Ependymoma pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Ahmad Al Maradni, M.D. [2]

Pathology

• Ependymomas represent a relatively broad group of glial tumours which share common origin from differentiated ependymal cells lining the ventricles of the brain or the central canal of the spinal cord. They account for ~5% of all neuroepithelial neoplasms, ~10% of all paediatric brain tumours and up to 33% of brain tumours occurring in those less than 3 years of age.
• Ependymomas can occur anywhere, but certain location are typical. Common locations include:

• Floor of the fourth ventricle (common location in children)
• Spinal cord ependymoma
• Myxopapillary ependymoma (conus medullaris)
• Supratentorial ependymoma

• The subependymomas, variant of the ependymoma, arise in the fourth ventricle but may occur in the septum pellucidum and the cervical spinal cord.

Gross Pathology

• Ependymomas are well-encapsulated tumors and usually arise from the floor of the fourth ventricle, situated in the lower back portion of the brain.

• 

  Fourth ventricle ependymomas frequently extend out of the ventricle into the subarachnoid space.

Microscopic Pathology

• Ependymomas are composed of cells with regular, round to oval nuclei. There is a variably dense fibrillary background.
• Tumor cells may form gland-like round or elongated structures that resemble the embryologic ependymal canal, with long, delicate processes extending into the lumen; more frequently present are perivascular pseudorosettes in which tumor cells are arranged around vessels with an intervening zone consisting of thin ependymal processes directed toward the wall of the vessel..
• Ependymal rosettes are rare but pathognomonic feature.

• 

  Micrograph of an ependymoma. H&E stain show pseudoressettes pattern of ependymal cells.

• 

  True ependymal rosette consisting of tumor cells arranged around well-defined lumens forming gland-like structures.<ref name=radiopaedia> Image courtesy of Dr Dharam RamnaniRadiopaedia (original file

• 

  Higher magnification of one of the true ependymal rosettes showing a collar of cells around a central lumen forming a gland-like structure.

Associated Conditions

The subependymal giant-cell astrocytoma, also called giant-cell glioma, is typically associated with tuberous sclerosis but can occur independently.

Genetics

Posterior fossa ependymoma can be divided into the following two groups based on distinctive patterns of gene expression.[12,13]

One expression-defined group occurs primarily in young children and is characterized by a largely balanced genomic profile with an increased occurrence of chromosome 1q gain and expression of genes and proteins previously shown to be associated with poor prognosis, such as tenascin C and epidermal growth factor receptor.[8,14] The second expression-defined group occurs primarily in older children and adults and is characterized by a more favorable prognosis and by numerous cytogenetic abnormalities involving whole chromosomes or chromosomal arms.[12]