Brain and Spinal Cord Tumors in Children

Brain tumors are masses of abnormal cells that have grown out-of-control. In most other parts of the body, it is critically important to distinguish benign (noncancerous) tumors from malignant (cancerous) ones. Benign tumors are almost never life threatening. The main reason cancers are so dangerous is because they can spread throughout the body. Most brain cancers can spread through the brain tissue but rarely spread to other areas of the body. Even so-called “benign” tumors are can, as they grow, compress brain tissue, causing damage that is often disabling and sometimes fatal. For this reason, doctors usually speak of "brain tumors" rather than "brain cancers." The major distinction is how readily they spread through the rest of the brain central nervous system and whether they can be removed and not come back.

The central nervous system is the medical name for the brain and spinal cord. Central nervous system tumors of adults and children often form in different areas, develop from different cell types, and may have a different outlook and treatment. This document refers to children's tumors.

The brain is the center of thought, feeling, memory, speech, vision, hearing, movement, and much more. The spinal cord and special nerves in the head called cranial nerves carry messages between the brain and the rest of the body. These messages tell our muscles how to move, transmit information gathered by our senses, and help coordinate our internal organs. The brain is located within and protected by the skull. Likewise, the spinal cord is protected by the bones of the spinal column. The brain and spinal cord are surrounded and cushioned by a special fluid, called cerebrospinal fluid. Cerebrospinal fluid is produced by the choroid plexus, which is located in cavities within the brain called ventricles. The ventricles as well as the spaces around the brain and spinal cord are filled with cerebrospinal fluid.

Parts of the Brain and Spinal Cord

The brain and spinal cord are the 2 main parts of the central nervous system.

The main areas of the brain include the cerebral hemispheres, cerebellum, and brain stem. Each of these parts has a special purpose. Tumors of different parts of the central nervous system disrupt different functions and cause different symptoms. Any disease involving that particular location within the brain can cause these symptoms, and they do not necessarily mean a brain tumor is present. Also, tumors in different areas of the central nervous system may be treated differently and have a different prognosis (outlook for survival). In very young children, less than 3 years of age, itÂ’s often hard to tell which part of the brain is affected during its early development. Very young children may not have the usual symptomns coming from that part of the brain involved as would be seen in adults. In this age group the only symptoms may be nonspecific and include irritability, crying, poor feeding, or vomiting.

The 2 cerebral hemispheres control reasoning, thought, emotion, and language. They are also responsible for your planned muscle movements (throwing a ball, walking, chewing, etc.) and for taking in sensory information such as vision, hearing, smell, touch, and pain.

The symptoms caused by a tumor in a cerebral hemisphere depend on the part of the hemisphere in which the tumor arises. Common symptoms include:

* seizures
* trouble speaking
* a change of mood such as depression
* a change in personality
* numbness, weakness or paralysis of part of the body
* changes in vision, hearing, and sensation

The cerebellum controls coordination of movement. Tumors of the cerebellum cause difficulty with coordination in walking, difficulty with fine movements of arms and legs, and changes in rhythm of speech.

The brain stem contains bundles of very long nerve fibers (axons) that carry signals controlling muscles and sensation or feeling from the cerebrum to and from the rest the body. In addition, most cranial nerves (which carry signals to and from the face, eyes, tongue, and mouth) start in the brain stem. Special centers in the brain stem also control breathing and the beating of the heart.

Tumors in this critical area of the brain may cause weakness, stiff muscles, or problems with sensation, hearing, facial movement, and swallowing. Double vision is a common early symptom of brain stem tumors, as are problems with coordination in walking. Because tumors of the brain stem often intermingle with normal nerve cells and the brain stem is so essential for life, it may not be possible to surgically remove these tumors from the brain stem.

The spinal cord, like the brain stem, contains bundles of very long axons (wire-like extensions) that carry signals controlling muscles, sensation or feeling, and bladder and bowel control. Spinal cord tumors may cause weakness, paralysis, or numbness. Because the spinal cord is such a narrow structure, tumors arising within it usually cause symptoms involving both sides of the body (for example, weakness or numbness of both legs). This is different than tumors of the brain, which usually affect only one side of the body. Moreover, most tumors of the spinal cord arise below the neck after nerves to the arms have branched off the spinal cord, so that only lower body functions – bowel, bladder, or leg – are affected.

Tumors may also arise from cranial nerves. The most common cranial nerve tumor in children is optic glioma, a tumor of the optic nerve (the optic nerve is actually an extension of brain tissue to the eye) causing blindness. Tumors arising from other cranial nerves may cause hearing loss (acoustic nerve) in one or both ears, facial paralysis (facial nerve), or facial numbness or pain (trigeminal nerve). Tumors arising in the nerves of the peripheral nervous system (parts of the nervous system other than the brain and spinal cord) generally cause pain, weakness,and/or loss of sensation in the area served by that nerve. They can also weaken the muscles controlled by that nerve.

Types of Cells and Tissues in the Brain and Spinal Cord

The brain consists of different kinds of tissues and cells. Different types of tumors can start in these different cell and tissue types. These different types of tumors have varying outlooks for survival and may be treated differently.

Neurons: These are the most important cells within the brain. They send signals through the axons. Axons may be very short (in the brain) or 2 to 3 feet long (in the spinal cord). Electric signals carried by neurons determine thought, memory, emotion, speech, muscle movement, and just about everything else that the brain and spinal cord do. Unlike many other types of cells that can grow and divide to repair damage from injury or disease, neurons quit dividing about 1 year after birth (with a few exceptions). Neurons do not usually form tumors, but they are damaged by tumors that start nearby.

Glial cells: Most brain and spinal cord tumors develop from glial cells. There are 3 types of glial cells – astrocytes, oligodendrocytes, and ependymal cells. Tumors of glial cells are sometimes referred to as a group and called gliomas. A fourth cell type called microglia is part of the immune system and is not truly glial in origin. Normal glial cells grow and divide very slowly. Glial cells are the supporting cells of the brain and continue to increase in number until the child is 5 years of age. At this time, the brain reaches its maximum size and will be the same size throughout oneÂ’s lifetime.

* Astrocytes help support and nourish neurons. When the brain is injured, astrocytes form scar tissue that helps repair the damage.

* Oligodendrocytes make myelin, a substance that surrounds and insulates axons of the brain and spinal cord. This allows oligodendrocytes to help neurons transmit electric signals through axons.

* Ependymal cells line the ventricles within the central part of the brain and form part of the pathway through which cerebrospinal fluid travels.

* Microglia represent 10% to 20% of the total population of glial cells in the brain. They are the immune (infection fighting) cells of the central nervous system.

Neuroectodermal cells: These are primitive cells that are probably the remains of embryonic cells and are found throughout the brain. The most common tumor that comes from these cells is the medulloblastoma, which arises in the cerebellum.

Meninges: These are specialized tissues that line the cerebrospinal fluid-filled spaces surrounding the brain and spinal cord. The meninges help form the spaces through which cerebrospinal fluid travels.

Choroid plexus: The choroids plexus is the area of the brain within the ventricles that makes cerebrospinal fluid, which nourishes and protects the brain.

Pituitary gland and hypothalamus: The pituitary is a gland found at the base of the brain. The hypothalamus is a part of the brain next to the pituitary gland. Both of these tissues help regulate the activity of several other glands. For example, they control the production of thyroid hormone by the thyroid gland, the production and release of milk by the breasts, and the production of male or female hormones by the testicles or ovaries. They also produce growth hormone, which stimulates body growth, and vasopressin, which regulates water balance by the kidneys.

The growth of tumors in or near the pituitary or hypothalamus, as well as surgery and/or radiation therapy in this area, can interfere with these functions. Consequently, a child may have low levels of one or more hormones and may need hormone treatments to correct any hormone deficiency.

Pineal gland: The pineal gland is not strictly part of the brain. It is, in fact, an endocrine gland that sits between the cerebral hemispheres. Its function is probably to make melatonin, a hormone that responds to changes in light.

Blood-brain barrier: Unlike most other organs, there is a barrier between the blood and the tissues of the central nervous system (brain and spinal cord) that keeps many drugs from getting into the brain, including most chemotherapy drugs that are used to kill cancer cells. However, some chemotherapy drugs can cross the blood-brain barrier to treat some malignant brain tumors.

Types of Brain and Spinal Cord Tumors

Sometimes brain tumors are found not to have started in the brain but rather to have spread, or metastasized, from some other part of the body. Tumors that start in other organs and then spread to the brain are called metastatic brain tumors and those that start in the brain are called primary brain tumors. This is important because metastatic and primary brain tumors are usually treated differently.

In children, metastatic tumors to the brain are much less common than primary brain tumors. Unlike other cancerous tumors, tumors arising within the brain or spinal cord rarely metastasize to distant organs. They cause damage because they spread locally and destroy normal tissue where they arise. This document only covers primary brain tumors.

Gliomas: This is not a specific type of cancer. Glioma is a general category that includes glioblastoma multiforme, primitive neuroectodermal tumors, anaplastic astrocytoma, astrocytomas, oligodendrogliomas, ependymomas, brain stem gliomas and optic gliomas. Because this word is often used in discussing brain tumors, it is defined here in an attempt to reduce confusion with it.

Tumors can form in any type of tissue or cell within the brain or spinal cord. Some tumors contain a mixture of cell types. The most common brain and spinal cord tumors of children are astrocytomas. The second most common are primitive neuroectodermal tumors (23%), and the third most common are other kinds of gliomas such as brain stem gliomas (15%). Ependymomas are the fourth most common at 9%. All the others are fairly uncommon and account for only 3%.

Astrocytoma: Most tumors that arise within the brain itself start in brain cells called astrocytes, a kind of glial cell. These tumors are called astrocytomas. About half of all childhood brain tumors are astrocytomas. Many astrocytomas cannot be cured because they spread widely throughout, and intermingle with, the normal brain tissue. They are called infiltrating astrocytomas. Sometimes infiltrating astrocytomas spread along the cerebrospinal fluid pathways. But it is very rare for them to spread outside of the brain or spinal cord.

Infiltrating astrocytomas are classified as low grade, intermediate grade, or high grade. A pathologist (a doctor specializing in the diagnosis of diseases by laboratory tests) will grade them based on how the cells from a biopsy specimen (sample of the tumor) look under the microscope. Low-grade astrocytomas are the slowest growing and the most common type of astrocytoma in children. Intermediate-grade astrocytomas, or anaplastic astrocytomas, grow at a moderate rate. The highest-grade astrocytomas, glioblastomas, are the fastest growing.

There are some special types of astrocytomas that tend to have a particularly good prognosis. These are juvenile pilocytic astrocytomas and subependymal giant cell astrocytomas.

* Juvenile pilocytic astrocytomas most commonly occur in the cerebellum but also occur in the optic nerve, hypothalamus, brain, or other areas.

* Subependymal giant cell astrocytomas occur in the ventricles and are almost always associated with tuberous sclerosis (an inherited condition which may also cause epilepsy, mental retardation, and tumors of the skin and kidneys).

Certain tumors possibly of mixed glial and neuronal origin that occur in children and young adults and rarely in older adults also have a good prognosis. One such tumor is the pleomorphic xanthoastrocytoma and another is the dysembryoplastic neuroepithelial tumor. Although they appear malignant under the microscope, these tumors are relatively benign and most are cured by surgery alone.

Oligodendrogliomas: These tumors start in brain glial cells called oligodendrocytes. They spread or infiltrate in a manner similar to astrocytomas and, in most cases, cannot be completely removed by surgery. A small number of oligodendrogliomas, however, are associated with long-term survival of 30 or 40 years. Oligodendrogliomas may spread along the cerebrospinal fluid pathways but rarely spread outside the brain or spinal cord.

Optic Glioma: Optic gliomas are low-grade tumors of childhood and are frequently associated with an inherited condition called neurofibromatosis-type 1. These tumors, which arise from the optic nerve, can sometimes be treated successfully by surgery. At other times radiation therapy or chemotherapy may be required. The tumors are rarely lethal but may cause substantial visual loss.

Ganglioglioma: This tumor contains both mature neurons and glial cells. It has a high rate of cure by surgery alone or surgery combined with radiation therapy.

Primitive neuroectodermal tumors: Almost one fourth of brain tumors in children are of this type. They are rare in adults. When these arise in the cerebellum, they are called medulloblastomas. They are fast-growing tumors that can spread along the spinal cord and meninges but can be treated. Up to 50% of cases are cured by surgery and radiation therapy, sometimes with added chemotherapy. About 15% of childhood brain tumors are medulloblastomas.

Primitive neuroectodermal tumors are called pineoblastomas when they occur in the pineal gland. Other forms of primitive neuroectodermal tumors are all rapidly growing tumors that frequently spread throughout the cerebrospinal fluid pathways. The outlook for pineoblastomas is not as favorable as for medulloblastomas.

Ependymomas: Almost 10% of brain tumors in children are ependymomas. These tumors arise from the ependymal cells that line the ventricles or central canal of the spinal cord. Ependymomas may block the exit of cerebrospinal fluid from the ventricles causing the ventricle to become very large – a condition called hydrocephalus. Unlike astrocytomas and oligodendrogliomas, ependymomas usually do not spread or infiltrate into normal brain tissue. As a result, some but not all ependymomas can be removed and cured by surgery. Spinal cord ependymomas have the greatest chance of surgical cure. Ependymomas may spread along the cerebrospinal fluid pathways but do not spread outside the brain or spinal cord. Ependymomas represent about 9% of childhood brain tumors.

Choroid plexus tumors: These tumors arise in the choroid plexus within the ventricles of the brain. They are usually benign and cured by surgery (choroid plexus papillomas). However, they may also be malignant (choroid plexus carcinomas).

Craniopharyngioma: This type of tumor arises above the pituitary gland but below the brain itself. Most craniopharyngiomas are very close to the optic nerve, making surgical removal difficult, because of possible damage to the childÂ’s vision. They may also compress the pituitary gland and the hypothalamus causing hormonal problems. Some are cured by surgery; others require radiation therapy.

Schwannoma (neurilemoma): This type of tumor starts in Schwann cells that surround and insulate cranial nerves and other nerves. Schwannomas are usually benign tumors that often form near the cerebellum and in the cranial nerve, which is responsible for hearing and balance. They also arise from spinal nerves after they have left the spinal cord and can compress the spinal cord causing weakness, sensory loss, and bowel and bladder problems. These tumors are rare in children and when present in this age group, particularly if there is more than one, might suggest an inherited familial tumor syndrome such as neurofibromatosis.

Meningioma: This type of tumor arises from the meninges, the tissue that surrounds the outer part of the brain and spinal cord. Meningiomas cause symptoms by pressing on the brain or spinal cord. Meningiomas are much less common in children than in adults.

Meningiomas are benign and are usually cured by surgery. Some meningiomas, however, are located dangerously close to vital structures within the brain and cannot be cured by surgery. Meningiosarcomas are rare but very malignant (cancerous) tumors that may come back many times after surgery or, in rare occasions, spread to other parts of the body.

Chordoma: This tumor starts in the bone at the back of the skull or at the lower end of the spinal column. Chordomas may come back many times over a period of 10 to 20 years causing progressive neurologic damage and deterioration. But they usually do not spread or metastasize to other organs.

Germ cell tumors: Germ cell tumors develop from germ cells that normally form eggs in women and sperm in men. During normal embryonic and fetal development, germ cells migrate to the ovaries or testicles and develop into eggs or sperm cells. Sometimes, however, a few germ cells may not migrate properly and end up in abnormal locations such as the brain. They may then develop into germ cell tumors similar to those that can form in the ovaries or testicles.

Germ cell tumors of the nervous system usually occur in children, most often in the pineal gland or above the pituitary gland. The most common germ cell tumor of the nervous system is the germinoma, which can be cured by radiation therapy and possibly chemotherapy in almost all cases. Other tumors of germ cell origin such as choriocarcinoma or yolk sac tumors are rarely cured by surgery. Both radiation therapy and chemotherapy are used in their treatment and in some cases this may not control the tumor completely. Germ cell tumors can sometimes be diagnosed without a biopsy by measuring certain chemicals in the cerebrospinal fluid or blood.

Neuroblastoma: Another kind of nerve cell tumor, which is not a brain tumor, is called neuroblastoma. This is the third most common cancer in children. Neuroblastomas rarely develop in the brain or spinal cord; most develop from nerve cells inside the abdomen or chest. This type of cancer is most commonly diagnosed during early infancy. Neuroblastoma is discussed in a separate American Cancer Society document.