Anatomy of the Human Brain

The image on the left is a side view of the outside of the brain, showing the major lobes (frontal, parietal, temporal and occipital) and the brain stem structures (pons, medulla oblongata and cerebellum).

The image on the right is a side view showing the location of the limbic system inside the brain. The limbic system consists of a number of structures, including the fornix, hippocampus, cingulate gyrus, amygdala, the parahippocampal gyrus and parts of the thalamus. The hippocampus is one of the first areas affected by Alzheimer's disease. As the disease progresses, damage extends throughout the lobes.

Glossary of Terms for an Anatomy of the Brain

Amygdala – limbic structure involved in many brain functions, including emotion, learning and memory. It is part of a system that processes "reflexive" emotions like fear and anxiety.

Cerebellum – governs movement.

Cingulate gyrus – plays a role in processing conscious emotional experience.

Fornix – an arch-like structure that connects the hippocampus to other parts of the limbic system.

Frontal lobe – helps control skilled muscle movements, mood, planning for the future, setting goals and judging priorities.

Hippocampus – plays a significant role in the formation of long-term memories.

Medulla oblongata – contains centers for the control of vital processes such as heart rate, respiration, blood pressure, and swallowing.

Limbic system – a group of interconnected structures that mediate emotions, learning and memory.

Occipital lobe – helps process visual information.

Parahippocampal gyrus – an important connecting pathway of the limbic system.

Parietal lobe – receives and processes information about temperature, taste, touch, and movement coming from the rest of the body. Reading and arithmetic are also processed in this region.

Pons – contains centers for the control of vital processes, including respiration and cardiovascular functions. It also is involved in the coordination of eye movements and balance.

Temporal lobe – processes hearing, memory and language functions.

Thalamus – a major relay station between the senses and the cortex (the outer layer of the brain consisting of the parietal, occipital, frontal and temporal lobes).

Types of Brain Tumors

There are many different types of brain tumors. They are usually categorized by the type of cell where the tumor begins, or they are also categorized by the area of the brain where they occur. The most common types of brain tumors include the following:

Gliomas
The most common type of primary brain tumor is a glioma. Gliomas begin from glial cells, which are the supportive tissue of the brain. There are several types of gliomas, categorized by where they are found, and the type of cells that originated the tumor. The following are the different types of gliomas:

• Astrocytomas
  Astrocytomas are glial cell tumors that are derived from connective tissue cells called astrocytes. These cells can be found anywhere in the brain or spinal cord. Astrocytomas are the most common type of childhood brain tumor, and the most common type of primary brain tumor in adults. Astrocytomas are generally subdivided into high-grade or low-grade tumors. High-grade astrocytomas are the most malignant of all brain tumors. Astrocytomas are further classified for presenting signs, symptoms, treatment, and prognosis, based on the location of the tumor. The most common location of these tumors in children is in the cerebellum, where they are called cerebellar astrocytomas. These persons usually have symptoms of increased intracranial pressure, headache, and vomiting. There can also be problems with walking and coordination, as well as double vision. In adults, astrocytomas are more common in the cerebral hemispheres (cerebrum), where they commonly cause increased intracranial pressure (ICP), seizures, or changes in behavior.


• Brain stem gliomas
  Brain stem gliomas are tumors found in the brain stem. Most brain stem tumors cannot be surgically removed because of the remote location and delicate and complex function this area controls. Brain stem gliomas occur almost exclusively in children; the group most often affected is the school-age child. The child usually does not have increased intracranial pressure (ICP), but may have problems with double vision, movement of the face or one side of the body, or difficulty with walking and coordination.


• Ependymomas
  Ependymomas are also glial cell tumors. They usually develop in the lining of the ventricles or in the spinal cord. The most common place they are found in children is near the cerebellum. The tumor often blocks the flow of the CSF (cerebral spinal fluid, which bathes the brain and spinal cord), causing increased intracranial pressure. This type of tumor mostly occurs in children younger than 10 years of age. Ependymomas can be slow growing, compared to other brain tumors, but may recur after treatment is completed. Recurrence of ependymomas results in a more invasive tumor with more resistance to treatment.


• Optic nerve gliomas
  Optic nerve gliomas are found in or around the nerves that send messages from the eyes to the brain. They are frequently found in persons who have neurofibromatosis, a condition a child is born with that makes him/her more likely to develop tumors in the brain. Persons usually experience loss of vision, as well as hormone problems, since these tumors are usually located at the base of the brain where hormonal control is located. These are typically difficult to treat due to the surrounding sensitive brain structures.


• Oligodendrogliomas
  This type of tumor also arises from the supporting cells of the brain. They are found commonly in the cerebral hemispheres (cerebrum). Seizures are a very common symptom of these tumors, as well as headache, weakness, or changes in behavior or sleepiness. This tumor is more common in persons in their 40s and 50s. These tumors have a better prognosis than most other gliomas, but they can become more malignant with time.

Metastatic tumors
In adults, metastatic brain tumors are the most common type of brain tumors. These are tumors that begin to grow in another part of the body, then spread to the brain through the bloodstream. When the tumors spread to the brain, they commonly go to the part of the brain called the cerebral hemispheres, or to the cerebellum. Often, a patient may have multiple metastatic tumors in several different areas of the brain. Lung, breast, and colon cancers frequently travel to the brain, as do certain skin cancers. Metastatic brain tumors may be quite aggressive and may return even after surgery, radiation therapy, and chemotherapy.

Meningiomas
Meningiomas are usually benign tumors that come from the meninges or dura, which is the tough outer covering of the brain just under the skull. This type of tumor accounts for about 15 percent of brain tumors. They are slow growing and may exist for years before being detected. Meningiomas are most common in patients in their 40s and 50s. They are commonly found in the cerebral hemispheres just under the skull. They usually are separate from the brain and can sometimes be removed entirely during surgery. They can, however, recur after surgery and certain types can be malignant.

Schwannomas
Schwannomas are benign tumors, similar to meningiomas. They arise from the supporting cells of the nerves leaving the brain, and are most common on the nerves that control hearing and balance. When schwannomas involve these nerves, they are called vestibular schwannomas or acoustic neuromas. Commonly, they present with loss of hearing, and occasionally loss of balance, or problems with weakness on one side of the face. Surgery can be difficult because of the area of the brain in which they occur, and the vital structures around the tumor. Occasionally, radiation (or a combination of surgery and radiation) is used to treat these tumors.

Pituitary tumors
The pituitary gland is a gland located at the base of the brain. It produces hormones that control many other glands in the body. These glands include the thyroid gland, the adrenal glands, the ovaries and testes, as well as milk production by pregnant women, and fluid balance by the kidney. Tumors that occur in or around the area of the pituitary gland can affect the functioning of the gland, or overproduce hormones that are sent to the other glands. This can lead to problems with thyroid functioning, impotence, milk production from the breasts, irregular menstrual periods, or problems regulating the fluid balance in the body. In addition, due to the closeness of the pituitary to the nerves to the eyes, patients may have decreased vision. Tumors in the pituitary are frequently benign, and total removal makes the tumors less likely to recur. Since the pituitary is at the base of the skull, approaches for removal of a pituitary tumor may involve entry through the nose or the upper gum. Certain types of tumors may be treated with medication, which, in some cases, can shrink the tumor or stop the growth of the tumor.

Primitive neuroectodermal tumors (PNET)
PNET can occur anywhere in the brain, although the most common place is in the back of the brain near the cerebellum. When they occur here, they are called medulloblastomas. The symptoms depend on their location in the brain, but typically the patient experiences increased intracranial pressure. These tumors are fast growing and often malignant, with occasional spreading throughout the brain or spinal cord.

Medulloblastomas
Medulloblastomas are one type of PNET that are found near the midline of the cerebellum. This tumor is rapidly growing and often blocks drainage of the CSF (cerebral spinal fluid, which bathes the brain and spinal cord), causing symptoms associated with increased ICP. Medulloblastoma cells can spread (metastasize) to other areas of the central nervous system, especially around the spinal cord. A combination of surgery, radiation, and chemotherapy is usually necessary to control these tumors.

Craniopharyngioma
Craniopharyngioma are benign tumors that occur at the base of the brain near the nerves from the eyes to the brain, and the hormone centers. Most persons with this type of brain tumor develop symptoms before the age of 20. Symptoms include headaches, as well as problems with vision. Hormonal imbalances are common, including poor growth and short stature. Symptoms of increased intracranial pressure may also be seen. Although these tumors are benign, they are hard to remove due to the sensitive brain structures that surround them.

Pineal region tumors
Many different tumors can arise near the pineal gland, a gland that helps control sleep and wake cycles. Gliomas are common in this region, as are pineal blastomas. In addition, germ cell tumors, another form of malignant tumor, can be found in this area. Tumors in this region are more common in children than adults, and make up 3 to 8 percent of pediatric brain tumors. Benign pineal gland cysts are also seen in this location, which makes the diagnosis difficult between what is malignant and what is benign. Biopsy or removal of the tumor is frequently necessary to tell the different types of tumors apart. Persons with tumors in this region frequently experience headaches or symptoms of increased intracranial pressure. Treatment depends on the tumor type and size.

What is Brain Cancer?

Brain cancers are abnormal growths of tissue found inside the skull. The brain is a soft spongy mass of nerve cells and supporting tissue. It controls every physiological system in the body and is responsible for our thoughts, language and emotions. In the brain, any abnormal growth puts pressure on sensitive structures and may impair their function. Tumors that occur in the brain may be either benign (non-cancerous), or malignant (cancerous). Benign brain tumors do not contain cancer cells or invade other tissue, but they can cause pressure in areas of the brain and cause symptoms. Malignant tumors that start in any tissue of the brain are classified as primary brain cancer or brain cancer. Primary brain cancer rarely metastasizes (spreads) to other parts of the body. Cancer that starts in another part of the body and metastasizes to the brain is classified as secondary brain cancer or metastatic brain cancer. Primary brain cancer and secondary brain cancer are usually treated differently.

There are two types of brain tumors: primary brain tumors that originate in the brain and metastatic (secondary) brain tumors that originate from cancer cells that have migrated from other parts of the body. Doctors classify primary brain tumors according to the type of brain cells they develop from, the appearance of individual cells under the microscope, their location in the brain, or a combination of these factors. More than half of adult brain tumors are gliomas, which means they arise in the tissue in the brain known as glial tissue. Examples include astrocytomas, which start in brain cells called astrocytes, and glioblastomas, which are particularly aggressive forms of astrocytomas.

Like any cancer, brain cancer gets its start when cells start dividing abnormally and uncontrollably, forming growths known as tumors. But not all tumors are cancerous. Some are benign, meaning that they are caused by overgrowth of normal cells. Benign tumors tend to grow slowly and don't spread, or metastasize, in the same way that malignant tumors do. Still, benign tumors in the brain or spinal cord can pose a threat to health because they can compress and destroy adjacent vital tissue or increase pressure in the skull. Cancerous tumors in the brain typically don't spread to distant areas of the body, but they can invade other areas of the brain and the spinal cord.

Cancers that start in the brain are called primary brain cancers. Cancers that start in another part of the body and spread to the brain are called secondary brain cancers or metastatic brain cancer. These are much more common than primary brain tumors. Metastatic brain cancer most often spreads from the lung, breast, kidney, and skin (melanoma). Brain cancers are generally named after the tissue in which they arise. Majority are glima arising from glial cells in the brain. These include astrocytomas, oligodenrogliomas, ependymomas and mixed cell type gliomas. The other forms of brain cancers are meningiomas, medulloblastomas, chordomas and central nervious system lymphomas.

Brain cancers can be fast growing (high grade), such as glioblastoma multiforme or slow growing (low grade), such as pilocytic astrocytoma. Cancers from other organs can spread to the brain and are called brain metastases. Brain metastases comprise cancer cells from the original site of cancer, such as lung cancer cells and breast cancer cells.

Brain cancer is not very common, and unlike many other cancers, does not usually spread to other parts of the body. Since the brain controls learning, memory, senses (hearing, visual, smell, taste, touch), emotions, muscles, organs, and blood vessels, all cancerous brain tumors are life threatening.

Causes of Brain Cancer

Genetic factors, various environmental toxins, radiation, and cigarette smoking have all been linked to cancers of the brain, but in most cases, no clear cause can be shown. Brain cancer is a malignant growth (tumor) in the brain. The majority of brain tumors have abnormalities of genes involved in cell cycle control, causing uncontrolled cell growth. These abnormalities are caused by alterations directly in the genes, or by chromosome rearrangements which change the function of a gene.

Patients with certain genetic conditions (i.e., neurofibromatosis, von Hippel-Lindau disease, Li-Frameni syndrome, and retinoblastoma) also have an increased risk to develop tumors of the central nervous system. There have also been some reports of people in the same family developing brain tumors who do not have any of these genetic syndromes. Some chemicals may change the structure of a gene that protects the body from diseases and cancer. Workers in oil refining, rubber manufacturing, and chemists have a higher incidence of certain types of tumors. Which, if any, chemical toxin is related to this increase in tumors is unknown at this time. Patients who have received radiation therapy to the head as part of prior treatment for other malignancies are also at an increased risk for new brain tumors.

Symptoms of Brain Cancer

Brain cancer symptoms may vary from person to person. Whether a brain cancer is detected early usually depends on its location within the brain. Cancers located in more important areas of the brain may cause symptoms earlier than those located in less important areas of the brain. Brain and spinal cord tumors often interfere with the specific functions of the region they develop in. For example, spinal cord tumors often cause numbness and/or weakness of both legs, and tumors of the basal ganglia typically cause abnormal movements and abnormal positioning of the body.

Tumors within any part of the brain may cause pressure to rise within the skull. Increased pressure within the skull may cause headache, nausea, vomiting, or blurred vision. Headache is probably the most common symptom of a brain tumor. It should be strongly emphasized, however, that most headaches do not represent an underlying brain tumor. None of these symptoms are specific for brain or spinal cord cancer and they all may be caused by other disorders. Less than 1% of headaches are caused by brain cancer. Approximately 10% of new onset seizures in adults are caused by brain tumors. Seizures occur in between 15% and 95% of patients, depending on the location of the tumor. Tumors are more likely to be localized and affect one area of the brain. In such cases they can cause partial seizures . In this case, a person does not lose consciousness but may experience confusion, jerking movements, tingling, or odd mental and emotional events. Generalized seizures , which can cause loss of consciousness, are less common, since they are caused by disturbances of nerve cells in diffuse areas of the brain.

Gastrointestinal symptoms, including nausea, are also common. Nausea and vomiting, in fact, often occur in children with brain tumors and in all people with brain stem cell tumors. Sometimes the only symptoms are mental changes, which may include memory loss, impaired concentration, problems with speech and reasoning, and increased sleep.

Tests to Diagnose

The initial test is an interview and physical examination of the person by a competent health-care provider. The results of this interaction will determine if other specific tests need to be done.

The most frequently used test to detect brain cancer is a CAT scan (computed automated tomography or CT). This test resembles a series of x-rays and is not painful, although sometimes a dye needs to be injected into the vein for better pictures of some internal brain structures. Another test that is gaining popularity because of its high sensitivity for detecting anatomic changes in the brain is MRI (magnetic resonance imaging). This test also resembles a series of x-rays and shows the brain structures in detail better than CT. MRI is not as widely available as CT scanning. If the tests show evidence (tumors or abnormalities in the brain tissue) of brain cancer, then other doctors such as neurosurgeons and neurologists that specialize in treating brain ailments will be consulted to help determine what should be done to treat the patient. Other tests (white blood cell counts, electrolytes, etc.) are likely to be ordered by the health-care giver to help determine the patient's state of health or to detect other health problems.

Brain Cancer Treatment

A treatment plan is individualized for each brain cancer patient. The treatment plan is constructed by the doctors who specialize in brain cancer, and treatments vary widely depending on the cancer type, brain location, tumor size, patient age, and patient's general health status. A major part of the plan is also determined by the patient's wishes. Patients should discuss treatment options with their health-care providers.

Surgery, radiation therapy, and chemotherapy are the major treatment categories for most brain cancers. Individual treatment plans often include a combination of these treatments. Surgical therapy attempts to remove the tumor by cutting it away from normal brain tissue. Radiation therapy attempts to destroy tumor cells by using high energy radiation focused onto the tumor. Chemotherapy attempts to destroy tumor cells using chemicals (drugs) that are designed to destroy specific types of cancer cells. All treatments attempt to spare normal brain cells.

Other treatments that may be part of some treatment plans may include hyperthermia (heat treatments), immunotherapy (immune cells directed to kill certain cancer cell types), or steroids to reduce inflammation and brain swelling. Clinical trials (treatment plans designed by scientists to try new chemicals or methods on patients) can be another way for patients to obtain treatment specifically for their cancer cell type.

The best treatment for brain cancer is designed by the team of cancer specialists in conjunction with the wishes of the patient.

Side Effects of Brain Cancer Treatment

Side effects of brain cancer treatment vary with the treatment plan and the patient. Most treatment plans try to keep all side effects to a minimum. For some patients, the side effects of brain cancer treatment can be severe. Treatment plans should include a discussion of potential side effects and the likelihood of them developing, so the patient and their caregivers (family, friends) can make appropriate treatment decisions in conjunction with their medical team. Also, if side effects develop, the patient has some knowledge of what to do about them such as when to take certain medicines or when to call their doctor to report health changes.

Surgical side effects include an increase in current symptoms, damage to normal brain tissue, brain swelling, and seizures. Other changes in brain functions such as muscle weakness, mental changes, and decreases in any brain-controlled function can occur. Combinations of these side effects may happen. The side effects are most noticeable shortly after surgery but frequently decline with time. Occasionally, the side effects do not decline.

Chemotherapy usually affects (kills) rapidly growing cancer cells but also can affect normal tissue. Chemotherapy is usually given intravenously so the drugs can reach most body organs. Common side effects of chemotherapy are nausea, vomiting, hair loss, and loss of energy. The immune system is often is depressed by chemotherapy, which results in a high susceptibility to infections. Other systems, such as the kidneys and the reproductive organs, may also be damaged by chemotherapy. Most of the side effects decline over time, but some may not.

Radiation therapy has most of the same side effects as chemotherapy. Most radiation therapy is focused onto the brain cancer tissue, so some systems do not receive direct radiation (immune system, kidneys, and others). The effects on systems not receiving the direct radiation are usually not as severe as those seen with chemotherapy. However, hair and skin are usually affected, resulting in hair loss (sometimes permanently) and reddish and darkened skin that needs protection from the sun.