Integrated Diagnostic Approach for Adult Oligodendroglioma and Oligoastrocytoma

Abstract

Diffuse gliomas with clear cell morphology are represented in the 2007 WHO classification of brain tumors as oligoastrocytomas and oligodendrogliomas of grades II and III. Although preoperative neuroimaging of these brain tumors are often successful, histopathologic evaluation of neurosurgically removed tumor specimens is still required for a definite diagnosis and subsequent molecular analysis. Such CNS tumors show an extensive variety of histological and cytological appearance making diagnosis in clear cell gliomas somewhat difficult, especially as oligoastrocytomas are often less clearly defined. There is an ongoing debate whether these tumors indeed constitute an entity or whether they represent a mixed bag containing both astrocytomas and oligodendroglioma. Recent advances with molecular data on these tumors have a major impact on neuopathological typing, prognosis and therapy of the patients. This neuro-oncologic review focuses on neuropathological and molecular features of the different types of diffusely infiltrating gliomas. Core features and distinct patterns and variants are also introduced and illustrated. Recent advances in immunohistochemistry and molecular biology have contributed to an improved classification and are discussed. Different methodologies for molecular analysis of 1p/19q codeletion, ATRX loss, MGMT promoter methylation and isocitrate dehydrogenase mutations are presented in detail and their prognostic and predictive implications for therapy are discussed.