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Anaplastic ependymoma (WHO grade III) is a malignant glioma of ependymal origin with accelerated growth and an unfavorable outcome, particularly in children.[24] Incidence data vary considerably. No specific genetic alterations for this tumor are known. Prognostic correlations between histology and clinical outcome have been inconsistent. In a large series, no correlation between survival times and classic histopathological findings of malignancy were observed.

(Refer to the Ependymal Tumors section of this summary for treatment information. Refer to the PDQ summaries on Childhood Ependymoma Treatment and Childhood Central Nervous System Embryonal Tumors Treatment for more information.)

Neuroepithelial tumors of uncertain origin

Astroblastoma (no WHO grade) is a rare glial tumor with preferential manifestation in young adults. Histologically, it is characterized by a perivascular pattern of GFAP-positive astrocytic cells with broad, nontapering processes radiating toward a central blood vessel.[25] This is a rare tumor for which no reliable epidemiological data exist. Insufficient clinical-pathologic data are available to establish a WHO grade. The cerebral hemispheres are most affected; tumors may also develop in the corpus callosum, cerebellum, optic nerves, brain stem, and cauda equine. Low-grade astroblastomas appear to have a better prognosis than those with high-grade histological features.

Chordoid glioma of the third ventricle (provisional WHO grade II) is a rare, slow-growing glial tumor located in the third ventricle of adults. It is histologically characterized by clusters and cords of epithelioid, GFAP-expressing tumor cells within a variably mucinous stroma typically containing a lymphoplasmacytic infiltrate.[26] The mean age of patients is 46 years. The location of chordoid gliomas within the third ventricle and their attachment to hypothalamic and suprasellar structures often preclude complete resection. Postoperative tumor enlargement has been observed in 50% of the patients undergoing subtotal resections.

Gliomatosis cerebri (WHO grade III) is a rare, diffuse glial tumor that infiltrates the brain extensively, involves more than two lobes, is frequently bilateral, and often extends to the infratentorial structures and spinal cord.[27] In a large retrospective series, the peak incidence occurred in patients between the ages of 40 and 50 years. This tumor contains no specific chromosomal abnormalities or genetic alterations; however, the chromosomal changes, in general, are not similar to those seen in astrocytomas, which suggests that this tumor belongs to a separate genetic category. The prognosis is typically poor. A survival analysis that involved 124 patients revealed that 53% died within 12 months after onset of symptoms, 63% by 24 months, and 73% by 36 months.

Neuronal and mixed neuronal-glial tumors

These types of tumors are relatively uncommon and generally have a favorable prognosis.[28]

Gangliocytoma (WHO grade I) and ganglioglioma (WHO grade I or II) are well-differentiated, slow-growing neuroepithelial tumors comprised of neoplastic, mature ganglion cells, either alone (gangliocytoma) or in combination with neoplastic glial cells (ganglioglioma).[28]Anaplastic gangliogliomas (WHO grade III), i.e., gangliogliomas that show anaplastic features in their glial component, are sometimes seen; rare cases exhibit WHO grade IV (glioblastoma) changes in the glial component. These types of tumors account for 0.4% of all CNS tumors and 1.3% of all brain tumors, and can occur at any age. These types of tumors may occur throughout the CNS; most are supratentorial and involve the temporal lobe. Dysplastic gangliocytoma of the cerebellum (Lhermitte-Duclos disease) occurs in the setting of Cowden disease, which is associated with a germline mutation of the gene PTEN/MMAC1 (located on 10q23). No specific chromosomal abnormalities or molecular genetics are associated with sporadic cases. The correlation of anaplasia with clinical outcome is inconsistent.