Medulloblastoma is a solid, cancerous tumor originating in the cerebellum of the brain. It is also known as a primitive neuroendocrine tumor.
Description
Medulloblastoma is the most common cancerous brain tumor of childhood. It accounts for 20% to 25% of all childhood tumors. Medulloblastomas can occur soon after birth and into puberty, but most tumors occur either before age ten or sometime in the late teens or early twenties. If these tumors are left untreated, they can spread to other areas of the brain and to the spine.
Medulloblastomas occur in the area of the brain known as the cerebellum. The cerebellum, located in the back of the brain above the neck, is the area of the brain responsible for controlling and integrating movement. A person could move their muscles without the aid of the cerebellum, but their movements would be clumsy and disorganized. Medulloblastoma tumors in the cerebellum can cause loss of functioning of the cerebellum, leading to this uncoordinated movement, called cerebellar ataxia.
If medulloblastomas are not detected early, they may spread cancer throughout the brain or spinal cord. If the cancer spreads to the spinal cord, a child may begin experiencing severe back pain, difficulty walking, and the inability to control their bladder and bowel functions.
Demographics
As stated earlier, medulloblastoma is a childhood cancer, occurring mainly in the first ten years of life. About half of all medulloblastomas occur in children aged five or younger. Boys tend to develop the tumors more than girls at a rate of approximately two to one. There are no current studies comparing the incidence of medulloblastoma between different racial and ethnic groups.
Causes and symptoms
Besides being male, there are no other known risk factors for medulloblastoma. This type of tumor can occur in association with two rare types of genetically linked family cancer syndromes, Gorlin's syndrome and Turcot's syndrome. Gorlin's syndrome is caused by a defect in a gene known as PTC located on chromosome 9. This defect can cause medulloblastoma as well as cancers of the skin and ovary. Turcot's syndrome is caused by a defective gene known as APC, and can present with cancer of the intestinal tract as well as medulloblastoma. It should again be stated that both of these syndromes are quite rare and only account for a fraction of medulloblastoma cases seen and reported.
Medulloblastoma can present in many ways. In infants, symptoms of the tumor can include an unusual increase in head size, vomiting, irritability, and lethargy. Since all infants generally have these symptoms at one time or another, it can be difficult for a parent or even a health care worker to recognize the initial presentation of medulloblastoma in babies and toddlers.
In older children and teenagers, medulloblastoma can present the same as in infants or much differently. Non-specific symptoms such as nausea and vomiting, headache, and vague visual disturbances can be the first sign of a tumor in the cerebellum. Other, more striking signs can be double vision, sudden difficulty writing, and problems walking and moving that worsen over time.
Diagnosis
The diagnosis of medulloblastoma is made with both clinical observation and imaging studies. If a parent has noticed some of the signs and symptoms listed above, then a visit to a pediatrician is certainly warranted. During the office visit, various specialized neurological tests will be done to see if there is any sign of a problem in the cerebellum or surrounding brain structures.
If there are indications of a tumor, then imaging studies can be done to see if a tumor can be detected. The two types of imaging studies done to detect medulloblastoma are magnetic resonance imaging (MRI) and computed tomography (CT) scan. The MRI uses a high-strength magnetic field to visualize the brain, and is very useful for detecting medulloblastomas. The CT scan uses x ray images reconstructed by computer. Like the MRI, a
CT scan is also useful for detecting brain tumors as well as tumors that may have spread to the spine.
Treatment team
The treatment of medulloblastoma is optimally carried out in a medical center that has experience in treating this often difficult-to-treat cancer. Treatment and treatment planning is usually carried out by a multidisciplinary team of cancer specialists, including a pediatric oncologist (a doctor specializing in the treatment of childhood cancers), a pediatric neurosurgeon (a doctor specializing in childhood brain surgery), as well as a pediatric neurologist and radiation oncologist (a doctor specializing in the use of radiation to treat cancer).
Clinical staging, treatment, and prognosis
The staging of childhood brain tumors has become important to the selection of treatment plans, as well as giving information to make a more accurate prognosis. For medulloblastoma, there are four stages defined, as follows:
T1: the tumor is less than 3 cm in diameter.
T2: the tumor is greater than 3 cm in diameter and has invaded one other brain structure in addition to the cerebellum.
T3: the tumor has invaded two other brain structures besides the cerebellum.
T4: the tumor has spread down into the midbrain or upper spinal cord.
The treatment options for medulloblastoma have changed significantly over the past few decades. The first treatment option for medulloblastoma was surgery, and this is still the most common treatment. Surgeons try to remove the entire tumor, although this is sometimes not possible. After the surgery is completed, further treatment will depend upon whether or not the child has been placed in an "average risk" or "high risk" group. An average-risk child is defined as three years or older, with the tumor initially confined to the cerebellum with little to no tumor left after surgery. A high-risk child is defined as a child under three years of age, with the tumor initially spread into other areas of the brain besides the cerebellum, and with some of the tumor remaining in the brain after surgery.
Children in the average-risk group will often have radiation therapy applied to the area in their brain where the medulloblastoma tumor was, especially if the surgeon was not able to remove all of the tumor. Using radiation on children younger than three years may result in the child having growth retardation along with learning disabilities.
Because of the possible side effect of radiation, especially in children younger than three years of age, the use of certain medications called chemotherapy is being used more frequently for medulloblastoma. Researchers have found that medulloblastoma tumors are highly sensitive to chemotherapy, giving hope that chemotherapy can be used instead of radiation, especially for children at average risk. For children at high risk, the current recommendation is to use both radiation and chemotherapy, since this combination has been shown to improve overall survival rates for high-risk children.
In 1930, the anticipated survival rate for a child with medulloblastoma after surgery was less than 2%. Today, with the use of better surgical techniques, radiation, and chemotherapy, the prognosis for children in the average risk group has increased to a 60% survival rate over a five-year period. Children in the high-risk group do not fare as well, having a 30% to 35% survival rate over a five-year period.
Alternative and complementary therapies
Alternative and complementary therapies are those that fall outside the scope of traditional, first-line therapies such as surgery, chemotherapy and radiation. Complementary therapies are meant to supplement those traditional therapies with the objective of relieving symptoms. Alternative therapies are nontraditional, unproven attempts to cure the disease.
Numerous alternative therapies exist in cancer treatment. Plant extracts, vitamins, protein therapies, and natural substances such as mistletoe and shark cartilage have all been touted as cancer-fighting remedies. However, some alternative therapies, such as Laetrile, can produce dangerous side effects and have shown no anti-cancer activity in clinical trials. Patients interested in alternative therapies should consult their doctor to ensure that the products are safe, especially for children, and do not interfere with regular cancer treatment.
Coping with cancer treatment
During treatment, a child's health will be followed by the team of physicians involved. Those physicians will be able to monitor the child for any side effects from the treatments, especially if the child is receiving chemotherapy. The most frequent side effects of chemotherapy can include nausea and vomiting, diarrhea, fatigue, and hair loss(alopecia). With medications,
physicians can often treat some of the side effects, especially nausea, vomiting, and diarrhea.
Cancer treatment can be especially frightening for a young child. Family support is critical, and parents should consult their physician about any organizations in the area that can help their child cope with the effects of medulloblastoma and its treatment.
Clinical trials
There are many clinical trials being done to help better the treatment options for medulloblastoma. Some of the most promising ones are studies in which peripheral stem cell transplantation is used. This is a technique in which certain cells in the body known as stem cells are used to replace other, depleted cells, such as the immune cells and blood cells that are destroyed when chemotherapy is used. It is hoped that with stem cell use, physicians will be able to use higher doses of chemotherapy in order to destroy the medulloblastoma cancer.
Prevention
There are currently no known ways to prevent medulloblastoma. Those who have the very rare genetic disorders which predisposes them to medulloblastoma, Gorlin's and Turcot's syndrome, should be especially aware of any signs or symptoms of medulloblastomas. Children of parents with these genetic disorders should have routine screening done by a pediatrician for any signs of a brain tumor.
Abeloff, Martin, James O. Armitage, Allen S. Lichter, and John E. Niederhuber. Clinical Oncology. New York: ChurchillLivingstone, 2000.
ORGANIZATIONS
American Brain Tumor Association. Suite 146, 2720 River Rd., Des Plaines, IL 60018. (800) 886-2282. <http://www.abta.org>.
National Cancer Institute, National Institutes of Health. Building31, Room 10A31, 31 Center Dr., MSC 2580, Bethesda, MD20892-2580. (800) 4-CANCER. <http://www.nci.nih.gov>.
St. Jude Children's Research Hospital. 332 N. Lauderdale St., Memphis, TN 38105. (901) 495-3300. <http://www.stjude.org>.
