Classification of Brain Tumors

The World Health Organization (WHO) classification is the most commonly used method for classifying brain tumors. It is based on pathological differences and the implicit belief that these tumors arise from specific categories of normal cells (Table 1). Brain tumors in children are for the most part primary central nervous system (CNS) neoplasms, while metastatic tumors, meningiomas and pituitary adenomas are rarely encountered. Aside from these epidemiological differences, there are other features that distinguish childhood brain tumors from their counterparts in adults. One is the relative incidence by histological type. Medulloblastomas, a class of primitive neuroectodermal tumors (PNET), occur mainly in children and young adults. In addition, the incidence of teratomas, germinomas and craniopharyngiomas is also higher in children. In general, the diversity of tumors in children is greater. Fortunately, the most malignant astro-cytic tumor, glioblastoma multiforme, is less common in children. A second major distinguishing feature is their site of origin (Table 2). Approximately one half of pediatric brain tumors arise in the posterior fossa, as compared to 10% in adults. The reason for this prediliction is unknown. In addition, germ-cell tumors, cran-iopharyngiomas and optic-pathway gliomas tend to arise either in the midline or adjacent to the midline.

Pediatric Neurosurgery, edited by David Frim and Nalin Gupta. ©2006 Landes Bioscience.

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