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Table 1.  

Table 1: Large Studies Investigating the Effect of Surgical Resection on Outcomes of Low-grade Glioma

Surgery Insight: The Role of Surgery in the Management of Low-Grade Gliomas: Epidemiology



The phrase 'low-grade gliomas' encompasses the entire spectrum of WHO grade I and II gliomas, which includes ependymomas, pilocytic astrocytomas, pleomorphic xanthoastrocytomas, diffuse astrocytomas, oligodendrogliomas, and mixed gliomas. Although arbitrarily clustered under the umbrella low-grade glioma nomenclature, this heterogeneous group of tumors is clinically, histologically and molecularly diverse, and is, therefore, not generally studied or discussed as a single entity. For example, WHO grade I lesions, which include pilocytic astrocytomas and gangliogliomas, are, unlike WHO grade II lesions, well circumscribed and noninfiltrative, and complete surgical resection is universally considered curative.[1] In this Review, we will limit our discussion to WHO grade II diffuse astrocytomas, oligodendrogliomas and oligoastrocytomas, all of which have similar invasive and malignant potential.

Although low-grade gliomas are less common than malignant gliomas (of which there are ~8,000 - 10,000 cases per year) and far less common than brain metastases (~75,000 - 150,000 cases per year), they are far from rare. Approximately 2,000 - 3,000 low-grade gliomas are diagnosed in the US every year, accounting for nearly 15% of all primary brain tumors.[2] According to the Central Brain Tumor Registry of the United States (CBTRUS), the various histological classes of low-grade glioma have incidences varying between 0.10 and 0.46 per 100,000 people, and a cumulative incidence of approximately 0.9 per 100,000 people.[2]

Despite the preponderance of astrocytomas, there has been an apparent increase in recent years in the incidence of pure oligodendrogliomas and of mixed oligoastrocytomas. This increase might be partly attributable to an increased tendency for neuropathologists to seek out such diagnoses, in view of the relatively favorable prognosis conveyed by an oligodendroglial component.[3] Low-grade gliomas are particularly prevalent among white people and among men, and the highest incidence is in people between 35 and 44 years of age. Low-grade astrocytomas in adults are most commonly located in the cerebral hemispheres, with a predilection for 'secondary' functional areas such as the supplementary motor area and the insular lobe.[4] Oligodendrogliomas are most commonly seen along the cerebral convexity in subcortical areas, particularly in the frontal lobe, but sporadic reports of posterior fossa oligodendrogliomas exist.

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