Ependymal cells line the CSF spaces of the brain, including the ventricles.
Ependymomas are uncommon in adults, but make up 4% of brain tumours in all age groups. In children they are the third most common tumour. Aside from classical ependymoma, myxopapillary and subependymoma have been cataloged.
Classical ependymoma has two peaks of incidence:
- Children under 10, where tumours typically occur in the fourth ventricle
- Adults (median age 55), with tumours usually occurring in the spinal cord (most common primary spinal cord tumour of adults)
Subependymoma is a benign condition that occurs in adults, often asymptomatically and found as incidental masses on MRI/CT brain.
Myxopapillary ependymoma may occur in all ages, but peaks at 30-50 years of age. These tumours may occasionally develop outside of the CNS, in the skin overlying the sacrum.
Aetiology and Pathogenesis
No specific causes of ependymoma have been identified. There are rare familial cases.
Myxopapillary ependymoma that occurs outside of the CNS is thought to arise from vestiges of the caudal neural tube.
Classical ependymoma, untreated, will usually be fatal due to obstruction of CSF flow through the fourth ventricle. In the spinal cord, it may cause paralysis due to destruction of neural pathways.
Subependymoma is a benign condition, but may occasionally cause disruption of CSF flow and hydrocephalus. Myxopapillary ependymoma is typically cured after surgical excision.
Symptoms and Signs
Symptoms and signs are highly dependent on the site of disease:
- Classical ependymoma of the fourth ventricle in children will usually cause presentation with headaches due to hydrocephalus and raised intracranial pressure
- Ependymoma of the spinal cord will cause weakness and sensory changes at and below the level of disease
- Myxopapillary ependymoma will often cause sacral pain or neurological symptoms in the lower limbs or pelvis.
- Subependymoma is normally an incidental finding, unless CSF obstruction has occured.
Ependymomas typically enhance with contrast administration. They will normally be found adjacent or involving the ventricles. Ependymoma may show increased density on CT due to calcification.
Tumour/Normal Tissue Features
The tumours are typically well circumscribed and adjacent to the ventricles or central spinal canal. Focal calcification is common and may give a gritty texture. Some variants may have cystic spaces.
The usual ependymoma histology shows rounded or spindled cells which have little variation. The cells often cluster around blood vessels, forming 'pseudo-rosettes'. Electron microscopy can be very useful; ependymoma cells show features related to their ependymal origin, including zona adherens junctions between cells and basal bodies that assist in anchoring cells together. Cilia can be seen on electron microscopy.
Several subtypes of ependymoma exist:
- Cellular ependymoma describes a highly cellular ependymoma, which otherwise behaves as the usual type
- Tanycytic ependymoma contains small rosettes and spindle cells, it may be difficult to characterise on light microscopy
- Clear cell ependymoma has cytological features similar to oligodendroglioma on light microscopy.
- Papillary ependymoma resembles papillary carcinomas and is very rare
- Anaplastic ependymoma contains features of anaplasia, with or without microvascular proliferation and/or necrosis. This is a grade III malignancy with a poor prognosis.
This is useful to determine CNS versus other origin, but is of less help in distinguishing between different glial tumours.
There are no specific genetic alterations seen in ependymoma.
Macroscopically these tumours are gelatinous. Microscopic examination is usually diagnostic; cuboidal ependymoma cells line mucous-filled spaces.
Small tumours are typically solid; the rarer larger tumours may develop cystic components. Calcification is common. Microscopically, the malignant cells are uniform and arranged in a lobular pattern. Electron microscopy shows features of ependymal origin. Immunohistochemistry is rarely helpful except to exclude non-CNS origin; genetic characteristics are unknown.
Staging / Classification
Ependymomas are grade II, with the exception of anaplastic ependymoma which is grade III. The uncommon variants (myxopapillary and subependymoma) are relatively benign and are assigned grade I.