What are Brain and Spinal Cord Tumors?

Cancer is a group of many related diseases. All cancers begin in cells, the body's basic unit of life. Cells make up tissues, and tissues make up the organs of the body.

Normally, cells grow and divide to form new cells as the body needs them. When cells grow old and die, new cells take their place.

Sometimes this orderly process goes wrong. New cells form when the body does not need them, and old cells do not die when they should. These extra cells can form a mass of tissue called a growth or tumor.

Tumors can be benign or malignant.

Benign tumors are not cancer.
Usually, doctors can remove them. Cells from benign tumors do not spread to other parts of the body. In most cases, benign tumors do not come back after they are removed. Most important, benign tumors are rarely a threat to life.

Malignant tumors are cancer. They are generally more serious. Cancer cells can invade and damage nearby tissues and organs. Also, cancer cells can break away from a malignant tumor and enter the bloodstream or the lymphatic system. That is how cancer cells spread from the original (primary) tumor to form new tumors in other organs. The spread of cancer is called metastasis.

Brain and Spinal Cord (CNS) Tumors

Together, the brain and spinal cord make up the Central Nervous System (CNS). There are many types of brain and spinal cord tumors.

Benign brain tumors grow and press on nearby areas of the brain. They rarely spread to other tissues but may recur (return). Malignant brain tumors are likely to grow quickly and spread into other brain tissue. When a tumor grows into or presses on an area of the brain, it may stop that part of the brain from working the way it should. Both benign and malignant brain tumors can cause symptoms and need treatment.

Tumors that start in the brain are called primary brain tumors. Often, tumors found in the brain have started somewhere else in the body and spread to one or more parts of the brain. Metastatic brain tumors are more common than primary brain tumors.

The types of cancer that commonly spread to the brain are melanoma, and cancer of the breast, colon, lung and unknown primary site. The types of cancer that commonly spread to the spinal cord are lymphoma and cancer of the lung, breast, and prostate. About half of metastatic brain and spinal cord tumors are caused by lung cancer. Leukemia, breast cancer, lymphoma and gastrointestinal cancer may spread to the leptomeninges (the two innermost membranes covering the brain and spinal cord).

The Brain

The brain is composed of three main sections:

The cerebrum is the largest part of the brain. It is at the top of the head. The cerebrum controls thinking, learning, problem solving, emotions, speech, reading, writing, and voluntary movement.

The cerebellum is in the lower back of the brain (near the middle of the back of the head). It controls movement, balance, and posture.

The brain stem connects the brain to the spinal cord. It is in the lowest part of the brain (just above the back of the neck). The brain stem controls breathing, heart rate, and the nerves and muscles used in seeing, hearing, walking, talking, and eating.


The Spinal Cord

The spinal cord connects the brain to nerves in most parts of the body. It is a column of nerve tissue that runs from the brain stem down the center of the back and covered by three thin layers of tissue called membranes. These membranes are surrounded by the vertebrae (back bones). Spinal cord nerves carry messages between the brain and the rest of the body, such as a signal from the brain to cause muscles to move or from the skin to the brain about the sense of touch.

Tissues and Cells

The brain and spinal cord have many kinds of tissues and cells, which can result in the development of different types of tumors. Following are their functions:

Neurons: These are the most important cells in the brain. They carry electric signals that determine thought, memory, emotion, speech, muscle movement, and control nearly everything else of the brain and spinal cord. Neurons send signals through their nerve fibers (axons). Axons in the brain tend to be short, while those in the spinal cord can be as long as several feet. Neurons do not usually form tumors, but they are often damaged by tumors that start nearby.

Glial Cells: These are the supporting cells of the brain. Most brain and spinal cord tumors develop from glial cells. There are 3 types of glial cells – astrocytes (support and nourish neurons - also help repair damage), oligodendrocytes (create myelin - the substance that insulates nerve cell axons), and ependymal cells (which line the ventricles within the central part of the brain and form part of the pathway through which CSF flows).

Neuroectodermal Cells: They are found throughout the brain.

Meninges: These are layers of tissue that line and protect the brain and spinal cord.
Choroid Plexus: The choroid plexus is the area of the brain within the ventricles that makes CSF (which nourishes and protects the brain).

Pituitary Gland and Hypothalamus: The pituitary is a small gland at the base of the brain. It is connected to a part of the brain called the hypothalamus. Both help regulate the activity of several other glands. They also make growth hormone, which stimulates body growth, and vasopressin, which regulates water balance by the kidneys.

Pineal Gland: The pineal gland is a small endocrine gland that sits between the cerebral hemispheres. It makes melatonin, a hormone that regulates sleep, in response to changes in light.

Blood-Brain Barrier: The small blood vessels (capillaries) in the brain and spinal cord create a very selective barrier between the blood and the tissues of the central nervous system. This normally helps maintain the brain's metabolic balance and keeps harmful toxins from getting into the brain.

Tumor Types

Brain and spinal cord tumors are named based on the type of cell they formed in and where the tumor first formed in the central nervous system.Primary brain tumors can start in almost any type of tissue or cell in the brain or spinal cord. Some tumors contain a mixture of cell types.

Following are the most common brain and spinal cord tumors:

Astrocytic Tumor - These tumors begin in star-shaped brain cells called astrocytes, which help keep nerve cells healthy. Astrocytic tumors include the following: Brain Stem Glioma, Pineal Astrocytic Tumor, Pilocytic Astrocytoma (grade I), Diffuse Astrocytoma (grade II), Anaplastic Astrocytoma (grade III) and Glioblastoma (grade IV).

Oligodendroglial Tumors - This tumor type begins in brain cells called oligodendrocytes, a type of glial cell. Grades of oligodendroglial tumors include Oligodendroglioma (grade II) and Anaplastic oligodendroglioma (grade III).

Mixed Gliomas - These are brain tumors that have two types of tumor cells in it — oligodendrocytes and astrocytes. This type of tumor most often forms in the cerebrum and are Oligoastrocytoma (grade II) and Anaplastic oligoastrocytoma (grade III).

Ependymal Tumors - This tumor type 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 Ependymoma (grade I or II) and Anaplastic ependymoma (grade III).

Pineal Parenchymal Tumors - This 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 Pineocytomas (grade II) and Pineoblastomas (grade IV).

Meningeal Tumors - A meningeal tumor, also called a meningioma, forms in the meninges (thin layers of tissue 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 Meningioma (grade I) and Meningioma (grade II and III). (A hemangiopericytoma is not a meningeal tumor but is treated like a grade II or III meningioma. It often recurs after treatment and usually spreads to other parts of the body.)

Germ Cell Tumors - These impact the cells that develop into sperm in men or ova (eggs) in women. Germ cell tumors usually form in the center of the brain, near the pineal gland, and can spread to other parts of the brain and spinal cord. There are different types of germ cell tumors, which include germinomas, teratomas, embryonal yolk sac carcinomas and choriocarcinomas. Germ cell tumors can be either benign or malignant.

Sellar Region Tumors - 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, including Craniopharyngioma (grade I) and Pituitary Tumors.

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