Definition
- A circumscribed glioma composed of uniform small cells with round nuclei in a fibrillary matrix and characterised by perivascular anucleate zones (pseudorosettes), ependymal rosettes in about one quarter of cases, a high nuclear-to-cytoplasmic ratio, and a high mitotic count.
Localisation
- Mainly intracranial tumours; they are rare in the spinal cord.
Grading:
- Hardly used as it does not correlate well with outcomes
Micro
- High nuclear-to-cytoplasmic ratio.
- Brisk mitotic activity, and high mitotic counts have been associated with a poor outcome in posterior fossa tumours
- Microvascular proliferation and palisading necrosis
- Pseudorosettes are a defining feature, but in some poorly differentiated supratentorial anaplastic ependymomas, they can be difficult to find.
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