18-07-2016, 11:03 AM
In 1993 the WHO ratified a new comprehensive classification of neoplasms affecting the central nervous system. The classification of brain tumors is based on the premise that each type of tumor results from the abnormal growth of a specific cell type. To the extent that the behavior of a tumor correlates with basic cell type, tumor classification dictates the choice of therapy and predicts prognosis. The new WHO system is particularly useful in this regard with only a few notable exceptions (for example all or almost all gemistocytic astrocytomas are actually anaplastic and hence grade III or even IV rather than grade II as designated by the WHO system). The WHO classification also provides a parallel grading system for each type of tumor. In this grading sytem most named tumors are of a single defined grade. The new WHO classification provides the standard for communication between different centers in the United States and around the world. An outline of this classification is provided below.
Neuroepithelial Tumors of the CNS
Astrocytic tumors [glial tumors--categories I-V, below--may also be subclassified as invasive or non-invasive, although this is not formally part of the WHO system, the non-invasive tumor types are indicated below. Categories in italics are also not recognized by the new WHO classification system, but are in common use.]
Astrocytoma (WHO grade II)
variants: protoplasmic, gemistocytic, fibrillary, mixed
Anaplastic (malignant) astrocytoma (WHO grade III)
hemispheric
diencephalic
optic
brain stem
cerebellar
Glioblastoma multiforme (WHO grade IV)
variants: giant cell glioblastoma, gliosarcoma
Pilocytic astrocytoma [non-invasive, WHO grade I]
hemispheric
diencephalic
optic
brain stem
cerebellar
Subependymal giant cell astrocytoma [non-invasive, WHO grade I]
Pleomorphic xanthoastrocytoma [non-invasive, WHO grade I]
Oligodendroglial tumors
Oligodendroglioma (WHO grade II)
Anaplastic (malignant) oligodendroglioma (WHO grade III)
Ependymal cell tumors
Ependymoma (WHO grade II)
variants: cellular, papillary, epithelial, clear cell, mixed
Anaplastic ependymoma (WHO grade III)
Myxopapillary ependymoma
Subependymoma (WHO grade I)
Mixed gliomas
Mixed oligoastrocytoma (WHO grade II)
Anaplastic (malignant) oligoastrocytoma (WHO grade III)
Others (e.g. ependymo-astrocytomas)
Neuroepithelial tumors of uncertain origin
Polar spongioblastoma (WHO grade IV)
Astroblastoma (WHO grade IV)
Gliomatosis cerebri (WHO grade IV)
Tumors of the choroid plexus
Choroid plexus papilloma
Choroid plexus carcinoma (anaplastic choroid plexus papilloma)
Neuronal and mixed neuronal-glial tumors
Gangliocytoma
Dysplastic gangliocytoma of cerebellum (Lhermitte-Duclos)
Ganglioglioma
Anaplastic (malignant) ganglioglioma
Desmoplastic infantile ganglioglioma
desmoplastic infantile astrocytoma
Central neurocytoma
Dysembryoplastic neuroepithelial tumor
Olfactory neuroblastoma (esthesioneuroblastoma)
variant: olfactory neuroepithelioma
Pineal Parenchyma Tumors
Pineocytoma
Pineoblastoma
Mixed pineocytoma/pineoblastoma
Tumors with neuroblastic or glioblastic elements (embryonal tumors)
Medulloepithelioma
Primitive neuroectodermal tumors with multipotent differentiation
medulloblastoma
variants: medullomyoblastoma, melanocytic medulloblastoma, desmoplastic medulloblastoma
cerebral primitive neuroectodermal tumor
Neuroblastoma
variant: ganglioneuroblastoma
Retinoblastoma
Ependymoblastoma
Other CNS Neoplasms
Tumors of the Sellar Region
Pituitary adenoma
Pituitary carcinoma
Craniopharyngioma
Hematopoietic tumors
Primary malignant lymphomas
Plasmacytoma
Granulocytic sarcoma
Others
Germ Cell Tumors
Germinoma
Embryonal carcinoma
Yolk sac tumor (endodermal sinus tumor)
Choriocarcinoma
Teratoma
Mixed germ cell tumors
Tumors of the Meninges
Meningioma
variants: meningothelial, fibrous (fibroblastic), transitional (mixed), psammomatous, angiomatous, microcystic, secretory, clear cell, chordoid, lymphoplasmacyte-rich, and metaplastic subtypes
Atypical meningioma
Anaplastic (malignant) meningioma
Non-menigothelial tumors of the meninges
Benign Mesenchymal
osteocartilaginous tumors
lipoma
fibrous histiocytoma
others
Malignant Mesenchymal
chondrosarcoma
hemangiopericytoma
rhabdomyosarcoma
meningeal sarcomatosis
others
Primary Melanocytic Lesions
diffuse melanosis
melanocytoma
maliganant melanoma
variant meningeal melanomatosis
Hemopoietic Neoplasms
malignant lymphoma
plasmactoma
granulocytic sarcoma
Tumors of Uncertain Histogenesis
hemangioblastoma (capillary hemangioblastoma)
Tumors of Cranial and Spinal Nerves
Schwannoma (neurinoma, neurilemoma)
cellular, plexiform, and melanotic subtypes
Neurofibroma
circumscribed (solitary) neurofibroma
plexiform neurofibroma
Malignant peripheral nerve sheath tumor (Malignant schwannoma)
epithelioid
divergent mesenchymal or epithelial differentiation
melanotic
Local Extensions from Regional Tumors
Paraganglioma (chemodectoma)
Chordoma
Chodroma
Chondrosarcoma
Carcinoma
Metastatic tumours
Unclassified Tumors
Cysts and Tumor-like Lesions
Rathke cleft cyst
Epidermoid
Dermoid
Colloid cyst of the third ventricle
Enterogenous cyst
Neuroglial cyst
Granular cell tumor (choristoma, pituicytoma)
hypothalamic neuronal hamartoma
nasal glial herterotopia
plasma cell granuloma
A number of grading systems are in common use for tumors of astrocytic lineage (i.e. astrocytomas, anaplastic astrocytomas and glioblastomas). Grades are assigned solely based on the microsopic appearance of the tumor. The numerical grade assigned for a given tumor, however, can vary depending on which grading system is used as illustrated by the following table. Thus, it is important to specify the grading system referred to when a grade is specified. The St. Anne/Mayo grade has proven to correlate better with survival than the previously common Kernohan grading system. It can only be applied to invasive tumors of astrocytic lineage; it is otherwise similar to the WHO grading system.
Neuroepithelial Tumors of the CNS
Astrocytic tumors [glial tumors--categories I-V, below--may also be subclassified as invasive or non-invasive, although this is not formally part of the WHO system, the non-invasive tumor types are indicated below. Categories in italics are also not recognized by the new WHO classification system, but are in common use.]
Astrocytoma (WHO grade II)
variants: protoplasmic, gemistocytic, fibrillary, mixed
Anaplastic (malignant) astrocytoma (WHO grade III)
hemispheric
diencephalic
optic
brain stem
cerebellar
Glioblastoma multiforme (WHO grade IV)
variants: giant cell glioblastoma, gliosarcoma
Pilocytic astrocytoma [non-invasive, WHO grade I]
hemispheric
diencephalic
optic
brain stem
cerebellar
Subependymal giant cell astrocytoma [non-invasive, WHO grade I]
Pleomorphic xanthoastrocytoma [non-invasive, WHO grade I]
Oligodendroglial tumors
Oligodendroglioma (WHO grade II)
Anaplastic (malignant) oligodendroglioma (WHO grade III)
Ependymal cell tumors
Ependymoma (WHO grade II)
variants: cellular, papillary, epithelial, clear cell, mixed
Anaplastic ependymoma (WHO grade III)
Myxopapillary ependymoma
Subependymoma (WHO grade I)
Mixed gliomas
Mixed oligoastrocytoma (WHO grade II)
Anaplastic (malignant) oligoastrocytoma (WHO grade III)
Others (e.g. ependymo-astrocytomas)
Neuroepithelial tumors of uncertain origin
Polar spongioblastoma (WHO grade IV)
Astroblastoma (WHO grade IV)
Gliomatosis cerebri (WHO grade IV)
Tumors of the choroid plexus
Choroid plexus papilloma
Choroid plexus carcinoma (anaplastic choroid plexus papilloma)
Neuronal and mixed neuronal-glial tumors
Gangliocytoma
Dysplastic gangliocytoma of cerebellum (Lhermitte-Duclos)
Ganglioglioma
Anaplastic (malignant) ganglioglioma
Desmoplastic infantile ganglioglioma
desmoplastic infantile astrocytoma
Central neurocytoma
Dysembryoplastic neuroepithelial tumor
Olfactory neuroblastoma (esthesioneuroblastoma)
variant: olfactory neuroepithelioma
Pineal Parenchyma Tumors
Pineocytoma
Pineoblastoma
Mixed pineocytoma/pineoblastoma
Tumors with neuroblastic or glioblastic elements (embryonal tumors)
Medulloepithelioma
Primitive neuroectodermal tumors with multipotent differentiation
medulloblastoma
variants: medullomyoblastoma, melanocytic medulloblastoma, desmoplastic medulloblastoma
cerebral primitive neuroectodermal tumor
Neuroblastoma
variant: ganglioneuroblastoma
Retinoblastoma
Ependymoblastoma
Other CNS Neoplasms
Tumors of the Sellar Region
Pituitary adenoma
Pituitary carcinoma
Craniopharyngioma
Hematopoietic tumors
Primary malignant lymphomas
Plasmacytoma
Granulocytic sarcoma
Others
Germ Cell Tumors
Germinoma
Embryonal carcinoma
Yolk sac tumor (endodermal sinus tumor)
Choriocarcinoma
Teratoma
Mixed germ cell tumors
Tumors of the Meninges
Meningioma
variants: meningothelial, fibrous (fibroblastic), transitional (mixed), psammomatous, angiomatous, microcystic, secretory, clear cell, chordoid, lymphoplasmacyte-rich, and metaplastic subtypes
Atypical meningioma
Anaplastic (malignant) meningioma
Non-menigothelial tumors of the meninges
Benign Mesenchymal
osteocartilaginous tumors
lipoma
fibrous histiocytoma
others
Malignant Mesenchymal
chondrosarcoma
hemangiopericytoma
rhabdomyosarcoma
meningeal sarcomatosis
others
Primary Melanocytic Lesions
diffuse melanosis
melanocytoma
maliganant melanoma
variant meningeal melanomatosis
Hemopoietic Neoplasms
malignant lymphoma
plasmactoma
granulocytic sarcoma
Tumors of Uncertain Histogenesis
hemangioblastoma (capillary hemangioblastoma)
Tumors of Cranial and Spinal Nerves
Schwannoma (neurinoma, neurilemoma)
cellular, plexiform, and melanotic subtypes
Neurofibroma
circumscribed (solitary) neurofibroma
plexiform neurofibroma
Malignant peripheral nerve sheath tumor (Malignant schwannoma)
epithelioid
divergent mesenchymal or epithelial differentiation
melanotic
Local Extensions from Regional Tumors
Paraganglioma (chemodectoma)
Chordoma
Chodroma
Chondrosarcoma
Carcinoma
Metastatic tumours
Unclassified Tumors
Cysts and Tumor-like Lesions
Rathke cleft cyst
Epidermoid
Dermoid
Colloid cyst of the third ventricle
Enterogenous cyst
Neuroglial cyst
Granular cell tumor (choristoma, pituicytoma)
hypothalamic neuronal hamartoma
nasal glial herterotopia
plasma cell granuloma
A number of grading systems are in common use for tumors of astrocytic lineage (i.e. astrocytomas, anaplastic astrocytomas and glioblastomas). Grades are assigned solely based on the microsopic appearance of the tumor. The numerical grade assigned for a given tumor, however, can vary depending on which grading system is used as illustrated by the following table. Thus, it is important to specify the grading system referred to when a grade is specified. The St. Anne/Mayo grade has proven to correlate better with survival than the previously common Kernohan grading system. It can only be applied to invasive tumors of astrocytic lineage; it is otherwise similar to the WHO grading system.