Brain Tumors: Introduction

A brain tumor is an abnormal growth of tissue in the brain.

The brain is an important organ that controls thought, memory, emotion, touch, motor skills, vision, respiration, body temperature, hunger, and many other processes that regulate our body. The spinal cord is a large bundle of nerve fibers and cells that extends from the base of the brain, down the spine, to the lower back. It carries messages to and from the brain and the rest of the body.

The brain and spinal cord make up the central nervous system.

The brain has 3 main parts:

• Cerebrum. This is the upper part of the brain and the biggest part. It’s made of a right and left half (or hemisphere). Functions of the cerebrum include language (spoken and written), movement, coordination, processing of vision and hearing, judgment, reasoning, problem solving, emotions, memory, and learning.

• Cerebellum. This is the lower part of the brain. It’s located at the back of the head, just above the neck. Its function is to coordinate voluntary muscle movements and maintain posture, balance, and equilibrium.

• Brainstem. The brainstem includes the midbrain, the pons, and the medulla. It connects the spinal cord to the cerebellum. Functions of this area include movement of the eyes and mouth, sensory message relay (such as, heat or pain), hunger, breathing, consciousness, cardiac function, body temperature, involuntary muscle movements, sneezing, coughing, vomiting, and swallowing.

There are 2 main types of brain tumors:

• Primary tumors start in cells that make up the brain.

• Secondary (metastatic) tumors are made of cancer cells that started in another part of the body, then spread to the brain. In adults, secondary brain tumors are much more common than primary brain tumors.

There are 2 types of primary brain tumors:

• Benign tumor. This kind of tumor is not cancer. It tends to grow slowly. Most benign brain tumors don’t grow into nearby tissue. Once removed, they usually don’t grow back. A benign tumor can cause symptoms just like a malignant (cancer) tumor depending on how big it is and where it is in the brain.

• Malignant tumor. This kind of tumor is cancer. It usually grows fast and grows into nearby tissue. It can spread to other parts of the brain. This can make it hard to remove fully. A malignant brain tumor may grow back after treatment.

Primary brain tumors are named by the type of brain tissue they start in. The most common type of primary brain tumor is a glioma. This type starts in the supportive (glial) tissue of the brain. Some gliomas grow slowly and are called low grade. Others called high-grade gliomas grow and spread quickly. Most gliomas are malignant, but they can be benign. Some types of glioma include:

• Astrocytoma. This is the most common type of glioma. It starts in small star-shaped cells called astrocytes. In adults, an astrocytoma usually grows in the cerebrum. In children, they can grow in the cerebellum, cerebrum, or brain stem. Most astrocytomas spread into nearby normal brain tissue and are hard to cure with surgery. Glioblastoma is a type of astrocytoma that tends to grow very quickly. It is also the most common type of malignant glioma.

• Brain stem glioma. This kind of glioma starts in the brain stem. It's more common in children than in adults. Because the brain stem controls many important functions, such as breathing and heart rate, this kind of tumor usually can’t be removed by surgery.

• Ependymoma. This kind of tumor starts in cells that line the fluid-filled spaces within the brain. These spaces are called ventricles. The tumor doesn’t often grow into nearby brain tissue. This means in some cases it can be cured with surgery.

• Oligodendroglioma. This kind of tumor starts in cells that make myelin, the fatty substance that surrounds nerves. Like an astrocytoma, this tumor tends to spread into nearby brain tissue and is often hard to cure with surgery. 

• Optic nerve glioma. This rare glioma is most common in children. It's linked to a syndrome called NF1 (neurofibromatosis type 1). The tumor grows in or around the nerve that sends messages from the eyes to the brain. This can cause vision changes. It can also cause hormone changes because it's close to the pituitary gland. 

Other types of primary tumors include:

• Embryonal tumor or primitive neuroectodermal tumor.  This kind of tumor grows more often in young children. It can start anywhere in the brain in early forms of nerve cells. The most common type is medulloblastoma. It starts in the cerebellum. These tumors tend to grow and spread quickly. 

• Tumor of the pineal gland. This rare tumor starts in the pineal gland. This is a tiny organ near the center of the brain. The tumor can be fast-growing, called pineoblastoma. It's most common in children and linked with an inherited change in the RB1 (retinoblastoma) gene.

• Pituitary tumor. This kind of tumor starts in the pituitary gland at the base of the brain. It's almost never cancer. Still, it can cause serious symptoms because of its location and because it may make too many hormones. 

• Craniopharyngioma. This kind of tumor starts near the pituitary gland. It usually occurs in children and is often slow growing. But it can cause symptoms if it presses on the pituitary gland or on nearby nerves. 

• Schwannoma. This kind of tumor starts in myelin-making cells that surround certain nerves. These are called Schwann cells. The tumor can start in the vestibular nerve in the inner ear that helps with balance. If it grows there, the tumor is called a vestibular schwannoma or an acoustic neuroma. This type of tumor is usually not cancer. 

• Meningioma. This kind of tumor starts in the outer linings of the brain (meninges). It's the most common type of primary brain tumor in adults. Fortunately, it is usually a benign tumor. This means that while it can grow large, it does not spread (or metastasize). Many meningiomas can be removed with surgery, but some may grow back.  

• Primary central nervous system lymphoma. This is an aggressive, rare type of tumor that starts in lymphocytes. This is a type of immune cell. The tumor is common in people with a disease of the immune system, such as AIDS. But new HIV treatments have made it less common.

A secondary brain tumor is also known as a metastatic brain tumor. This is cancer that starts in another part of the body and then travels to the brain. In adults, secondary brain tumors are 10 times more common than primary brain tumors. 

Cancer in the brain that has spread from another part of the body is not brain cancer. It's still the same type of cancer as where it started. For instance, lung cancer that has spread to the brain is called metastatic lung cancer, not brain cancer. The cancer cells in the brain look like, act like, and are treated like the cancer cells in the lung. These are some of the most common types of cancer that spread to the brain:

• Lung cancer

• Breast cancer

• Melanoma

• Colon cancer

• Kidney cancer

• Nasopharyngeal cancer

If you have questions about brain tumors, talk with your healthcare provider. Your healthcare provider can help you understand more about this condition.