sections include: dealing with childhood brain tumors, the treatment triad, gliomas, embroynal tumors, other types of childhood tumors
The word tumor simply means a growth. If a tumor grows rapidly beyond the body’s normal control system, disrupts healthy tissue, or spreads (metastasizes) to other parts of the body, it becomes a cancer.
All cancers seem to arise from a defect in the critical cells’ genes; put simply, either a growth-causing gene goes too far, or a growth-halting gene stops working. Some cancerous tumors grow more slowly or compactly than others, and treatment for each case is determined by the quality and location of the tumor. There are several significant differences between tumors that appear in childhood and those that appear in adulthood. To begin with, cancer is more common in adults than in children. This may be because failure of control mechanisms is more likely as the body ages. While people can inherit an increased risk for certain cancers, the mutated genes in childhood cancers seem in almost all cases to be confined to the abnormal cells. Thus, children are unlikely to pass on the disorder if they grow up and have children of their own.
About 1 in every 350 U.S. children will be diagnosed with cancer before the age of 20. Fortunately, over 70 percent of these children live for at least five years after treatment; that is a better survival rate than for adults, and it continues to improve. The most common form of cancer in children is leukemia, which arises from white blood cells and accounts for about 30 percent of all cases. The second most common form (19 percent) is tumors of the brain. (In contrast, brain tumors make up less than 2 percent of cancers in adults.)
Dealing with Childhood Brain Tumors
Tumors growing inside the skull produce a wide range of symptoms, depending on their characteristics and the age of the child. Very young children may not be able to express their difficulties in words, of course. Slow-growing tumors may cause symptoms to appear gradually, so children and their parents do not initially connect headaches, school difficulties, or clumsiness with a growth in the brain. Pediatricians may also suspect that particular symptoms are caused by sinus infections, intestinal problems, viruses, or other illnesses much more common in childhood than cancer. On the other hand, some brain tumors announce themselves through seizures or other dramatic symptoms that send a family to a hospital immediately. (Tumors account for less than 1 percent of all childhood seizures, however.)
One of the more common ways tumors can harm the brain is by blocking the drainage of cerebrospinal fluid from the head, producing hydrocephalus, whose symptoms can show up in a variety of ways. In an infant whose skull bones have not fused, the head can become visibly swollen. In older children, the most common effect of hydrocephalus is headaches; a regular headache on getting out of bed that is relieved by vomiting is an especially important sign. Other signs include unusual irritability, loss of appetite, and loss of motor or intellectual abilities.
Tumors can also invade or push against structures of the brain, disrupting particular functions. For instance, a cancerous growth in or around the brain stem can cause problems with balance and coordination, abnormal speech, and weakness in a portion of the face. A tumor in the cortical areas can produce headaches, seizures, weakness in one limb or side of the body, and subtle changes in personality and thinking. Tumors affecting the visual pathways can cause loss of sight, quickly or gradually, completely or partially.
A pediatrician’s initial response will focus on any acute symptoms, especially making sure hydrocephalus does not permanently damage the child’s brain. If doctors suspect the underlying problem might be a brain tumor, they recommend a variety of further tests. Computed tomography (CT) and magnetic resonance imaging (MRI) scans detect nearly all brain tumors and also help determine whether a cancer has metastasized to other parts of the nervous system. A lumbar puncture (spinal tap) may also be necessary to check for abnormal cells in the cerebrospinal fluid. A neurological exam may be useful, depending on how well the child can cooperate. To determine the exact nature of the tumor, however, it is usually necessary to obtain a sample of its cells and study them in the lab—the process called biopsy. For growths inside the skull, biopsy requires surgery because there is no other way to reach the tissue.
If a child has been diagnosed with a cancerous brain tumor, there is still hope. As stated above, well over half of children diagnosed with cancer today live for at least five years. Still, fighting and recovering from cancer is a difficult challenge for children and their families. Some diagnostic or treatment procedures are painful or exhausting. Some side effects can also be difficult in both short term and long term: chemotherapy and radiation may cause adolescents to lose their hair when looking good seems most important. And of course, any threat to the life of a young person is sad and frightening for everyone involved. Often the prospect of death is more emotionally devastating for parents and other adults than it is for children. Parents may also have the responsibility of looking after siblings of the child with cancer, helping them through their worries and making sure they don’t feel neglected.
On top of the emotional impact, families must deal with a complex system of names and treatments for different types of tumors. The remainder of this section will briefly discuss the three main forms of cancer treatment and then various tumor types and the best treatment for each. However, every child’s prognosis and treatment depends on his or her particular condition, so families should work closely with their doctors when making any treatment decision.
The Treatment Triad
The goal of all cancer treatments is simple: to remove or disable the harmful cells while leaving normal cells as healthy as possible. Children with cancers are generally more resilient than adults in the same situation, who often have other health problems. This means that doctors can treat childhood cancer a little more aggressively (with the exception of radiation, discussed below) than adult cancers.
Most children diagnosed with brain tumors or other types of cancer receive care through specialized cancer centers. These facilities provide the widest range of treatments and expertise; dealing with brain tumors often requires a team that includes cancer specialists (oncologists), pathologists, neurosurgeons, nurses, nutritional counselors, and others. Cancer centers also provide valuable support services for children and their families: psychological counseling, discussion groups, even the chance to make friends with other children dealing with the same experiences.
Surgery is the treatment of choice for most brain tumors in children. Neurosurgeons try to remove all the cancerous tissue, or as much as possible, without hurting the surrounding structures— a tricky challenge when dealing with an organ as vital as the brain. MRI helps in this task by letting surgeons see the growth area more clearly. Very young brains show more plasticity than older ones, so children are more likely than adults to recover from the loss of brain tissue and achieve normal functioning again. Often a surgeon must also deal with the hydrocephalus a tumor has caused, inserting a tube (shunt) in the head to drain excess cerebrospinal fluid.
Chemotherapy involves using medications to kill the cancerous cells in a person’s body. Again, the challenge is not to allow the same drugs to do too much damage to a person’s healthy growing cells. Brain tumors are more difficult to affect by chemotherapy than tumors in other parts of the body because of the blood-brain barrier, which keeps poisons in the blood out of the brain. The choice of medications and their schedule (before, during, or after other treatments) depend on the nature of the tumor.
Chemotherapy in high doses can kill a child’s bone marrow along with the cancerous cells; both types of tissue produce new cells quickly, but the red blood cells created by bone marrow are crucial to healthy life. In treating leukemia, doctors often prepare for that problem by removing and saving some of the child’s own marrow tissue or stem cells—replacing them in the child’s body after the chemotherapy is over. This is called autologous bone marrow rescue and allows for more aggressive chemotherapy. The same technique offers promise for treating brain tumors.
Radiation is another way to attack cancerous cells without physically invading a child’s body. This type of therapy poses more dangers for children, especially infants, than it does for adults because the same energy that can stop harmful cells from spreading can also affect other cells’ normal growth and development. As a result, young children who have had radiation therapy show a higher risk for delayed intellectual development and pituitary deficiency. With stereotactic radiosurgery, the radiation beam can now be shaped to focus on particular parts of the brain without penetrating other regions. In general, however, oncologists still use radiation less often for children than for adults, and even less often for children under 2.
In addition to helping doctors detect and operate on brain tumors, advanced MRI techniques are also useful in tracking the effect of treatments. Imaging can show tissue growth or shrinkage with great accuracy and help detect any spread or recurrence of the disease. Children who have had a brain tumor often return for periodic MRI scans months after treatment to confirm that no sign of cancer remains.
Gliomas are tumors that grow from the glial cells that support the brain’s neurons. They are the most common form of brain tumor in children, accounting for half of all cases, and can start anywhere in the brain. Low-grade gliomas generally grow slowly and rarely spread. In contrast, high-grade gliomas (about 20 percent of all gliomas) grow aggressively, sometimes over only a few weeks, and often metastasize to other parts of the brain.
The lowest grade of glioma, found only in children, consists of pilocytic astrocytomas. Pathologists recognize these growths because their cells appear almost normal. They can occur in the optic nerves, hypothalamus, brain stem, and possibly the cerebral or cerebellar cortex. If such a tumor is accessible to a surgeon, completely removing it should allow the child to live a long and normal life. If not, the best way to manage such a lowgrade growth is biopsy and observation, to catch it quickly if it becomes more dangerous.
The slightly higher-grade fibrillary astrocytomas also grow slowly but pose more of a threat to a child. When such an astrocytoma appears in an easily accessed area—for example, the cerebral hemispheres—the best treatment is surgical removal. But when doctors find a low-grade astrocytoma where it would be dangerous to operate, they often consider radiation first. Astrocytomas are termed anaplastic and moved up one grade if they are invading brain cells. Surgery is often useful, but not enough on its own; radiation attacks the cancer that has spread.
The highest grade of glioma is termed glioblastoma multiforme, and it can be devastating in both children and adults. It is characterized by cell death (necrosis), a proliferation of blood vessels feeding the tumor, and markedly abnormal cells. The usual treatment is to remove as much of the growth as possible through surgery and then to use radiation on the tumor and for a short distance (three quarters of an inch) around. Chemotherapy is sometimes added but does not have a striking success rate. Survival is usually one to three years.
Another important variable among gliomas is where they appear. Tumors may thus be classified as optic nerve, hypothalamic, brain stem, hemispheric, and so on. The location often affects treatment. Gliomas of any grade in the brain stem are particularly difficult to remove surgically because of the high density of vital nerves there. Gliomas on the pons are usually high grade and have a bad prognosis, but about 30 percent of brain stem tumors are low grade, with much better long-term survival rates. There is a similar discrepancy between the two types of gliomas on the cerebullum, depending on how they have spread and affected the surrounding region:
- Type A tumors have a ten-year survival of 94 percent.
- Type B are more deadly, with a 29 percent ten year survival in one study.
Low-grade tumors in the area of the neck and medulla (cervicomedullary tumors) should be removed; even aggressive removal of brain tissue in this area has surprisingly few adverse effects. Gliomas on the optic nerves may be biopsied to determine the type of cells involved but probably do not need further treatment unless the child’s vision deteriorates, in which case radiation is the best treatment.
Other categories of gliomas are defined by the type of cells that make up the tumors. Cell characteristics help determine a child’s prognosis and treatment, so a biopsy is crucial in identifying these tumors:
- Xanthoastrocytomas are glial tumors with giant cells, often filled with fat. They have a better prognosis than most astrocytomas.
- Gangliogliomas involve cancerous growth by both neurons and glial cells, usually in the temporal or frontal lobes. They are rare in adults, less so in children. Often they cause seizures. Removing as much of the tumor as possible in surgery is the procedure of choice. Long-term survival is not unusual.
- Oligodendrogliomas arise from the cells called oligodendrocytes, which wrap myelin around neurons. Pathologists recognize these cells because they are small and regular, with an open “fried egg” structure beyond the nucleus. Surgical removal is the best course. Radiation therapy appears to add little. A genetic test helps predict how effective chemotherapy will be.
- Ependymomas (less than 10 percent of all childhood brain tumors) arise from the ependymal cells in the brain’s innermost lining, usually in the posterior fossa in children. They often produce hydrocephalus. The best treatment uses microsurgical techniques to remove the tissue and perhaps place a tube to drain cerebrospinal fluid. Radiation is important in treating ependymomas, but chemotherapy has limited effect.
Finally, some children develop tumors of mixed sorts, with components of oligodendroglioma or ependymoma along with astrocytoma.
About a third of all childhood brain tumors are termed embryonal, defined as containing small, round, uniform cells that appear blue when examined by microscope after staining. It is quite possible that these tumors arise from nervous system stem cells in which something has gone wrong. They generally grow quickly over weeks or months, spreading through the cerebrospinal fluid to other parts of the brain and spinal cord. In about 40 percent of children diagnosed with embryonal tumors, the cancer has already metastasized.
The most serious form of embryonal tumors are medulloblastomas, which arise in the cerebellum. These are quite harmful, both because of their aggressive growth and because they commonly cause hydrocephalus. In recent years it has become clear that the amount of medulloblastoma tissue a surgeon removes is important to a child’s outcome. Doctors once used radiation of the head and spine as a routine initial treatment for medulloblastomas; now MRI can provide clues as to whether a tumor has actually spread along the spine. As an alternative for children aged 2 and under, several cancer centers have tried chemotherapy using procarbazine, CCNU, and vincristine; in one study the two-year survival rate after this treatment was 96 percent.
Most other embryonal cancers are called primitive neuroectodermal tumors (PNETs). These can occur in the cerebral hemispheres and are treated by surgical removal as vigorously as possible, followed by radiation.
Other Types of Childhood Tumors
Retinoblastomas are malignant tumors of the retina, the inner layer of the eye. Usually these growths begin before a child is born and are recognized sometime during the first year, often because of a telltale white spot in the eye. Only about 200 cases are diagnosed in the United States each year, but the children involved usually lose sight in the affected eye(s). As long as the cancerous cells have not spread to the optic nerve, however, these children are almost certain to survive.
Choroid plexus papillomas are rare tumors arising from the small blood vessels and membranes that project into the brain’s ventricles. They may be malignant or benign. Surgical removal is the major method of treating these growths, but the operations are complex because the tumors are so closely connected with the brain’s blood supply.
Craniopharyngiomas develop at the base of the brain, around the pituitary gland. They are benign tumors, usually treated by surgical removal and radiation. These steps must be taken with care, however, because the treatment has an unusually high rate of such harmful side effects as visual loss, low pituitary function, and behavioral difficulties.
Tumors near the pineal gland can be roughly divided into two sorts:
- Germ cell tumors are often very sensitive to radiation; indeed, some doctors recommend trying radiation treatment first to see if they respond. They may be detected by increased alpha-fetoprotein (AFP) in a child’s cerebrospinal fluid, obtained through a spinal tap.
- Pineal parenchymal tumors require a biopsy and, if that test suggests there has been any change in tissue structure, probably excision.
Finally, children with neurofibromatosis of either type are at higher risk for brain tumors. These disorders cause other nervous system tumors as well, usually of less consequence. Optic nerve tumors appear in about 15 percent of people with neurofibromatosis 1, but this type of growth rarely spreads or produces harmful symptoms. Similarly, neurofibromatosis 2 is often associated with acoustic neuroma, a benign tumor most often found on the auditory nerve.
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