Today we’ll talk about the last glioma: ependymoma.
Guess where ependymomas arise? That’s right – near the ventricular system. In younger patients (up to about age 20) they typically occur near the fourth ventricle but in adults, the spinal cord is a more common location.
When ependymomas occur in the fourth ventricle, they are generally solid or papillary masses bulging up from the floor of the ventricle. They tend to grow slowly, but the prognosis is still poor because they are often too close to the pontine and medullary nuclei to allow for safe complete excision. When ependymomas occur in the spinal cord, the prognosis tends to be a bit better because complete excision is often possible.
Microscopically, ependymomas are usually well-differentiated. The tumor cells have regular, round to oval nuclei. They usually form some sort of structures – either canals and rosettes (in which the tumor cells try to recapitulate the embryologic ependymal canal, with long processes sticking into a lumen), or pseudorosettes (in which the tumor cells gather around vessels, with their little processes sticking out towards the wall of the vessel). Check out the image above for some nice canals. The background is usually densely fibrillary, and there’s usually GFAP (glial fibrillary acidic protein) positivity.
Some ependymomas, however, are anaplastic. These ependymomas have a greater cell density, and the cells don’t resemble ependymal cells all that much. There is increased mitotic activity and necrosis too, and they behave like you’d expect: worse than well-differentiated ependymomas.
There’s also a special kind of ependymoma called a myxopapillary ependymoma. This kind of ependymoma occurs in the filum terminale of the spinal cord, and it has some ependymoma-like cells but also some papillary structures lined by cuboidal cells in a myxoid background. If you take the whole thing out surgically, prognosis is good; but if the tumor surrounds the roots of the cauda equina, it will probably recur after surgery.
In general, ependymomas that are located in supratentorial regions or in the spinal cord tend to have a better prognosis, particularly when they are completely resected. Posterior fossa ependymomas, on the other hand, may present with hydrocephalus (due to obstruction of the fourth ventricle) and are prone to CSF dissemination (because the tumor is sitting right there in the ventricle). These ependymomas have a bad prognosis, especially in younger kids, where the 5 year survival is about 50%.
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