Brain Tumors in Adults

The central nervous system

To understand brain and spinal cord tumors, it helps to know about the normal structure and function of the central nervous system (CNS), which includes the brain and spinal cord. Together, they control how we think, feel, move, and sense the world around us.

• The brain is in charge of thought, memory, emotions, speech, vision, hearing, breathing, movement, and much more.
• The spinal cord connects the brain to the rest of the body. Along with special head nerves called cranial nerves, it carries messages back and forth. These messages tell muscles how to move, bring in signals from our senses, and help control our organs.

Both the brain and spinal cord are well protected, the brain by the skull and the spinal cord by the bones of the spine (vertebrae).

They are also cushioned by a clear liquid called cerebrospinal fluid (CSF). This fluid is made in small structures called the choroid plexus, which sit inside spaces in the brain called ventricles. The ventricles and the spaces around the brain and spinal cord are filled with CSF.

Main parts of the brain

The brain has 3 main areas, each with a special job:

• Cerebrum: The large, upper part of the brain, which is split into left and right halves. It controls thinking, memory, emotions, language, and voluntary movements (like walking, chewing, or throwing a ball). It also processes information from senses like sight, sound, smell, touch, and pain.
• Cerebellum: Located at the back of the brain, below the cerebrum. It helps coordinate balance and movement.
• Brain stem: The lower part of the brain that connects to the spinal cord. It controls basic life functions like breathing and heartbeat. It also carries signals between the brain and the rest of the body. The brain stem has 3 parts: the midbrain, pons, and medulla. Because the brain stem is small but vital, surgery in this area can be very risky.

Cranial nerves

The cranial nerves extend directly from the brain (as opposed to coming out of the spinal cord). They control movement and sensation in the face, eyes, ears, tongue, and some other areas.

Spinal cord

The spinal cord is a long bundle of nerves inside the spine. It carries signals between the brain and the rest of the body related to movement, sensation, and functions like bladder and bowel control.

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. Together, they affect other glands in the body, which in turn influence things like growth, metabolism, sexual development, milk production, and water balance. Tumors or treatments in this area can cause hormone changes. If this happens, people may need to take medicine to replace the missing hormones.

For more on tumors that start in the pituitary, see Pituitary Tumors.

Pineal gland

The pineal gland is a small gland deep inside the brain. It’s part of the body’s hormone system and helps control sleep by making melatonin. Tumors here are rare, but one type is called a pineoblastoma.

Blood-brain barrier

This is a protective layer around the brain’s blood vessels. It helps keep toxins and some other substances in the blood from getting into the brain. Unfortunately, it can also stop many chemotherapy drugs from reaching brain tumors.

Choroid plexus

This is the area of the brain within the ventricles that makes cerebrospinal fluid (CSF), which cushions and nourishes the brain.

Cells and tissues in the brain and spinal cord

The brain and spinal cord are made up of many kinds of cells and tissues. These can develop into different types of tumors.

Neurons (nerve cells): These are the “working” cells in the brain. They control thought, memory, emotion, speech, muscle movement, and sensation, and many other body functions.

Unlike most other types of cells in the body, most neurons in the brain and spinal cord stop dividing about a year after birth, so they rarely form tumors. But neurons can be damaged by tumors that start near them.

Glial cells: Glial cells are the “helper” cells of the brain. Most brain and spinal cord tumors start in glial cells. As a group, these tumors are called gliomas.

There are 3 main types of glial cells:

• Astrocytes support and nourish neurons. They also form scar tissue when the brain is injured. Most tumors starting in these cells are called astrocytomas or glioblastomas.
• Oligodendrocytes make myelin, a fatty coating that insulates nerve fibers and helps signals travel through neurons. Tumors starting in these cells are called oligodendrogliomas.
• Ependymal cells line the ventricles (fluid-filled areas) within the brain and form part of the pathway through which CSF flows. Tumors starting in these cells are called ependymomas.

A fourth type of cell, called microglia, are the infection-fighting cells of the central nervous system. They are part of the immune system, so they’re not truly glial cells, and they rarely form tumors.

Neuroectodermal cells: Also known as primitive neuroepithelial cells, these are early “starter” cells that help form the nervous system during development. They are found throughout the brain, although they are not often seen in the adult central nervous system. The most common tumors that come from these cells develop in the cerebellum and are called medulloblastomas.

Meninges: These are thin layers of tissue that cover and protect the brain and spinal cord. Tumors that start in these tissues are called meningiomas. In adults, they’re among the most common tumors that affect the brain, even though they’re not technically brain tumors.