What are medulloblastomas?

Related conditions:
Supratentorial primitive neuroectodermal tumors, neurofibromatosis (von Recklinghausen disease), Gorlin syndrome

Definition:



Medulloblastomas are malignant (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 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.

Etiology and the disease process: Medulloblastoma is a relatively rare disease, with no known cause other than a familial tendency. The tumor is considered fast growing. Because of the location of the tumor, walking and talking disruptions are common 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 2 cases per 100,000 population (children). Approximately 1,000 cases are diagnosed annually, accounting for 18 percent of brain tumors in children, according to the American Brain Tumor Association.

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 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, spread of cancer cells within the brain and spinal cord, or 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 shunt 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 biopsy 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. chemotherapy 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.

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 57 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 American Brain Tumor Association. With poor risk classification, up to 65 percent of children may survive to five years. The outcome for infants is poor, with a 30 to 50 percent survival. There is no prevention for medulloblastoma. Quality of life 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.

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