Non-diffuse Gliomas

Chapter 3 - Histology and Molecular Pathology of Gliomas

Non-diffuse gliomas include a wide spectrum of neoplasms with 3 larger subgroups: non-diffuse astrocytic tumours, ependymal tumours, “other gliomas”.

Apart from pilocytic astrocytomas and ependymomas, these gliomas are rare. Most of them are slow growing, but occasionally more aggressive examples occur.

In neuronal-glial tumours, the tumour cells show a mixture of neuronal and glial differentiation; discrimination from gliomas with entrapped neurones may be difficult.

Pilocytic astrocytomas, the most common gliomas in children, are preferentially located in the cerebellum, optic pathways, hypothalamic region and brain stem.

They typically show alternating compact and loosely structured areas (biphasic growth), with a subset of the cells having long, hair-like (piloid) cell processes.

Most pilocytic astrocytomas carry a molecular defect affecting the BRAF pathway (most frequently a BRAF fusion Gene, sometimes the BRAF V600E mutation).

A histological hallmark of ependymomas is pseudorosette formation (perivascular nuclear-free zones). True rosettes (without a central vessel) are generally less frequent.

Most ependymomas are “classic” ependymomas (WHO Grade 2 or 3); subependymomas and myxopapillary ependymomas (both Grade 1) are relatively rare.

Nowadays, improved ependymoma classification can be achieved by combining information on tumour location, histology and molecular features.

Revision Questions

  1. What are the two most frequent categories of “non-diffuse” glioma?
  2. Which pathway is often affected in pilocytic astrocytomas?
  3. What are the two histological features that indicate ependymal differentiation in a glioma?

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Last update: 18 September 2017