The pathologic studies of oligodendrogliomas for the improvement of diagnostic accuracy.

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Although it is a common glioma, oligodendroglioma is often confused with other types of tumors. For the selection of appropriate therapeutic modality, it is important to establish objective diagnostic criteria and to propose an effective approach for the correct diagnosis.We evaluated the frequency of 1p loss in oligodendrogliomas and other mimics using FISH. 60% of oligodendrogliomas showed the loss, but other tumors did not. This indicates that the loss of 1p is specific to oligodendrogliomas.Then, the expression of microtubule-related proteins (tubulin, MAP-2) and oligodendrocyte lineage gene (Olig2) was immunohistochemically studied in oligodendroglial and astrocytic tumors. All proteins studied were expressed in oligodendrogliomas, but they were not specific to them.Cytologic features of oligodendrogliomas were compared with those of astrocytomas using the morphometry. Nuclei of oligodendrogliomas were significantly rounder and more regular in shape than those of astrocytomas.Finally, the ultrastructural features were not different between 1p loss (+) oligodendrogliomas and 1p loss (-) ones. They were principally composed of nondescript, oligodendrocyte-like cells in addition to rare tumor cells that show astrocytic or neuronal differentiation.Following the definition criteria, oligodendrogliomas should currently be diagnosed based on the characteristic microscopic features. Comprehensive analyses including cytology, immunohistochemistry, electron microscopy and molecular cytogenetics will improve the diagnostic accuracy. Especially, the latter is important for the therapeutic decision.