Brain Tumors

O. Jansen and A. C. Rohr

3.1 Introduction

Various criteria can be used in the classification of intracranial tumors. It is common, for example, to classify brain tumors by their location: supratentorial tumors, infratentorial tumors, and tumors of the sellar region or skull base. Another method, relevant to surgical treatment, is to classify brain tumors as intra-axial or extra-axial, i.e., tumors that are external to the brain parenchyma or tumors that arise within the brain substance from glial and neuronal cells. Of course, some tumors undergo both intra-axial and extra-axial growth, so this classification is not always definitive. The classification of brain tumors used in this chapter is based on neuropathologic aspects. This is done to ensure complete coverage of clinically relevant tumors and also to avoid excessive duplication with tumors that may show infratentorial as well as supratentorial growth, for example. This classification and the descriptions in this chapter provide a very rigorous scheme for classifying the various brain tumors. This schematic approach is also consistent with the primary concept of this book, which will likely be used more for reference than for casual reading ( ▶ Table 3.1).

**Table 3.1** The 2007 WHO classification of brain tumors
Designation			WHO grade
Tumors of neuroepithelial tissue
Astrocytic tumors	Pilocytic astrocytoma		I
	Pilocytic astrocytoma	Pilomyxoid astrocytoma	II
	Subependymal giant cell astrocytoma		I
	Pleomorphic xanthoastrocytoma		II, III
	Diffuse astrocytoma		II
		Fibrillary astrocytoma	II
		Protoplasmic astrocytoma	II
		Gemistocytic astrocytoma	II
	Anaplastic astrocytoma		III
	Glioblastoma (multiforme)		IV
		Giant cell glioblastoma	IV
		Gliosarcoma	IV
	Gliomatosis cerebri		III, IV
Oligodendroglial tumors	Oligodendroglioma		II
Oligodendroglial tumors	Anaplastic oligodendroglioma		III
Oligoastrocytic tumors	Oligoastrocytoma		II
Oligoastrocytic tumors	Anaplastic oligoastrocytoma		III
Ependymal tumors	Subependymoma		I, II
	Myxopapillary ependymoma		I
	Ependymomas		II
		Cellular ependymoma	II
		Papillary ependymoma	II
		Clear cell ependymoma	II
		Tanycytic ependymoma	II
	Anaplastic ependymoma		III
Choroid plexus tumors	Choroid plexus papilloma		I
	Atypical choroid plexus papilloma		II
	Choroid plexus carcinoma		III
Neuroepithelial tumors of uncertain origin	Astroblastoma		II, III
	Chordoid glioma of the third ventricle		II
	Angiocentric glioma		I
Neuronal and mixed neuronal-glial tumors	Dysplastic gangliocytoma of the cerebellum		I
	Desmoplastic infantile astrocytoma/ganglioglioma		I
	Dysembryoplastic neuroepithelial tumor		I
	Gangliocytoma		I
	Ganglioglioma		I, II
	Anaplastic ganglioglioma		III
	Central neurocytoma		II
	Extraventricular neurocytoma		II
	Cerebellar liponeurocytoma		I, II
	Papillary glioneuronal tumor		I
	Rosette-forming glioneuronal tumor		I
	Paraganglioma		I
Tumors of the pineal region	Pineocytoma		I
	Pineal parenchymal tumor of intermediate differentiation		II, III
	Papillary tumor of the pineal region		II, III
	Pineoblastoma		IV
Embryonal tumors	Medulloblastoma		IV
		Desmoplastic/nodular medulloblastoma	IV
		Medulloblastoma with extensive nodularity	IV
		Anaplastic medulloblastoma	IV
		Large-cell medulloblastoma	IV
	Primitive neuroectodermal tumors		IV
		Neuroblastoma	IV
		Ganglioneuroblastoma	IV
		Ependymoblastoma	IV
		Medulloepithelioma	IV
	Atypical teratoid/rhabdoid tumor		IV
Tumors of the cranial and paraspinal nerves
Schwannoma (neurinoma)			I
		Cellular schwannoma	I
		Plexiform schwannoma	I
		Melanotic schwannoma	I
Neurofibroma			I
Neurofibroma		Plexiform neurofibroma	I
Perineurioma			I—III
		Perineurioma, not otherwise specified	I, II
		Malignant perineurioma	III
Malignant peripheral nerve sheath tumor (MPNST)			III, IV
		Epithelioid MPNST	III, IV
		MPNST with mesenchymal differentiation	III, IV
		Melanotic MPNST	III, IV
Tumors of the meninges
Tumors of meningothelial cells	Meningioma		I
		Meningothelial meningioma	I
		Fibroblastic meningioma	I
		Transitional meningioma	I
		Psammomatous meningioma	I
		Angiomatous meningioma	I
		Microcystic meningioma	I
		Secretory meningioma	I
		Lymphoplasmacyte-rich meningioma	I
		Metaplastic meningioma	I
		Choroid meningioma	II
		Clear cell meningioma	II
		Atypical meningioma	II
		Papillary meningioma	II, III
		Rhabdoid meningioma	III
		Anaplastic meningioma	III
Mesenchymal tumors	Lipoma
	Angiolipoma
	Hibermoma
	Liposarcoma
	Solitary fibrous tumor
	Fibrosarcoma
	Malignant fibrous histiocytoma
	Leiomyoma
	Leiomyosarcoma
	Rhabdomyoma
	Rhabdomyosarcoma
	Chondroma
	Chondrosarcoma
	Osteoma
	Osteosarcoma
	Osteochondroma
	Hemangioma		I
	Epithelioid hemangioendothelioma
	Hemangiopericytoma		II
	Anaplastic hemangiopericytoma		III
	Angiosarcoma
	Kaposi sarcoma
	Ewing sarcoma
Primary melanocytic lesions	Diffuse melanocytosis		I
	Melanocytoma		I
	Malignant melanoma		III, IV
	Meningeal melanomatosis		III, IV
Other neoplasms related to the meninges	Hemangioblastoma		I
Lymphomas and hematopoietic neoplasms
Malignant lymphoma
Plasmacytoma
Granulocytic sarcoma
Germ cell tumors
Germinoma			II, III
Embryonal carcinoma			IV
Yolk sac tumor			IV
Choriocarcinoma			IV
Teratoma			I—IV
		Mature teratoma
		Immature teratoma
		Teratoma with malignant transformation
Mixed germ cell tumor			II—IV
Tumors of the sellar region
Craniopharyngioma			I
		Adamantinomatous craniopharyngioma	I
		Papillary craniopharyngioma	I
Granular cell tumor			I
Pituicytoma			I
Spindle-cell oncocytoma of the adenohypophysis			I
Rhabdomyoma
Metastatic tumors			IV
Source: Louis DN, Ohgaki H, Wiestler OD et al. The 2007 WHO classification of tumours of the central nervous system. Acta Neuropathol 2007;114 (2):97–109, erratum: Acta Neuropathol 2007;114(5):547.

It is also true, however, that a range of classifications will greatly help the diagnostician in interpreting images and narrowing the differential diagnosis to one possible tumor entity. The general classification of a detected tumor as intra-axial or extra-axial will in itself greatly narrow the differential diagnosis. Further investigation of the underlying histology of a tumor will then rely on auxiliary parameters such as an infra- or supratentorial location and the age and sex of the patient. Close attention to the reaction of surrounding anatomic structures, such as the calvarium, or the reaction of the brain tissue to the tumor, will supply useful information on the growth rate and biologic behavior of a tumor and thus on whether it is benign or malignant. There is also is the principle of narrowing the diagnosis based on tumor frequency, as there is simply a greater chance of encountering a common tumor than a rare one.

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