Central Nervous System Tumours - This Battle Which I Must Fight: Cancer in Canada's Children and Teenagers

CENTRAL NERVOUS SYSTEM TUMOURS

A tumour in the confined space of the skull or spinal column puts pressure on and damages surrounding tissues. Whether benign or malignant, it can be fatal. However, only central nervous system tumours confirmed malignant by biopsy or presumed malignant on the basis of clinical or X ray examination are described in this book.

Along with the lymphomas, malignant central nervous system tumours are the second most common cancer in the young (birth to age 19 years), accounting for 17 percent of all cancers in this age group. Over 200 children are diagnosed with a central nervous system tumour each year in Canada and the incidence is approximately 20 percent higher in boys compared to girls (Table 1).

Ninety percent of central nervous system tumours originate in the brain; the remainder in the spinal cord. The different tumour types, some of which are more aggressive than others, are identified by their location in the brain and by the appearance of their cells under the microscope.(100) Half of the brain tumours in this age group are astrocytomas; medulloblastomas and ependymomas account for a further 20 and 10 percent respectively.

Symptoms of a central nervous system tumour are related to the location of the tumour. The most common symptoms of a brain tumour include headache, vomiting, and sometimes seizures or ataxia (loss of balance). These are caused by increased pressure within the head and irritation of, or damage to, an adjacent portion of the brain. Spinal cord tumours can cause back pain, weakness, and poor bladder and bowel control.

Brain tumour cells spread primarily by invading adjacent brain tissue. They can be shed into the cerebrospinal fluid and grow anywhere within the central nervous system; however, a brain tumour rarely spreads to parts of the body outside the central nervous system.

Known risk factors account for a small proportion of these tumours and include exposure to ionizing radiation and certain rare genetic syndromes.

When a brain tumour is suspected, a test such as a CT (computed tomography) scan or MRI (magnetic resonance image) of the brain is used to locate the tumour. Whenever possible, some or all of the tumour is removed surgically. Sometimes radiation is given prior to surgery to shrink the tumour. Where a biopsy cannot be performed safely, treatment is given for the most likely tumour that would arise in that region of the brain.

The specific treatment depends upon the type of brain tumour, its location and the age of the child. If there is increased pressure within the skull, a shunt (tube) may be inserted surgically to drain fluid from around the brain. This lowers the pressure and eases the symptoms. Radiation therapy plays a major role in the treatment of most childhood brain tumours.(87) However, because it can result in significant permanent damage to the developing brain, radiation therapy is usually postponed until children are at least three years of age, when brain development is more complete.(20,39) The role of chemotherapy in the treatment of brain tumours continues to evolve. Multi-agent chemotherapy has significantly increased disease-free survival for some children with medulloblastoma or astrocytoma. A successful response to chemotherapy can delay the need to give radiation therapy to very young children.(14)

The prognosis for long-term survival depends upon the type and location of the tumour, how much of the tumour could be removed surgically, the presence or absence of tumour spread, and the age of the child or teenager at the time of diagnosis.(1,29) In Canada, the five-year survival rate for children and teenagers diagnosed with a tumour of the central nervous system between 1985 and 1988 was approximately 60 percent (Table 7).

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