Medulloblastomas

RELATED CONDITIONS: Supratentorial primitive neuroectodermal tumors, neurofibromatosis (von Recklinghausen disease), Gorlin syndrome

DEFINITION: Medulloblastomas are (cancerous) or benign (noncancerous) tumors that form in the cerebellum of the brain. The cerebellum controls balance and movement, posture, and speech. These tumors occur more often in children, but they may rarely appear in adults.

Risk factors: There is no known cause of medulloblastomas, but scientists are uncovering changes in genes and chromosomes that may influence the development of these tumors. A small percentage of tumors may tend to occur in families, particularly in families with neurofibromatosis (von Recklinghausen disease), an inherited disease that causes benign tumors to occur on peripheral nerves in the body. A few individuals with Gorlin syndrome, an inherited disease related to basal cell carcinoma and other conditions, also develop medulloblastoma. Turcot, and Li-Fraumeni syndromes are also being explored as risk factors, along with exposure to certain viruses. Boys are more likely to develop medulloblastomas.

Etiology and the disease process: Medulloblastoma is a relatively rare disease with few known causes other than a familial tendency. The tumor is considered fast-growing. Because of its location, walking and talking disruptions are expected as the disease progresses.

Incidence: The tumor occurs more often in boys than girls, and generally before the age of eight, with a peak incidence between five and ten years of age. In the United States, the incidence of medulloblastoma is 1.5 to two cases per 100,000 population (children). Approximately 350 to 500 cases are diagnosed annually, accounting for between 15 and 25 percent of brain tumors in children, according to the National Institutes of Health.

Symptoms: The classic initial symptoms of medulloblastoma are morning headaches, nausea, vomiting, and other flu-like symptoms. Because the symptoms mimic flu, the tumor may go undiagnosed until symptoms progress to balance problems. Older children may be more easily diagnosed than infants, as infants may initially exhibit an increase in head size and irritability, both common in infants as they grow and develop. Vomiting may make the person feel better as the intracranial pressure is temporarily relieved. Symptoms increase as the tumor grows.

Screening and diagnosis: There is no screening test for medulloblastoma. Diagnosis begins with a history of symptoms and neurological examination. Radiology studies include magnetic resonance imaging (MRI), including the use of a contrast dye to identify the presence of a brain tumor, and a positron emission tomography (PET) scan, used to determine if the tumor is active and growing. Other procedures, such as a lumbar puncture to take cerebrospinal fluid (CSF), a bone marrow aspiration and biopsy, and a bone scan, may be done to look for signs of cancer. A confirmed diagnosis is made during surgery, and a pathologic examination of the tumor specimen removed determines if the tumor is benign or malignant.

Two risk groups are used in childhood medulloblastoma to determine treatment management rather than the adult staging process. The average risk group and the poor risk group are differentiated based on the tumor remaining after surgery, the spread of cancer cells within the brain and spinal cord, or the distant spread of tumor cells to other parts of the body. Adults are staged based on the remaining tumor and whether the tumor has spread using the TNM (tumor/lymph node/metastasis) staging system.

Treatment and therapy: Treatment of medulloblastoma is with surgery, radiation therapy, chemotherapy, and, if necessary, mechanical diversion of cerebrospinal fluid with a to carry blocked fluid out of the brain. Surgery is used to remove as much of the tumor as possible. Imaging studies may show that the tumor is inoperable. A will still be done to determine the type of tumor and whether it is malignant. If the tumor has grown into the brain stem, removal may not be an option, as the side effects of removal are life-threatening. Steroids are used to decrease swelling in the brain. A shunt, or tube to drain CSF away from the brain, usually to the abdomen, may be placed during surgery. Radiation therapy to the brain and the spinal cord is then used to kill any cells remaining. Radiation may be done with stereotactic radiosurgery, intensity-modulated radiation therapy, or external beam radiation. C may be used in infants to postpone the use of radiation, as cranial radiation side effects may be severe. Chemotherapy may be given either intravenously (into a vein) or intrathecally (into the cerebrospinal fluid) by use of an Ommaya reservoir. In adults, chemotherapy effectiveness is less clear.

As the twenty-first century progresses, new treatments for medulloblastomas are becoming available. Doctors increasingly use a multimodality approach, combining all available treatments to increase effectiveness. The discovery of subtypes of medulloblastomas has led to more personalized treatment options. Proton therapy, targeted therapies, and intraoperative MRI have allowed for less invasive treatment options. Further, new medications are helping to relieve the side effects of treatment.

Prognosis, prevention, and outcomes: The prognosis for medulloblastoma varies with the patient’s age at diagnosis, the size of the tumor, the amount remaining after surgery, and the level of tumor cell spread to other sites in the brain, spinal cord, or elsewhere in the body (metastasis). Approximately 50 to 60 percent of adults are alive at five years after diagnosis, and up to 80 percent of children with average-risk classification can be expected to reach five years, according to the National Cancer Institute. The outcome for infants is poor, with a 30 to 70 percent survival, but clinical trials for infants, specifically, are increasing. There is no prevention for medulloblastoma. may be negatively affected by the side effects of therapy, including learning disabilities, hearing loss from drug therapy, obesity, thyroid deficiency, and other problems depending on treatment and site. Recurrence is always a risk, as tumors may be difficult to remove completely.

Bibliography

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