Intracranial Gliomas Part I - Surgery

M. F. Chernov, Y. Muragaki, S. Kesari, I. E. McCutcheon

• Publisher: S. Karger
• Year: 2017
• ISBN:
  9783318060577
• Topic: Medicine
• Subtopic: Oncology

Aggressive surgical removal is generally considered the main initial management option for most intracranial gliomas. It often results in resolution or alleviation of neurological symptoms and signs, normalizes intracranial pressure, facilitates characterization of the neoplasm, creates optimal conditions for adjuvant therapy and neurorehabilitation, and leads to prolongation of progression-free and overall survival of patients. Leading experts in neurosurgical oncology have contributed to this volume, highlighting modern principles of surgery for both newly-diagnosed and recurrent intracranial gliomas in adult as well as pediatric patients. The first of a three-volume set, it details epidemiological aspects, defines the importance of preoperative imaging, and describes current perioperative adjuvant needs. In addition, contemporary methods of intraoperative neurophysiological monitoring, the value of brain mapping for functional preservation, tips to prevent complications, and postoperative results are presented and discussed. This book and its accompanying volumes are mainly directed at neurosurgeons, neuro-oncologists and other clinicians treating patients with brain tumors.

Chernov MF, Muragaki Y, Kesari S, McCutcheon IE (eds): Intracranial Gliomas. Part I – Surgery.
Prog Neurol Surg. Basel, Karger, 2018, vol 30, pp 12–62 (DOI: 10.1159/000464376)

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Imaging of Intracranial Gliomas

Yuko Ono^a · Mikhail F. Chernov^{b, c} · Yoshihiro Muragaki^{b, c} · Takashi Maruyama^{b, c} · Kayoko Abe^a · Hiroshi Iseki^b

^aDepartment of Diagnostic Imaging and Nuclear Medicine, ^bFaculty of Advanced Techno-Surgery, and ^cDepartment of Neurosurgery, Tokyo Women’s Medical University, Tokyo, Japan

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Abstract

Combined use of contemporary radiological modalities, particularly integration of structural, metabolic, and functional imaging, provides optimal multifaceted information for detailed characterization of intracranial gliomas. It allows differentiation of the tumor from non-neoplastic pathology, its non-invasive histopathological typing and grading, prediction of patient prognosis and clinical course of the disease, detailed planning of surgical resection or biopsy, critical postoperative assessment of the residual lesion, effective surveillance during follow-up with evaluation of effectiveness of the adjuvant therapy and timely identification of recurrence, and even insights into molecular signatures of the neoplasms. Therefore, advanced neuroimaging is one of the most important cornerstones of the modern neuro-oncology.

© 2018 S. Karger AG, Basel

Introduction

Development of advanced radiological techniques for fully non-invasive visualization and characterization of the central nervous system (CNS) and its pathologies started with the invention of CT in 1972. Subsequent advancement and clinical adaptation of this technique followed by the introduction of MRI in the late 1980s revolutionized neurosurgery in general and management of intracranial tumors in particular. Nowadays, neuroimaging plays an indispensable role in primary diagnosis of brain lesions, planning of surgical procedures, choice of the optimal postoperative treatment strategy, and longitudinal follow-up of the patient. Contemporary radiological methods provide not only structural information about the tumor, but metabolic, functional, and neurophysiological data characterizing the lesion, as well as adjacent and distant brain structures. This chapter reviews modern imaging modalities utilized in patients with intracranial gliomas and highlights their application in various clinical settings.

Imaging Modalities for Intracranial Gliomas

The list of main imaging modalities used for evaluation of intracranial gliomas includes CT, variable techniques of MRI, cerebral angiography, single photon emission CT (SPECT), positron emission tomography (PET), magnetoencephalography (MEG) and navigated transcranial magnetic stimulation (nTMS). Their combined application, particularly integration of structural, metabolic, and functional methods, provides optimal multifaceted information allowing detailed diagnosis. In general, imaging of intracranial gliomas is limited to the brain, unless there is an evidence of leptomeningeal dissemination, which requires additional evaluation of the spinal cord.

Qualitative evaluation of various images by direct visual inspection is basically the most common method. Nevertheless, the complex features of glioma morphology and often subtle changes between examinations are frequently difficult to detect reliably by the naked eye [1]. A great variety of currently available computer workstations and software programs significantly facilitates managing of radiological data, particularly providing options for archiving, co-registration, 3-dimensional (3D) reconstruction and fusion of various images, as well as for different types of post-processing analysis. Quantitative evaluation of specific radiological data is mainly performed by selection of regions-of-interest (ROI) for detection of the maximal, minimal, and/or mean values, which are usually assessed relative to the parameters in the normal brain with positioning of similar ROI in the contralateral hemisphere (of note, use of referenced measurements in normal-appearing cortex or in white matter could bring different relative values). One of the main objectives of such relative evaluations is to diminish variations of the absolute measurements obtained with the use of different devices and scanning protocols. However, selection of ROI is a non-standardized operator-dependent method, generally based on the subjective opinion of the radiologist, affected by intra- and interobserver variability, and having limited reproducibility (which is important for serial investigations). Quantitative data can be additionally assessed by histogram analysis of all pixels within the ROI, which may encompass either the whole tumor or some part of it. It provides multiple measures, which sometimes may carry valuable diagnostic information.

Computed Tomography

CT remains the most simple and rapid modality for neurovisualization in patients with any brain pathology. Availability of multidetector scanners significantly reduces examination time, increases resolution, and simplifies coronal and sagittal reconstruction of images. In patients with brain tumors plain CT can provide important information [2]. Its main diagnostic value is mainly related to identification of mass effect, hydrocephalus, signs of increased intracranial pressure, bone deformations, fresh hemorrhages, and calcifications. Particularly the latter is one of the most common signs revealed on plain CT in intracranial gliomas, and is encountered in approximately 15% of cases with significant variability among different histological types of neoplasms. However, intratumoral calcifications must be carefully differentiated from other hyperdense lesions, for example, subarachnoid and intracerebral hemorrhage, polycythemia, dural sinus thrombosis, or calcifications of the cerebral arteries and aneurysms, choroid plexus, pineal body, etc. Contrast-enhanced CT may be somewhat helpful for differential diagnosis of gliomas, but in general it is significantly less informative than MRI. Due to beam-hardening artifacts produced by the skull base, utility of CT for evaluation of basal brain and posterior fossa is limited [3].

Magnetic Resonance Imaging

MRI is the most important diagnostic tool for multiplanar visualization of brain tumors. Multiparameter diagnostic information and excellent contrast resolution make it the method of choice for detecting of various soft tissue pathology. Moreover, modern MRI-based techniques provide not only structural, but also metabolic and functional information about the tumor, which can be attained within the same imaging session.

The parameters of the individual sequences used in various MRI investigations vary widely and heavily depend on magnetic field strength and other technical characteristics of the scanner. In recent years there has been widespread clinical introduction of high-field MR scanners (mainly of 3 Tesla). Their definite advantages include higher signal-to-noise ratio (SNR) – up to twice that of the 1.5 Tesla scanners depending on the sequence used, which results in shorter examination time, greater resolution of images, and makes it possible to perform high-quality metabolic and functional examinations. However, high-field MRI is associated with an increased risk of geometric distortions, which have limited impact on diagnostic performance, but may result in mislocalization errors if used for image-guided surgery or irradiation.

For structural assessment T1- (plain and post-contrast) and T2-weighted MRI are essential [1]. Fluid-attenuated inversion recovery (FLAIR) images are frequently obtained as well, since it better characterizes areas of T2 prolongation (hyperintensity) due to suppression of signal from the cerebrospinal fluid (CSF), particularly within the ventricles, and greater contrast at the border of the lesion with normal brain. Evidence-based clinical practice guidelines [2] give a level B recommendation that these four investigations should be included in the minimum MRI examination in adult patients with a newly diagnosed brain lesion suspected as low-grade glioma (LGG). However, MRI signal lacks biological specificity. Therefore, T2 hyperintensity may reflect brain edema, neoplastic infiltration, ischemic injury, infection, demyelination or treatment-induced changes, whereas contrast enhancement may be caused by hypervascularization of the lesion or increased permeability of the blood-brain barrier (BBB) induced by various factors. It is well-recognized that the contrast-enhancing area neither defines the borders of a glioma, nor indicate its most active part. These limitations necessitate additional use of metabolic and/or functional imaging for better characterization and delineation of the neoplasm; however such techniques should not be utilized for diagnostic purposes in isolation, that is, without standard structural images.

Diffusion-weighted imaging (DWI) is based on echo-planar imaging (EPI) with applied motion probe gradients (MPG) and directed to the detection of microscopic motions of water molecules. Limitation of water diffusion within the investigated voxel of brain tissue is associated with high signal intensity on DWI and corresponding decrease of the apparent diffusion coefficient (ADC). However, high signal intensity on DWI may result not only from restricted diffusion, but can be caused by so-called “T2 shine-through effect,” which reflects high T2 signal “shining through” to the DWI image without accompanying reduction of ADC. This phenomenon should be taken into consideration during the diagnostic process. In solid brain tumors high signal intensity on DWI and low ADC are associated with hypercellularity, and usually found in high-grade gliomas (HGG), lymphomas, and some metastases (e.g., of small cell carcinomas). DWI is very useful for detailed characterization of peritumoral edema, neoplastic infiltration of the adjacent brain, tumor-associated cysts, and necrotic areas. Assessment of the so-called ADC transition coefficient (ATC) provid...