Brain tumors can be metastatic and spread to the brain from other parts of the body. Or they can be primary and begin in the brain itself. In addition to tumors involving the brain, some central nervous system (CNS) tumors arise from the coverings of the brain and can affect the underlying brain. Grading, along with other factors, determine how aggressive primary CNS tumors are.
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Normal Anatomy and the Development of Brain Tumors
The CNS controls how the body works. It reads information from the senses. It also controls body temperature, sleep patterns, and movement. The brain is also the center for memory, learning, and emotions.
The three main parts of the brain are:
- Cerebrum —Thought, reason, and speech are found here. It processes sensory information from the body. It prompts and coordinates movement. It is also where emotions come from. It has two large hemispheres.
- Cerebellum —Found at the back of the head near the base. It coordinates movement and balance.
- Brain stem —This is the back and bottom part of the brain that connects to the spinal cord at the base of the neck. There are three parts—the mid-brain, pons, and medulla. These structures control breathing, digestion, and heart function. They also make up the pathway which must be crossed to send signals to and from the rest of the brain.
Other nervous system structures are:
- Meninges —Three layers of tissue (dura, arachnoid, and pia mater) that surround and protect the brain and spinal cord. They lie inside the skull and spine.
- Skull —The bony shell that surrounds and protects the brain.
- Cerebrospinal fluid (CSF)—Clear fluid that surrounds, protects, and cushions the brain and spinal cord. It can be found inside the meninges.
- Blood-brain barrier (BBB)—A barrier that stops certain substances in the blood from reaching the brain. It can keep out infections or toxins. But, it can also block medicines that may help treat the brain.
Cell division and cell death are normal. This process is meant to replace old or damaged cells. Sometimes this can continue after it is supposed to stop. This extra growth can form a tumor. It is not clear exactly what causes these problems. It may be a mix of genes and the environment.
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Types of Brain Tumors
There are two main types:
- Primary brain tumors start in the brain or in the layers around it. It is the second most common type of cancer in children and young adults.
- Secondary brain tumors come from cancer in other parts of the body. Cancer cells break away from the original site. They travel to the brain in the bloodstream. They are known as metastatic tumors. Secondary tumors are always cancerous.
The problems you have and how to treat them depend partly on where the tumor is. Most are named for the place they start:
- Meningiomas —These tumors start in the layers around the brain and spinal cord.
- Gliomas —These tumors arise within the brain and spread to brain tissue.
- Pituitary adenomas —The pituitary gland releases hormones. It is found at the base of the brain. Tumors can start in the pituitary cells.
- Nerve sheath tumors —Neurons are covered in a myelin sheath. It helps speed messages back and forth to the brain. Nerve sheath tumors often start in the peripheral nervous system. There are also some that start from the cranial nerve roots or the spinal nerve roots which are covered by the meninges. One of the most common types of nerve sheath tumors involve the nerve needed for hearing (the 8th cranial nerve).
- Medulloblastomas —Tumors that start and grow in the cerebellum. This is the brain tumor most often found in children.
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Last reviewed July 2021 by EBSCO Medical Review Board Rimas Lukas, MD Last Updated: 7/15/2021