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Surgical Imaging


Intra-operative Imaging Techniques During Surgical Management of Gliomas Phiroz E Tarapore, MD,1


Edward F Chang, MD2 and Mitchel S Berger, MD, FACS, FAANS3


1. Resident; 2. Assistant Professor of Neurological Surgery and Physiology; 3. Professor and Chairman, Department of Neurological Surgery, University of California, San Francisco


Abstract


The goal of glioma surgery is to maximize tumor removal while preserving existing function. Intra-operative imaging techniques play an important part in achieving this goal. This article surveys those techniques and discusses the indications, advantages, and drawbacks of each. Structural techniques such as intra-operative magnetic resonance imaging (MRI), ultrasound, diffusion tensor imaging, and 5-aminolevulinic acid staining offer anatomic information. Functional techniques such as functional MRI, magnetoencephalography, and transcranial magnetic stimulation provide information about the functionality of brain regions. When incorporated into a frameless stereotactical neuronavigation system, these modalities increase both the efficacy and safety of glioma surgery by allowing the surgeon to achieve the most extensive and safe resection possible.


Keywords


Frameless stereotactical neuronavigation, 5-aminolevulinic acid, intra-operative ultrasound, intra-operative magnetic resonance imaging, diffusion tensor imaging, magnetoencephalography, transcranial magnetic stimulation, intra-operative imaging, functional magnetic resonance imaging


Disclosure: The authors have no conflicts of interest to declare. Received: November 1, 2011 Accepted: November 10, 2011 Citation: US Neurology, 2011;7(2):163–8 Correspondence: Phiroz E Tarapore, MD, Department of Neurological Surgery, University of California, San Francisco, 505 Parnassus Avenue, Box 0112, San Francisco, CA 94143-0112. E: taraporep@neurosurg.ucsf.edu


The goal of glioma surgery is to maximize tumor resection while preventing a new post-operative neurologic deficit. For both low- and high-grade gliomas, increased extent of resection correlates with improved progression-free survival as well as with overall survival.1–5 While some features of brain tumors can be visualized, in general, most aspects of infiltrative gliomas cannot be clearly seen by direct vision, thus making it difficult to evaluate when the resection is complete. Furthermore, identifying deeper structures in the trajectory of resection is critical to preserving subcortical white matter tracts and blood vessels. For these reasons, recent advances have made intra-operative imaging a cornerstone of modern glioma neurosurgery.


Neuroimaging techniques fall into two broad groups: structural and functional. Techniques such as frameless stereotaxy, intra-operative magnetic resonance imaging (MRI), ultrasound, diffusion tensor imaging (DTI), and 5-aminolevulinic acid (5-ALA) staining provide anatomic and structural information, helping to identify normal structures and tumoral regions. Functional techniques such as functional MRI (fMRI), magnetoencephalography (MEG), and transcranial magnetic stimulation (TMS) yield information about the functionality of given brain regions. Typically, functional imaging data are acquired pre-operatively and applied intra-operatively. Depending on the technique, navigational data are acquired either pre-operatively or intra-operatively, and applied intra-operatively. This article discusses both categories of neuroimaging, since they both have intra-operative applications and are critical to the successful management of gliomas.


© TOUCH BRIEFINGS 2011


Frameless Stereotaxy


Frameless stereotactical neuronavigation systems are the mainstay of modern image-guided neurosurgery.6


Introduced in the 1980s, frameless


stereotactical neuronavigation allows the surgeon to navigate in three dimensions within the anatomy of a specific patient in real time, making use of images that are acquired pre-operatively (see Figure 1). This technique depends on accurate co-registration between the patient and the scan. An infrared emitter and receiver system records the coordinates of each of the fiducial points on the patient’s head or the head shape in 3D space with respect to a reference arc next to the head. The software then calculates the position of the patient in space and co-registers the patient to the scan. Thereafter, touching the probe anywhere on or in the patient’s head will cause the neuronavigational system to display the relevant slices of the scan, with a crosshair indicating the position of the probe tip.


Frameless stereotactical neuronavigation has greatly improved the accuracy and safety of glioma surgery. It effectively allows a resection to be carried up to its safe margin. In so doing, this technique has been shown to improve the extent of resection and to reduce post-operative deficits.7–10


Additionally, it enables the


surgeon to tailor craniotomies with greater accuracy, allowing for smaller exposures, shorter incisions, and reduced morbidity.11


Finally,


as stated previously, frameless stereotactical neuronavigation forms the platform by which pre-operative functional imaging data may be applied intra-operatively.


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