Brain and spinal cord tumors are named based on the type of cell they formed in and where the tumor first formed in the CNS. The grade of a tumor may be used to tell the difference between slow- and fast-growing types of the tumor. The grade of a tumor is based on how abnormal the cancer cells look under a microscope and how quickly the tumor is likely to grow and spread.

Tumor Grading System:

• Grade I (low-grade) tumor grows slowly, has cells that look a lot like normal cells, and rarely spreads into nearby tissues. It may be possible to remove the entire tumor by surgery. Tumors of grade I are benign.
• Grade II tumor grows slowly, but may spread into nearby tissue and may recur (come back). Grade II tumors are benign and some may become a higher-grade tumor that is cancerous.
• Grade III tumor grows quickly, is likely to spread into nearby tissue, and the tumor cells look very different from normal cells.
• Grade IV (high-grade) tumor grows and spreads very quickly and the cells do not look like normal cells. There may be areas of dead cells in the tumor. Grade IV brain tumors are harder to cure than lower-grade tumors. 

Types of tumors

Astrocytic Tumors
An astrocytic tumor begins in star-shaped brain cells called astrocytes, which help keep nerve cells healthy. An astrocyte is a type of glial cell and is sometimes called a glioma. Astrocytic tumors include the following:

• Brain stem glioma forms in the stem which is the part of the brain connected to the spinal cord. It is often a high-grade tumor, which spreads widely through the brain stem and is hard to cure. A brain stem glioma rarely occurs in adults.
• Pineal astrocytic tumor forms in tissue around the pineal gland and may be any grade. The pineal gland is a tiny organ in the brain that makes melatonin, a hormone that helps control the sleeping and waking cycle.
• Pilocytic astrocytoma (grade I) grows slowly in the brain or spinal cord. It may be in the form of a cyst and rarely spreads into nearby tissues. This type of tumor is most common in children and young adults and in people with neurofibromatosis type 1 (NF1). A pilocytic astrocytoma rarely causes death.
• Diffuse astrocytoma (grade II) grows slowly, but often spreads into nearby tissues. Sometimes a diffuse astrocytoma progresses to a higher grade and becomes an anaplastic astrocytoma or a glioblastoma. A diffuse astrocytoma can form in any part of the brain but most often forms in the cerebrum. It is most common in young adults and in people with Li-Fraumeni syndrome. It is also called a low-grade diffuse astrocytoma.
• Anaplastic astrocytoma (grade III) grows quickly and spreads into nearby tissues. An anaplastic astrocytoma may progress to a higher grade and become a glioblastoma. An anaplastic astrocytoma forms most often in the cerebrum and is most common in adults. An anaplastic astrocytoma is also called a malignant astrocytoma or high-grade astrocytoma.
• Glioblastoma (grade IV) grows and spreads very quickly. A glioblastoma forms most often in the cerebrum. This type of tumor is most common in adults. This type of tumor has a poor prognosis. It is also called glioblastoma multiforme.

Oligodendroglial Tumors
An oligodendroglial tumor begins in brain cells called oligodendrocytes, which help keep nerve cells healthy. Oligodendrocytes are a type of glial cell and are sometimes called glioma. Grades of oligodendroglial tumors include the following:

• Oligodendroglioma (grade II) grows and spreads slowly and the tumor cells look very much like normal cells. This type of tumor most often forms in the cerebrum. An oligodendroglioma is most common in adults.
• Anaplastic oligodendroglioma (grade III) grows quickly and the tumor cells look very different from normal cells. It may grow in one place or in many places throughout the brain. This type of cancer most often forms in the cerebrum.

Mixed Gliomas
A mixed glioma is a brain tumor that has two types of tumor cells in it — oligodendrocytes and astrocytes. This type of tumor most often forms in the cerebrum.

• Oligoastrocytoma (grade II) is a slow-growing tumor and the tumor cells don't look very different from normal cells.
• Anaplastic oligoastrocytoma (grade III) tumor has cells that look very different from normal cells.

Ependymal Tumors
An ependymal tumor usually begins in cells that line the fluid-filled spaces in the brain and around the spinal cord. Ependymal cells are a type of glial cell and are sometimes called a glioma. Grades of ependymal tumors include the following:

• Ependymoma (grade I or II) grows slowly and has cells that look very much like normal cells. There are two types of grade I ependymoma — myxopapillary ependymoma and subependymoma. These tumors are most common in adults. A grade II ependymoma grows in the ventricle and its connecting paths or in the spinal cord. It is most common in children and young adults and in people with neurofibromatosis type 2 (NF2).
• Anaplastic ependymoma (grade III) grows very quickly and has a poor prognosis.

Embryonal Cell Tumors: Medulloblastoma (Grade IV)
A medulloblastoma is a type of embryonal tumor. The tumor forms in brain cells when the fetus is beginning to develop. This type of brain tumor often begins in the cerebellum. The tumor may spread from the brain to the spine through the cerebrospinal fluid (CSF). A medulloblastoma occurs most often in children or young adults and in people with Turcot syndrome type 2 or nevoid basal cell carcinoma syndrome. 

Pineal Parenchymal Tumors
A pineal parenchymal tumor forms in parenchymal cells or pineocytes, which are the cells that make up most of the pineal gland. These tumors are different from pineal astrocytic tumors. Grades of pineal parenchymal tumors include the following:

• Pineocytomas (grade II) is a slow-growing pineal tumor that occurs most often in adults.
• Pineoblastomas (grade IV) is a rare tumor that is very likely to spread. This type of tumor is most common in children.

Meningeal Tumors
A meningeal tumor, also called a meningioma, forms in the meninges (thin layers of cells that cover the brain and spinal cord). It can form from different types of brain or spinal cord cells. A meningioma is most common in adults. Types of meningeal tumors include the following:

• Meningioma (grade I) is the most common type of meningeal tumor. A grade I meningioma is a slow-growing, benign tumor that forms most often in the dura mater (the layer of tissue that covers the brain and is closest to the skull). It is most common in women.
• Meningioma (grade II and III) is a rare, malignant meningeal tumor. It grows quickly and is likely to spread within the brain and spinal cord. A grade III meningioma is most common in men.

A hemangiopericytoma is not a meningeal tumor but is treated like a grade II or III meningioma. A hemangiopericytoma usually forms in the dura mater. It often recurs (comes back) after treatment and usually spreads to other parts of the body.

Germ Cell Tumors
A germ cell tumor forms in germ cells, which are the cells that develop into sperm in men or ova (eggs) in women. Germ cell tumors are caused by problems that occur during fetal development when the germ cells don’t migrate to the correct location and multiply in locations where they shouldn’t be.  The brain germ cell tumors usually form in the center of the brain, near the pineal gland. These tumors can spread to other parts of the brain and spinal cord. There are different types of germ cell tumors including germinomas, teratomas, embryonal yolk sac carcinomas, and choriocarcinomas. Germ cell tumors can be either benign or malignant. Most germ cell tumors occur in children and in people with Klinefelter syndrome.
 

Tumors of the Sellar Region: Craniopharyngioma (Grade I) and Pituitary Tumor
A tumor of the sellar region begins in the center of the brain, just above the back of the nose. It can form from different types of brain or spinal cord cells.

• Pituitary tumor forms in the pituitary gland, a pea-sized organ at the bottom of the brain, above the back of the nose. It makes hormones that affect other glands and many body functions, especially growth. Most pituitary tumors are benign.
• Craniopharyngioma (grade I) is a rare tumor that usually forms just above the pituitary gland. The tumor may grow into nearby tissues, including the pituitary gland and optic nerves. This can affect many functions, including hormone-making and vision. These tumors occur in adults and children.

Other Adult Brain Tumors

There are many other types of adult brain tumors that are rare and are not discussed in this summary:

• Pleomorphic xanthoastrocytoma;
• Subependymal giant cell astrocytoma;
• Astroblastoma;
• Chordoid glioma of the third ventricle;
• Gliomatosis cerebri;
• Gangliocytoma or ganglioglioma;
• Desmoplastic infantile astrocytoma or ganglioglioma;
• Dysembryoplastic neuroepithelial tumor;
• Central neurocytoma;
• Cerebellar liponeurocytoma;
• Paraganglioma;
• Ependymoblastoma;
• Supratentorial primitive neuroectodermal tumor (PNET);
• Choroid plexus papilloma or carcinoma;
• Pineal parenchymal tumors of intermediate differentiation;
• Melanocytic lesions;
• Capillary hemangioblastoma;
• Schwannoma;
• Cerebral lymphomas.

Recurrent Brain Tumors

A recurrent brain tumor is a tumor that has recurred (come back) after it has been treated. Brain tumors often recur, sometimes many years after the first tumor. The tumor may recur at the same place in the brain or in other parts of the central nervous system.

References