Neuro-oncology: Brain Tumors

About a century back Harvey Cushing published the work on brain tumors. The current World Health Organization Classification of the Central Nervous System , fourth edition (WHO 2007), lists more than 120 types of brain tumors. This is broadly a histopathological classification.

How to understand about brain tumors?  We are very much familier with the nomenclature used in the older classifications . A comprehensive WHO classification of CNS tumors helps in understanding the characterstics of the brain tumors . So, while describing these tumors, for a better understading,  older terms in conjuction with newer terms should be used.

GLIOMA is the commonest primary brain tumor. Glioma arises from glial cells. Since glial cells are far more in number than neuronal cells, it will be easy to understand the fact that gliomas are more common. Glial cells comprise of astrocytes, oligodendrocytes, ependymal cells so the gliomas can further be subclassified as astrocytoma ( commonest type of glioma ), oligodendroglioma and ependymoma. According to WHO classification, these tumors can further be subclassified on the basis of features of malignancy ( microvascular proliferation, cellular atypia, mitotic activity , necrosis ) from grade I, II, III and IV.

AS neuronal cells are less in number than glial cells it is easy to remember that tumors like NEURONAL  & MIXED NEURONAL GLIAL TUMORS are less common , and relatively benign tumors . Gangliocytoma ( WHO grade I ) and ganglioglioma ( WHO grade I or III ) are well differentiated tumors composed of neoplastc mature appearing neurons alone ( gangliocytoma) or neoplastic ganglion cells combined with glioma cells ( ganglioglioma). Dysplastc gangliocytoma of the cerebellum ( Lhermitte-Duclos disease, WHO grade I ) is associated with Cowden syndrome in 50 % cases. Central Neurocytoma & extraventricular neurocytoma ( WHO grade II ) are low grade neoplasms of young adults. Paraganglioma of the filum terminale ( WHO grade I ), Papillary glioneuronal tumor ( WHO grade I ) are surgically curable tumors. Dysembryoplastic neuroepithelial tumors ( DNT; WHO grade I ) is a low grade quasihamartomatous tumor that occurs in childrenand young patients with history of long standing resistant seizures.

Astrocytomas

Can be classified as circumscribed and diffuse type.

Circumscribed Astrocytoma can further be subdivided

Pilocytic astrocytoma ( WHO Grade I ) : grow very slowly, common in children and young adults, preferentially affects the cerebellum, brainstem, optic nerves and third ventricular region.

Subependymal giant cell astrocytoma ( WHO grade I ): intraventricular , associated with tuberous sclerosis.

Desmoplastic infantile astrocytoma: rare tumor of infancy.

Pilomyxoid astrocytoma ( WHO grade II)

Pleomorphic Xanthoastrocytoma ( WHO grade II)

Diffuse astrocytoma ( WHO grade II)

Anaplastic Astrocytoma ( WHO grade III )

Glioblastoma multiforme ( GBM ) WHO grade IV , is the most common the most malignant primary brain tumor arising in adults. Microvascular proliferation, foci of necrosis are the histologic hallmarks of GBM. Pleomorphism, increased mitotic activity , positive immunostaining for GFAP ( Glial Fibrillary Acidic Protein ) are other features of GBM.

OLIGODENDRGLIOMA & OLIGOASTROCYTIC GLIAL TUMORS

Oligodendroglioma ( WHO grade II )

Anaplastic oligodendroglioma ( WHO grade III )

Mixed Diffuse gliomas with astrocytic and oligodendroglial components: Oligoastrocytoma ( WHO grade II ) and anaplastic oligoastrocytoma ( WHO grade III )

EPENDYMAL TUMORS

Myxopapillary ependymoma ( WHO grade I ): a distinct low grade variant of ependymoma that arises almost exclusively from the caudal portion of the spinal cord ( conus medullaris/ filum terminale ).

Subependymoma ( WHO grade I ) usually intraventricular

Ependymoma ( WHO grade II ) : originates from the ependymal lining of the cerebral ventricles, usually a slowly growing neoplasm of children and young adults.

Anaplastic ependymoma ( WHO grade III )