Benign Glioma

BenignBenign gliomaGliomas broadly refers to a heterogeneousHeterogeneous group of slow-growing glial tumors with low proliferative rates and a more indolent clinical course. These tumors may also be described as “low-grade” glioma (LGG)Low-grade glioma (LGG) and are classified as WHO gradeWHO grade I or II lesions according to the Classification of Tumors of the Central Nervous SystemCentral nervous system (CNS) (CNS) (Louis et al. in Acta Neuropathol 114:97–109, 2007). Advances in molecular geneticsGenetics have improved understanding of gliomaGliomas tumorigenesisTumorigenesis, leading to the identification of common mutationMutation profiles with significant treatment and prognostic implications. The most recent WHOWorld Health Organization (WHO) 2016 classification system has introduced several notable changes in the way that gliomasGliomas are diagnosed, with a new emphasis on molecular features as key factors in differentiationDifferentiation (Wesseling and Capper in Neuropathol Appl Neurobiol 44:139–150, 2018). BenignBenign gliomasGliomas have a predilection for younger patients and are among the most frequently diagnosed tumors in children and young adults (Ostrom et al. in Neuro Oncol 22:iv1–iv96, 2020). These tumors can be separated into two clinically distinct subgroups. The first group is of focal, well-circumscribed lesions that notably are not associated with an increased risk of malignantMalignant transformation. Primarily diagnosed in pediatric patients, these WHO gradeWHO grade I tumors may be cured with surgical resectionSurgical resection alone (Sturm et al. in J Clin Oncol 35:2370–2377, 2017). RecurrenceRecurrence rates are low, and the prognosis for these patients is excellent (Ostrom et al. in Neuro Oncol 22:iv1–iv96, 2020). Diffuse gliomasGliomas are WHO gradeWHO grade II lesions with a more infiltrativeInfiltrative pattern of growth and high propensity for recurrenceRecurrence. These tumors are primarily diagnosed in young adult patients, and classically present with seizuresSeizure (Pallud et al. Brain 137:449–462, 2014). The term “benignBenign” is a misnomer in many cases, as the natural history of these tumors is with malignantMalignant transformation and recurrenceRecurrence as grade III or grade IV tumors (Jooma et al. in J Neurosurg 14:356–363, 2019). For all LGGLow-grade glioma (LGG), surgery with maximal safe resection is the treatment of choice for both primary and recurrentRecurrent tumors. The goal of surgery should be for gross total resectionGross total resection (GTR) (GTR), as complete tumor removal is associated with higher rates of tumor control and seizureSeizure freedom. ChemotherapyChemotherapy and radiation therapyRadiation therapy (RT), while not typically a component of first-line treatment in most cases, may be employed as adjunctive therapy in high-risk or recurrentRecurrent tumors and in some select cases. The prognosisPrognosis of benignBenign gliomasGliomas varies widely; non-infiltrative tumor subtypes generally have an excellent prognosisPrognosis, while diffusely infiltrativeInfiltrative tumors, although slow-growing, are eventually fatal (Sturm et al. in J Clin Oncol 35:2370–2377, 2017). This chapter reviews the shared and unique individual features of the benignBenign gliomaGliomas including diffuse gliomaGliomas, pilocytic astrocytomaPilocytic astrocytoma and pilomyxoid astrocytomaPilomyxoid astrocytomas (PMA) (PMA), subependymal giant cell astrocytomaSubependymal giant cell astrocytomas (SEGA) (SEGA), pleomorphic xanthoastrocytomaPleomorphic xanthoastrocytoma (PXA) (PXA), subependymomaSubependymomas (SE), angiocentric gliomaAngiocentric glioma (AG), and chordoid gliomaChordoid glioma (CG). Also discussed is gangliogliomaGanglioglioma (GG), a mixed neuronal-glial tumor that represents a notable diagnosis in the differential for other LGGLow-grade glioma (LGG) (Wesseling and Capper 2018). EpendymomasEpendymomas of the brain and spinal cordSpinal cord, including major histologic subtypes, are discussed in other chapters.