Oligodendrogliomas, 1p/19q Codeleted (& IDH Mutant)

Chapter 3 - Histology and Molecular Pathology of Gliomas

Oligodendrogliomas typically show round nuclei with a clear perinuclear halo, resulting in a “fried egg” appearance and a “honeycomb” aspect of tumour cell clusters.

Unequivocal recognition of oligodendrogliomas is hindered by the lack of specific immunohistochemical markers for these tumours.

Aggressive oligodendrogliomas typically show marked mitotic activity, even in the presence of necrosis and/or florid MPV. However, these tumours are still Grade 3.

Especially in the periphery of the (often highly cellular) oligodendrogliomas, the diffuse infiltrative growth in surrounding brain tissue is generally easily identified.

Virtually all oligodendrogliomas are IDH mutant. As in diffuse IDH mutant astrocytomas, IDH1 R132H is by far the most common IDH mutation in oligodendrogliomas.

Complete 1p/19q codeletion (loss of the entire chromosome arms!) is the hallmark of oligodendrogliomas and indicates a better prognosis and therapy response.

Molecular tests for detection of molecular aberrations (including 1p/19q codeletion) may differ between centres and may yield false-positive or false-negative results.

With the integration of molecular aspects in the diagnosis of diffuse gliomas, the need for a separate/mixed oligoastrocytic glioma category will largely disappear.

CIC and FUBP1 Gene Mutations (located on chromosome 19q and 1p, respectively) are found in a subset of 1p/19q codeleted tumours; their impact on outcome is presently unclear.

Revision Questions

  1. What is the WHO malignancy grade assigned to the most malignant oligodendroglioma?
  2. Why will the diagnosis of mixed glioma/oligoastrocytoma largely disappear?
  3. What is the molecular hallmark of oligodendrogliomas?

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Last update: 18 September 2017