Types of Brain Tumors

Classifying Brain Tumors

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Tumors that develop initially in the brain are called primary brain tumors, while those that originate elsewhere in the body and spread to the brain as secondary brain tumors are called metastatic brain tumors. Unlike other cancers, primary brain tumors are not assigned a “stage.” Metastatic brain tumors are considered to be stage IV Cancer of the primary organ (i.e., breast, lung, kidney, etc.).

Primary Brain Tumors

Primary brain tumors are categorized into grades that indicate how abnormal the tumor cells appear under a microscope, the tumor’s rate of growth and the likelihood of the tumor spreading. In addition, primary brain tumors are named based on the type of cell from which they form and/or the location in the central nervous system (CNS) where the tumor first appeared.

Primary Brain Tumors by Grade

Primary brain tumor grades as established by the World Health Organization (WHO) are as follows:

Primary Brain Tumors by Cell Type/Location in the Central Nervous System

Craniopharyngioma (Grade I)

These rare tumors can form from different types of brain or spinal cord cells, but usually develop just above the pituitary gland (in the center and just above the back of the brain).

Germ Cell Tumor

This type of tumor begins in the sex cells, or germ cells, which are the cells that eventually develop into sperm in men or eggs in women. The majority of germ cell tumors appear in the ovaries or testes. However, this type of tumor can also originate in germ cell cells that become “trapped” in the brain during the fetal period. Germ cell tumors, which can be either benign or malignant, include germinomas, choriocarcinomas, embryonal yolk sac carcinomas and teratomas.

Glioma

Gliomas are brains tumors that begin in the glial cells, the supportive cells that surround, support and protect nerve cells (neurons). Also referred to as intra-axial brain tumors because they grow within the substance of the brain and often mix with normal brain tissue, gliomas are further broken down into two main types:

• Glioblastoma: Also known as glioblastoma multiforme (GBM), or grade IV astrocytoma glioblastoma is the most aggressive type of astrocytoma and the most common astrocytoma diagnosed in adults. These tumors are characterized by very abnormal-looking cells, high cell proliferation (mitoses), areas of dead tissue and the formation of new blood vessels. Glioblastomas can develop from previously existing lower grade astrocytomas (about in 10% of cases) or originate directly as grade 4 tumors (90% of cases). The former scenario occurs more often in younger individuals, while the latter is most prevalent in people age 60 and older.
• Anaplastic Gliomas: Also known as grade III astrocytomas, anaplastic gliomas are aggressive tumors characterized by irregularly shaped cells and an increased growth index compared to low-grade (grade I and II) astrocytomas. Anaplastic astrocytomas can recur and, in some cases, develop into glioblastomas.
• Low-Grade Gliomas: This category comprises certain glial cell tumors that are slower-growing, less aggressive gliomas than glioblastomas and anaplastic gliomas:
  • Astrocytomas: These gliomas develop from astrocytes, the same star-shaped supportive cells from which glioblastomas develop. Low-grade astrocytomas are slower-growing and less aggressive than glioblastoma, and as such, are easier to treat.
  • Oligodendrogliomas: Rare and slow-growing, these tumors originate in oligodendrocytes – a type of cell that produces a substance called myelin that functions as a protective, insulating sheath for axons (the very thin fibers that relay nerve impulses between neurons). Oligodendrogliomas can be either benign or malignant.
  • Mixed gliomas: Also called oligoastrocytomas, mixed gliomas have features of both astrocytomas and oligodendrogliomas.
• Medulloblastomas: Most often seen in children or young adults, medulloblastoma is a malignant brain tumor that starts in the lower back part of the brain (cerebellum). Medulloblastomas are a type of embryonal tumor, meaning they develop in the fetal (embryonic) cells of the brain.

Meningiomas

Meningiomas are tumors that form in the meninges, which is the thin layer of tissue that covers the brain and spinal cord. Also called meningeal tumors, meningiomas are most often seen in adults.

Types of meningiomas include:

• Meningioma (Grade I): A slow-growing tumor most often formed in the dura mater.
• Meningioma (Grade II and III): A rare tumor that grows more rapidly than a grade 1 meningioma and is more likely to spread to other regions of the body.

A related type of brain tumor, a hemangiopericytoma, is treated like a Grade II or III meningioma though it is not a meningeal tumor; hemangiopericytomas typically form in cells of the dura mater and can be difficult to treat with surgery.

Pineal Parenchymal Tumors

Pineal parenchymal tumors develop in pineocytes, the specialized parenchymal cells that compose the pineal gland (a small organ that secretes melatonin to regulates the sleep-wake cycle). Types of pineal parenchymal tumors include:

• Pineocytoma (Grade II): A slow-growing pineal tumor
• Pineoblastoma (Grade IV): A rare tumor that is very likely to spread

Pituitary Tumors

Pituitary tumors are abnormal growths that originate in the pituitary gland, a pea-sized organ located at the base of the brain that produces hormones that affect the way many parts of the body work. Most pituitary tumors are noncancerous. The three main types of pituitary tumors are:

• Pituitary Carcinomas: These malignant tumors spread from the pituitary gland to other areas of the brain and spinal cord or to areas of the body outside the central nervous system.
• Benign Pituitary Adenomas: These noncancerous tumors grow very slowly and do not spread from the pituitary gland to elsewhere in the body.
• Invasive Pituitary Adenomas: These noncancerous tumors can spread to the bones of the skull or below the pituitary gland to the sinus cavity.

Primary Nervous System Lymphoma

Lymphoma is a broad term for cancer that originates in cells of the lymph system. As part of the lymph system, lymphocytes (white blood cells carried in the lymph) travel in and out of the central nervous system (CNS). A primary central nervous system lymphoma (PCNSL) is a type of lymphoma that originates in lymphocytes in the brain, spinal cord, meninges (the layers that form the outer covering of the brain) or eye.

Schwannoma

Schwannomas are rare, benign tumors that begin in specialized nerve cells called Schwann cells or neurilemma cells. Schwann cells produce a myelin sheath (an insulating layer) around axons – the very thin nerve fibers that relay nerve impulses away from neurons to another neurons.

Metastatic Brain Tumors

Metastatic brain tumors begin in another part of the body and subsequently spread to the brain. In fact, metastatic brain tumors are diagnosed more frequently than primary brain tumors. Approximately 40 percent of patients with advanced-stage cancer develop some form of brain metastases. Metastatic brain tumors mostly affect middle-aged adults.

Roughly half of all metastatic brain tumors come from lung cancer. Other types of cancer that tend to spread to the brain are breast, colon, kidney, nasopharynx and melanoma cancers. In addition, leukemia, lymphoma, breast cancer and gastrointestinal cancer can sometimes spread to the leptomeninges (the two innermost membranes covering the brain and spinal cord). This type of metastatic brain cancer is called leptomeningeal carcinomatosis and sometimes occurs in brain tumor patients.