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Living with a Brain Tumor
Dr. Peter Black's Guide to Taking Control of Your Treatment
By Peter Black, Sharon Cloud Hogan
Henry Holt and CompanyCopyright © 2006 Peter Mclaren Black
All rights reserved.
What Is a Brain Tumor?
A brain tumor is a mass of abnormal cells growing in the brain. The cells can come from the brain itself, from its lining, or from other places in the body. Brain tumors that develop in the brain itself (from brain cells, blood vessels, nerves, or membranes covering the brain) are called primary brain tumors. They may be benign or malignant. Benign brain tumors grow slowly and do not invade brain tissue; examples are meningiomas, vestibular schwannomas, and pituitary adenomas. They still pose a threat to health because they may put pressure on important areas of the brain. Malignant primary brain tumors spread into the healthy tissues that surround them and tend to grow more quickly than benign tumors. They are difficult to treat because they spread into the brain like alien invaders in a population of normal citizens.
Brain tumors that spread from cancer elsewhere in the body (such as skin, breast, lung, or colon cancer) are secondary or metastatic brain tumors. They are all malignant.
What Causes a Brain Tumor? Why Me?
If you or your friend or family member has been diagnosed with a brain tumor, you may ask what you did wrong to deserve it. It's important to remember that a brain tumor is not your fault. In most cases, it's random — something we don't know how to prevent. It's not your cell phone. It's not because of something you ate or didn't eat. It's not a punishment for something that you may have done in the past. Although we know some factors that are associated with brain tumors, altogether they account for fewer than 10 percent of the tumors we see. These factors include genes, radiation, and some chemicals. But in most cases, we simply don't understand what causes these tumors.
In this section I will discuss briefly what we do know about the factors associated with brain tumors. You might want to know that epidemiologists — researchers who investigate the incidence and control of disease in a given population — are working very hard to determine which environmental and other factors may set the stage for brain tumors. Their research will be increasingly important in the future.
Table 1-1 lists some genetic disorders that are associated with brain tumors.
Additional genetic factors may predispose certain people to cancer. Sixteen percent of patients with primary brain tumors have a family history of cancer. This has led to the concept of cancer susceptibility genes — genes that by themselves do not cause cancer but make it more likely that a cancer will develop. Scientists are presently sorting out what these genes are and how they cause tumors.
Past radiation to the head and neck may cause astrocytomas, meningiomas, and some other tumors. These "radiation-induced" tumors occur five to twenty years after the original irradiation; we think they occur because of DNA damage sustained during prolonged radiation therapy. There is no evidence that the small amounts of radiation from diagnostic x-rays cause brain tumors.
Chemical Exposure and Diet
Exposure to certain chemicals such as vinyl chloride, N-nitrosourea compounds, and some pesticides (which are no longer on the market) may lead to astrocytomas. Tobacco, alcohol, and diet have not been directly associated with brain tumors.
Some researchers and patients have raised concerns about a link between brain tumors and the electromagnetic fields (EMFs) surrounding cell phones or high-tension wires. Several recent studies have shown no such correlation.
There is no convincing evidence that head trauma causes brain tumors.
How Does a Brain Tumor Develop?
A brain tumor appears to come from one abnormal brain cell that grows when it is not supposed to. At least five changes allow it to develop. One change is that the cell learns to stimulate its own growth by producing growth factors that encourage its division. These growth factors are the product of genes called oncogenes. When they are turned on in the cell, they stimulate growth of that cell and the cells around it. We don't know why these genes are turned on, however.
A second change is that a tumor cell may lose "tumor suppressor genes." The cell uses these genes to divide during development, but then they normally are turned off. An example is the gene called merlin that is lost or defective in a condition called neurofibromatosis; as a result of this, cells continue to grow.
Third, malignant tumor cells learn to spread into the brain by dissolving the matrix of brain tissue and traveling through it; this process is called invasion.
Fourth, primary malignant tumors may hide themselves from the normal immune cells of the brain by coating themselves with molecules that make them invisible.
Last, malignant tumors may form new blood vessels in order to increase their own nutrient supply and enhance growth. This process is called angiogenesis.
Our understanding of these possible causes of brain tumor growth is important because it may help us to treat brain tumors by blocking growth factors with "smart" drugs, by replacing defective tumor suppressor genes with gene therapy, by preventing invasion, by enhancing the immune response, or by blocking new blood vessel formation. We will discuss all of these new therapies in chapter 14.
What Does a Brain Tumor Do to the Brain?
If the human brain were so simple that we could understand it, we would be so simple that we couldn't.
— Scientist Emerson M. Pugh
Now that we've run through the mechanics of brain tumors, let's take a look at how they affect the brain. The first step is to give you a brief anatomy lesson about the brain, its component parts and what they do, so you can understand how a tumor affects the way a normal brain functions. Some parts of your body can expand and contract because only skin covers them. The enlarging waist is a problem for your clothes, but not for your body. The brain is different because it lives inside the skull and the skull cannot enlarge to accommodate anything more than the structures it already houses: the brain, cerebrospinal fluid, and blood vessels. A brain tumor is a mass that is an unwelcome addition that presses on important brain parts. Here is an introduction to these parts and what they do.
Where it is: The cerebrum, the largest part of your brain, occupies the upper two-thirds of your head. It contains a right and a left hemisphere connected by the corpus callosum, which sends messages from one side of the brain to the other. The cerebrum also contains the basal ganglia, thalamus, and lateral and third ventricles.
What it's made of: Most of the cerebrum is made up of glial cells (astrocytes, oligodendrocytes, or ependymal cells), whose functions are poorly understood. About 5 percent of cerebral cells are neurons, which transmit nerve impulses. These cells make up the gray matter, the outer part of the brain. The central part of the cerebrum is composed of fibers that connect the cerebrum to the rest of the brain. There are four lobes in the cerebrum: frontal, parietal, temporal, and occipital (see figure 1).
What happens there: The cerebrum is the source of conscious activity. It controls sensation, movement, hearing, and vision. The right hemisphere directs the left side of the body and the left hemisphere controls the right side.
Where it is: Your frontal lobe begins just behind your forehead and extends halfway back in your skull.
What happens there: The frontal lobe contributes to bodily movement, speech, decision making, planning, reasoning, personality, creativity, mood, and inhibition.
Where it is: The parietal lobe sits at the top of your head, behind the frontal lobe.
What happens there: The parietal lobe controls your sense of touch and some of your visual capacity, including your ability to recognize what you see.
Where it is: Your temporal lobe is below your frontal and parietal lobes, just above your ear.
What happens there: This part of your brain is important in hearing and may also affect speech, behavior, emotions, and memory.
Where it is: The occipital lobe is located in the back of your head.
What happens there: This part of the brain is important in vision.
Where they are: Deep inside the cerebrum are the "great lakes" of the brain — four cerebral ventricles that form the brain's ventricular system. These ventricles are filled with a clear liquid called cerebrospinal fluid (CSF) in which the brain floats. Sometimes a brain tumor blocks the flow of CSF and these "lakes" overflow — this condition, called hydrocephalus, can be life-threatening.
Where they are: The basal ganglia include the putamen and the globus pallidus. They are deep inside the cerebrum and form the walls of the lateral ventricles.
What they do: The basal ganglia are important in the smoothness of movement.
Where it is: The thalamus (see figure 2) is located at the center of your brain, around the third ventricle.
What happens there: Your thalamus serves as a relay station for sensation and movement.
Where it is: The hypothalamus is located deep inside your brain, where it forms the lower wall of the third ventricle.
What happens there: Your hypothalamus regulates your body temperature and hormones. It affects your hunger, thirst, moods, motivation, and sexual development.
Where it is: Your pituitary is a small gland the size of a cherry enclosed in the bony sella turcica (which translates as "Turkish saddle") at the base of the brain. It is connected to your hypothalamus and is composed of two lobes: the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis).
What happens there: The pituitary gland is a master hormonal gland that controls the thyroid and adrenal glands and the sexual organs. It also controls water balance in the body.
Where it is: The cerebellum is the second largest part of your brain. It is located in the back of your head just above your neck, and it covers the brain stem at the base of your brain. Like the cerebrum, the cerebellum has two hemispheres; the right cerebellum controls the right side of the body.
What happens there: Your cerebellum controls your balance, coordination, and fine-muscle movement. There is increasing evidence that it has cognitive effects as well.
Where it is: The brain stem is at the base of the brain, protected by the cerebrum and cerebellum. This part of your brain, which is composed of the midbrain, pons, and medulla oblongata, connects the cerebrum to the spinal cord.
What happens there: Your vital physical functions like breathing, eye movements, swallowing, heartbeat, and blood pressure are all controlled from the brain stem. In particular, the reticular formation is responsible for consciousness and patterns of sleeping and eating. The midbrain is related to hearing and sight. The pons conveys impulses between the largest parts of your brain — the cerebrum and cerebellum — and your spinal cord.
Where it is: This gland is just beneath the corpus callosum, behind the third ventricle.
What happens there: Your pineal gland regulates sleep and other body rhythms.
Where they are: Three sheets of tissue called the meninges surround the brain. The first of these sheets is the pia, which tightly surrounds the cerebrum and cerebellum. The second is the arachnoid, which is more loosely connected to the skull and contains CSF. The third is the dura, a very tough outer layer that is tightly connected to the skull.
What happens there: The dura divides the brain compartments into three sections — the falx separates the right and left hemispheres of the cerebrum and the tentorium separates the cerebrum from the cerebellum. The dura also has several large venous channels called sinuses, which are important exit routes for blood. Meningiomas are brain tumors that grow from the meninges.
Cranial nerves (see figure 3) connect your brain to the sensation and movement components of your face. Here is a table of their names and functions:
Other Terms You May Hear
Blood brain barrier. A mechanism by which the blood vessels of the brain filter out and prevent substances in the blood from reaching the brain. This protects the brain from the chemicals in the blood.
Descending tract. Nerves that descend from the brain to the spinal cord.
Glia. Most of the tissue of the brain is composed of glial cells. These cells may be either astrocytes, star-shaped cells that are crucial to metabolism in the brain; oligodendrocytes, which maintain myelin over the nerve cells and help them communicate with each other; or ependymal cells, which line the ventricles of the brain. Most brain tumors originate from glial cells.
Tentorium. The tentorium is a flap of dura that creates a sort of horizontal dividing line between the top and bottom of the brain. The upper area above the tentorium (which includes the cerebral hemispheres) is called the supratentorial compartment. Most brain tumors in adults are supratentorial. The bottom section of the brain, which is made up of both the cerebellum and the brain stem, is called the infratentorial compartment (or posterior fossa). Most brain tumors in children are infratentorial.
Cranium. Another word for the skull. The cranium includes the ethnoid, frontal, sphenoid, temporal, parietal, and occipital bones.
Skull base. The bones at the bottom of the skull, beneath the frontal and temporal lobes, the cerebellum, and the brain stem.
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Now that you know what a brain tumor is, how it grows, and what it does to the brain, let's move on to chapter 2, where I will explain how we diagnose brain tumors.CHAPTER 2
How Brain Tumors Are Diagnosed
Our son kept sitting closer and closer to the TV. We thought it was just his prescription for glasses — how did we know it was a brain tumor pressing on his optic nerves?
— Mother of a child with a brain tumor
I hit my head and had a CT scan — the next thing I knew a doctor was telling me I had a brain tumor. How weird is that?
— Brain tumor patient
He was fine and then he wasn't fine.
— Father of a child with a brain tumor
In the early twentieth century, a doctor named Harvey Cushing started the surgical specialty of neurosurgery. Working at the Peter Bent Brigham Hospital in Boston, Cushing demonstrated that a neurosurgeon could operate on brain tumors safely. At that time, the only way to diagnose brain tumors was to listen to a patient's story, do a physical examination, and evaluate skull x-ray films.
Excerpted from Living with a Brain Tumor by Peter Black, Sharon Cloud Hogan. Copyright © 2006 Peter Mclaren Black. Excerpted by permission of Henry Holt and Company.
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