The classification of brain tumors is based on both histopathological characteristics and location in the brain. Ependymomas are divided into the following categories:

• Subependymoma (WHO Grade I).
• Myxopapillary ependymoma (WHO Grade I).
• Ependymoma (WHO Grade II). Variants include cellular, papillary, tanycytic, clear cell, and mixed.
• Anaplastic (also known as malignant) ependymoma (WHO Grade III).

The most recent World Health Organization (WHO) classification of brain tumors maintains the term "ependymoma" for tumors that are histologically benign and malignant ependymoma for those that have malignant characteristics.[1] These categories are based on the nuclear/cytoplasmic ratio, number of nuclei and mitotic figures, and the degree of nuclear atypia. Contemporary studies have failed to show significant differences in how these tumors behave on the basis of histologic classification alone,[2,3,4,5] although a small experience from a single-institution study suggested that patients with clear cell ependymoma may be at higher risk for treatment failure,[6] confirmation is required in a larger group of unselected patients. Myxopapillary ependymomas, which are typically benign and present in the filum terminale and cauda equina, are also considered a separate entity.

There are some subtypes of tumors that have been classified with ependymomas, although they carry a different prognosis. Ependymoblastomas, which generally behave more like medulloblastomas or cortical neuroectodermal tumors, are considered separate entities from ependymomas and are now classified with the embryonal tumors.[1] The pathologic classification of pediatric brain tumors is a specialized area that is undergoing evolution; review of the diagnostic tissue by a neuropathologist who has particular expertise in this area is strongly recommended.

References:

1. Kleihues P, Burger PC, Scheithauer BW: The new WHO classification of brain tumours. Brain Pathol 3 (3): 255-68, 1993.
2. Goldwein JW, Leahy JM, Packer RJ, et al.: Intracranial ependymomas in children. Int J Radiat Oncol Biol Phys 19 (6): 1497-502, 1990.
3. Rousseau P, Habrand JL, Sarrazin D, et al.: Treatment of intracranial ependymomas of children: review of a 15-year experience. Int J Radiat Oncol Biol Phys 28 (2): 381-6, 1994.
4. Chiu JK, Woo SY, Ater J, et al.: Intracranial ependymoma in children: analysis of prognostic factors. J Neurooncol 13 (3): 283-90, 1992.
5. Pollack IF, Gerszten PC, Martinez AJ, et al.: Intracranial ependymomas of childhood: long-term outcome and prognostic factors. Neurosurgery 37 (4): 655-66; discussion 666-7, 1995.
6. Fouladi M, Helton K, Dalton J, et al.: Clear cell ependymoma: a clinicopathologic and radiographic analysis of 10 patients. Cancer 98 (10): 2232-44, 2003.