[Classification and Diagnosis of Adult-Type Diffuse Gliomas]

The Central Nervous System Tumours: WHO Classification of Tumours, 5^th ed.(WHO CNS5)incorporates molecular pathogenesis with histopathology to classify brain tumors into more biologically and narrowly defined entities. According to this approach, adult-type diffuse gliomas are classified into three tumor types: astrocytoma, IDH-mutant; oligodendroglioma, IDH-mutant and 1p/19q-codeleted; and glioblastoma, IDH-wildtype. Astrocytoma and oligodendroglioma are clearly defined as IDH-mutant tumors, and glioblastoma as an IDH-wildtype tumor. WHO CNS5 provides clear diagnostic criteria framed as "essential and desirable diagnostic criteria," including histopathological and molecular features. In this article, we summarized the diagnostic and grading criteria of adult-type diffuse gliomas, which include histopathological and molecular features. Further, we presented a clinical diagnostic workflow based on the immunohistopathological studies, molecular tests and their surrogate assays, and histopathological features to establish the diagnosis of adult-type diffuse gliomas. We also discussed the limitations of the clinical diagnostic workflow; for instance, some tumors may not fit within this classification provided by this diagnostic flow. Despite these limitations, we are required to utilize the diagnostic criteria and determine optimal treatment in the clinical setting.