Classification; Typing and Grading

Chapter 3 - Histology and Molecular Pathology of Gliomas

Gliomas are the most frequent primary central nervous system (CNS) tumours. They originate from glial cells or progenitor cells showing glial characteristics upon neoplastic Transformation.

Gliomas form a very heterogeneous group of tumours. For over a century, histological diagnosis formed the basis for assessment of prognosis and therapy.

Testing for underlying molecular aberrations now often leads to a more robust diagnosis. The World Health Organization (WHO) 2016 classification integrates histological and molecular aspects.

Gliomas in adults are mostly diffuse gliomas, with diffuse growth in cerebral hemispheres. Histological subtypes are diffuse astrocytoma and oligodendroglioma.

Based on histology, a WHO malignancy grade is assigned to diffuse gliomas: Grade 2 = low grade, Grade 3 = anaplastic and Grade 4 = glioblastoma.

Three main molecular subgroups of diffuse gliomas are recognised: (1) IDH (isocitrate dehydrogenase) wildtype; (2) IDH mutant & 1p/19q non-codeleted; (3) IDH mutant & 1p/19q codeleted.

Non-diffuse gliomas typically show more circumscribed growth; pilocytic astrocytomas and ependymomas are the most frequent examples.

In clinical practice, achieving a histological diagnosis of gliomas can be challenging because of imprecise diagnostic criteria and inadequate tissue sampling.

Clinical and radiological findings (especially tumour location, growth pattern, presence/absence of contrast enhancement) provide clues to the right diagnosis.

Revision Questions

  1. Why are diffuse gliomas called “diffuse”?
  2. What are the two major histological subgroups of diffuse glioma?
  3. What are the three main molecular subgroups of diffuse glioma?

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Last update: 18 September 2017