WHO Classification of Tumours of the Central Nervous System was revised in 2016 for the 4th edition. The new classification recommends that molecular genetic information should be added to histological diagnosis and malignancy grade to achieve an integrated diagnosis in certain tumors of the central nervous system. In this article, we summarize the background information and major points regarding this revision. Currently, an optimal system for molecular genetic diagnosis with standardized test methods and financial support of the National Health Insurance has yet to be established in Japan. In 2017, the Japan Society for Neuro-Oncology has conducted a survey to understand the domestic status of molecular genetic diagnosis approaches with questionnaires sent to major neurosurgical centers. Here we present the results of this survey to elucidate the current issues related to the molecular diagnosis of central nervous system tumors and discuss future perspectives for improving management in adult patients with gliomas.
Glioma management aims to prolong patient survival while maintaining quality of life (QOL). To maintain patient QOL, it is necessary to preserve not only motor, sensory, visual, and verbal functions, but also higher brain functions that governing one’s personality. Awake surgery and electrophysiological monitoring are approaches that can help preserve brain function during operation. With regard to chemotherapy, temozolomide and bevacizumab are useful for preserving brain function through their antitumor and antiedema effects, respectively. For elderly patients who are vulnerable to radiation, short-term hypofractionated radiotherapy are considered useful for preserving brain function. In addition, NovoTTF is a therapeutic device that inhibits cell growth, and it is expected to maintain brain function through its tumor suppression effect. Drug discovery and novel technologies are expected to lead to better treatment both prolonging survival and maintaining QOL in the future.
Glioma grade Ⅱ/Ⅲ consists of various diseases based on the WHO 2016 molecular classification, and a large percentage of these diseases comprise oligodendroglial tumors harboring chromosome 1p/19q codeletion, IDH-mutant astrocytic tumors, and IDH-wild type diffuse gliomas. Since the tumor characteristics of these molecular subtypes differ, there is a need to establish a standard therapy optimized for each disease. This review presents current evidence and recommended standard therapy for grade Ⅱ/Ⅲ gliomas, and discusses several issues that must be considered. For example, a randomized phase Ⅲ study of primary high-risk, low-grade gliomas recently showed that postoperative radiotherapy and adjuvant PCV chemotherapy are effective. However, careful observation might be still an option for low-risk gliomas. Therefore, it is important to identify the factors related to tumor malignancy for each molecular subtype and determine the risk of individual tumors being affected by such factors, and then establish standard treatment strategies according to the risk categories for each disease.
Aggressive resection of intracranial gliomas, which has a positive impact on prognosis, is unfortunately associated with an increased risk of neurological complications. To preserve brain function and avoid major postoperative morbidity, various intraoperative neurophysiological monitoring methods have been introduced in clinical practice. Specifically, it is critical to understand and master the utility of monitoring by somatosensory evoked potential and motor evoked potential (MEP). Functional mapping during awake craniotomy can be used to detect individual eloquent tissues of motor function and to observe patient’s voluntary movement with an aim of preventing unexpected deficits and promote extensive resection. Corticocortical evoked potential (CCEP) is a novel method useful for functional monitoring of language-related fibers such as arcuate fiber.
Finally, the future monitoring we propose will support decision making of tumor removal by integrating information from various medical devices and positional information of navigation in time synchronization.
Molecular targeted therapy dramatically had changed the treatment of cancer patients, and the significant effect of this treatment on control of brain metastases had also been reported. The emergence of such new treatment requires reconsideration of therapeutic strategies for brain metastases. Molecular targeted therapy had no limitation of size and number of the intracranial lesions, but unfortunately were probably not curative and had risks of systemic adverse events. On the other hand, stereotactic radiation therapy may be curative for smaller brain metastases, but had limitations such as the size and the number of lesions. As described, molecular targeted therapy as systemic treatment and stereotactic radiation therapy as local treatment are not competitive treatments but complementary and coordinated treatments. Although how to coordinate these treatments is the future subject, the treatment strategy for each patient should be carefully discussed and decided by neurosurgeons, medical oncologists and radiation oncologists.
Gross total resection (GTR) of vestibular schwannomas aims at preventing tumor recurrence. A high jugular bulb (HJB) can lead to serious complications because the retrosigmoid approach requires surgical exposure through the posterior wall of the internal acoustic meatus (IAM). Unfortunately, however, there are no established strategies for approaching tumors in patients with an HJB. Here we present a case where the anterior transpetrosal approach (ATP) was used with an aim of eliminating risks associated with venous complications of a HJB.
A 51-year-old male was referred to our hospital with a diagnosis of a cerebellopontine angle tumor with only left hearing impairment. The maximum tumor diameter was 24 mm (Koos grade IV). Computed tomography-angiography revealed a large HJB. The retrosigmoid approach was considered to be associated with a risk of HJB injury during the posterior wall removal of the IAM. Therefore, we utilized the ATP approach because the tumor could be approached anatomically away from the HJB. The patient recovered well without HJB injury after GTR. HJB injury is associated with significant morbidity due to sinus rupture, infarction, and air embolism. The present case illustrates that the ATP approach can be considered as a surgical approach in patients with cerebellopontine angle tumors accompanying a HJB.