Primary brain tumors are a diverse group of diseases that together constitute the most common solid tumor in childhood. Between 2,500 and 3,500 children are diagnosed in the United States each year. Immunohistochemical analysis, cytogenetic and molecular genetic findings, and measures of mitotic activity are increasingly used in tumor diagnosis and classification, and will likely alter classification and nomenclature in the future.

The classification of childhood brain tumors is based on histology and location.[1] Tumors are classically categorized as infratentorial, supratentorial, sellar, or suprasellar.

Common infratentorial (posterior fossa) tumors include:

1. Cerebellar astrocytomas (usually pilocytic but also fibrillary and, less frequently, high-grade).
2. Medulloblastomas (primitive neuroectodermal tumors [PNETs]).
3. Ependymomas (cellular, papillary, clear cell, tanycytic, or anaplastic).
4. Brain stem gliomas are typically diffuse intrinsic pontine gliomas or diffuse intrinsic high-grade tumors that are diagnosed neuroradiographically without biopsy. Focal, tectal, and exophytic cervicomedullary tumors are generally low-grade tumors.
5. Atypical teratoid/rhabdoid tumors.

Supratentorial tumors include:

1. Low-grade cerebral hemispheric astrocytomas (grade 1 [pilocytic] or grade 2).
2. High-grade or malignant astrocytomas (anaplastic astrocytomas, glioblastomas multiforme [grade 3 or grade 4]).
3. Mixed gliomas (low-grade or high-grade).
4. Oligodendrogliomas (low-grade or high-grade).
5. PNETs (including cerebral neuroblastomas, pineoblastomas, and ependymoblastomas).
6. Atypical teratoid/rhabdoid tumors.
7. Ependymomas (cellular or anaplastic).
8. Meningiomas.
9. Choroid plexus tumors (papillomas and carcinomas).
10. Pineal parenchymal tumors (pineocytomas, mixed pineal parenchymal tumors, and pineal parenchymal tumors of intermediate differentiation).
11. Neuronal and mixed neuronal glial tumors (gangliogliomas, desmoplastic infantile gangliogliomas, and dysembryoplastic neuroepithelial tumors).
12. Metastasis (rare) from extraneural malignancies.

Sellar or suprasellar tumors include:

1. Craniopharyngiomas.
2. Diencephalic astrocytomas (central tumors involving the chiasm, hypothalamus, and/or thalamus) that are generally low-grade (including astrocytomas, grade 1 [pilocytic] or grade 2).
3. Germ cell tumors (germinomas or nongerminomatous).

References

1. Kleihues P, Cavenee WK, eds.: Pathology and Genetics of Tumours of the Nervous System. Lyon, France: International Agency for Research on Cancer, 2000.