There are two proposed cellular origins for ependymal tumors. These tumors may develop from:
- Ependymal central neuroepithelial cells during embryogenesis
- Malignant degeneration of mature ependymal cells in the ventricular linings of subependymal zones of cellular proliferation.
Mature ependymal cells involved. Perivascular pseudorosettes and
true ependymal rosettes are characteristic.
- Glial features lead to fibrillary appearance of the tumor.
- Glial fibrillary acidic protein (GFAP) expression is common.
- In general,
tumor cells are polygonal with large nuclei, clumped chromatin, small but distinct nucleoli
and cytoplasm which extend into processes.
Roughly one third of this tumors are high grade (anaplastic ependymoma):
- Brisk mitotic activity and vascular
- Associated with a worse prognosis
Summary of Histological Features of Ependymomas:
- Arise within or adjacent to the ependymal lining of the ventricular system
or central canal of the spinal cord.
- Infratentorial ependymomas commonest in children.
- Spinal cord ependymomas usually occur in adults.
- Supratentorial ependymomas can occur in pediatric as well as adult patients
- Soft grey-red tumors
- May be extensively cystic
- Moderately cellular tumor
- Polygonal cells
- Nuclei are generally uniform, moderately hyperchromatic and vary from round to oval
- Nucleoli are small but distinct.
- Cilia and blepharoblasts.
- Perivascular pseudorosettes.
- True ependymal rosettes
- Anaplastic features (little consensus on definition of reliable histopathological indicators of anaplasia).
- High cellularity, brisk mitotic activity, vascular proliferation and loss
of perivascular rosettes (image 1)
|Characteristic diagnostic feature
1. Anaplasia X200 - Anaplastic ependymoma with brisk mitotic activity and vascular
2. Pseudorosettes X100 - Ependymoma with typical pseudorosettes characterized
by nuclear free spaces around blood vessels.
3. Ependymal rosettes X200 - Ependymal rosettes.