Metastatic brain tumours are cancers that grow in the brain through a primary cancer growing in another part of the body. The primary cancer may be lung, colon, breast, lymphoma, leukaemia etc. They frequently occur in the cerebrum (80%), the cerebellum (13-16%) and the brainstem (3%). Fifty percent of the time, multiple metastatic brain tumours are present. Most are diagnosed after their primary cancer has been diagnosed and treated. About one-third of people with metastatic brain tumours have not been previously diagnosed with cancer, and their central nervous system symptoms are the first indication of cancer. In about half of these people, the primary site will never be found.
Headache: Initially the headache comes and goes, and is usually common in the morning. It gradually increases in duration, frequency and severity
Weakness: One side of the body is weak
Behavioural changes: Some examples include impairment of judgement, reasoning, memory loss, rapid mood changes and mental confusion
Neurological: Drowsiness, changes in vision, speech disturbance, balance problems, clumsy unsteady walk, dizziness and vomiting
Seizures: May be the first indication
The diagnosis is based on the medical history, neurological examination and computed tomography (CT) or magnetic resonance imaging (MRI) scans. If there is no history of cancer, it is necessary to undergo more extensive testing to determine the primary cancer such as blood, urine and stool tests, chest x-ray, colonoscopy, chest/abdominal CT scan and mammography.
Treatment goals depend on the patient and other factors. The goal may be cure or relief of symptoms.
Biopsy: Removal of a small piece of tumour to confirm the exact nature of the tumour or to help diagnose the primary cancer if it has not yet been determined
Resection: This is recommended if the patient’s health is good, there are no other metastases in other parts of the body, the primary cancer does not respond positively to radiation therapy, and there is a single metastasis that can be approached surgically without causing undue neurological damage. Resection is usually followed by whole-brain radiation.
Radiation kills cancer cells directly or interferes with their growth. Two types of radiation therapy are available.
Conventional radiation therapy: The whole brain is radiated over one to two weeks. It may be the only treatment used by patients with lymphoma or small cell lung cancer because these cancers are very radiosensitive. Whole brain radiation often follows surgical resection. 60-80% of all patients respond to radiation therapy by experiencing relief of symptoms.
Radiosurgery: Radiosurgery is carried out using the Novalis Shaped-Beam machine located at the NNI-Khoo Teck Puat Radiosurgery Suite at Singapore General Hospital (SGH) Level B1, Block 2. This delivers narrow beams of strong radiation aimed precisely at the tumour from many different directions. Normal brain tissue therefore receives only a fraction of the total radiation dose received by the tumour. Exact knowledge of the tumour location is necessary, and this is achieved by securing the head firmly but painless in a custom-made mask system and doing a CT scan of the head with the mask system in place. For treatment planning, a MRI scan of the head is also required. Radiosurgery is as good as surgery combined with postoperative radiation for treatment of brain metastases. Hospitalisation is not required, and there is no risk of infection or surgical complications. However the result of radiosurgery is not immediately obvious.
Chemotherapy is recommended for spinal fluid metastases and is still under investigation for use against metastatic brain tumours. If the primary tumour is hormone dependent, hormones or hormone-blocking drugs may be used. Breast cancers that are oestrogen-receptor-positive are treated with tamoxifen which may also shrink the metastatic tumours. Prostate cancer metastases may also be treated by hormones. Steroids may be effective in patients with lymphoma.
Steroids such as Dexamethazone, act rapidly to decrease the symptoms of raised intracranial pressure due to brain swelling that accompanies metastatic brain tumours but do not kill the tumour cells. Improvement is noticeable within six to twenty four hours. This therapy is effective in sixty to eighty percent of patients with metastatic brain tumours. Steroids are frequently prescribed during the course of radiation therapy to reduce the swelling caused by radiation.
Steroid use is monitored by the doctor because of its potential side effects e.g., gastric pain and haemorrhage, aggravation of diabetes mellitus and reduced ability of the body to fight infection etc.
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