniques to locate and identify tumor tissue by image guidance, fluorescent dyes, and intraoperative MRI, and to map and monitor critical functional areas like motor and language function, which can be achieved prior to surgery by functional MRI (fMRI), diffusion tensor imaging fiber tracking (DTI-FT), magnetoencephalography (MEG), and navigated transcranial magnetic stimulation (nTMS) and intraoperatively by direct electrical stimulation of the cortex (direct cortical stimulation [DCS]) or subcortical white matter tracts (subcortical stimulation [SCS]).
Presently, mapping and monitoring of motor and language function pre- and intraoperatively are the most established techniques, and therefore this review focuses on these two functions. We present the currently available techniques in their order of perioperative use, which can primarily be divided into preoperative mapping, intraoperative mapping, and intraoperative monitoring (Table 1). Thereby, the different techniques of preoperative mapping serve as tools to determine resectability, to estimate surgical risk and the necessity for intraoperative monitoring, and to plan the resection, including the approach. Intraoperative mapping defines resection borders and controls for preservation of neurological functions.
Abstract and Introduction
Abstract
Greater extent of resection (EOR) of low-grade gliomas is associated with improved survival. Proximity to eloquent cortical regions often limits resectability and elevates the risk of surgery-related deficits. Therefore, functional localization of eloquent cortex or subcortical fiber tracts can enhance the EOR and functional outcome. Imaging techniques such as functional MRI and diffusion tensor imaging fiber tracking, and neurophysiological methods like navigated transcranial magnetic stimulation and magnetoencephalography, make it possible to identify eloquent areas prior to resective surgery and to tailor indication and surgical approach but also to assess the surgical risk. Intraoperative monitoring with direct cortical stimulation and subcortical stimulation enables surgeons to preserve essential functional tissue during surgery. Through tailored pre- and intraoperative mapping and monitoring the EOR can be maximized, with reduced rates of surgery-related deficits.
Introduction
Despite ongoing efforts to find effective treatments for infiltrative gliomas, progression of these tumors can only be slowed, and so far a curative treatment remains impossible. Although there haven been advancements in nonsurgical therapy and some pharmacological agents are being tested in clinical trials, early surgery and gross-total resection (GTR) play an increasingly substantiated role in prolonging overall survival in high-grade and low-grade gliomas (LGGs) and in maintaining or improving patients' quality of life.
Surgical treatment of tumors in close proximity to important functional areas or so-called eloquent areas remains a challenge, and eloquent location is a risk factor for disease progression and poor overall survival. However, the knowledge of topographical anatomy is not sufficient to determine resectability of a tumor because it does not represent functional anatomy with its interindividual variations. Therefore, to identify the relation of a tumor to an eloquent area and to define resectability, several techniques (using true electrophysiological methods or surrogate parameters of function) have evolved and have been increasingly used to guide glioma resections during recent years. Thereby, resection of tumors previously classified as unresectable became possible, with a tolerable morbidity.
In the quest to maximize the extent of resection (EOR) and to minimize morbidity, the modern neurosurgical armamentarium includes techniques to locate and identify tumor tissue by image guidance, fluorescent dyes, and intraoperative MRI, and to map and monitor critical functional areas like motor and language function, which can be achieved prior to surgery by functional MRI (fMRI), diffusion tensor imaging fiber tracking (DTI-FT), magnetoencephalography (MEG), and navigated transcranial magnetic stimulation (nTMS) and intraoperatively by direct electrical stimulation of the cortex (direct cortical stimulation [DCS]) or subcortical white matter tracts (subcortical stimulation [SCS]).
Presently, mapping and monitoring of motor and language function pre- and intraoperatively are the most established techniques, and therefore this review focuses on these two functions. We present the currently available techniques in their order of perioperative use, which can primarily be divided into preoperative mapping, intraoperative mapping, and intraoperative monitoring (Table 1). Thereby, the different techniques of preoperative mapping serve as tools to determine resectability, to estimate surgical risk and the necessity for intraoperative monitoring, and to plan the resection, including the approach. Intraoperative mapping defines resection borders and controls for preservation of neurological functions.
SHARE
