What is a Brain Metastasis?
A brain metastasis is a tumor that travels to the brain from another area of the body. If cancer is metastatic, it means that cancer cells from a tumor have spread to another area of the body through the blood stream, lymphatic drainage system, or by direct extension. The original source of the cancer, or primary cancer, determines the type of cancer, but the location where the new tumor develops is called the metastatic site or location. Brain metastases commonly migrate to the brain through the bloodstream, and tend to be found in areas where the size of the arteries narrow and cause the flow of blood to be slowed. Brain metastasis is usually indicative of an advanced state of cancer.
Lung cancer and breast cancer are the most common types of primary cancer that lead to brain metastases. Gastrointestinal (stomach and intestine) cancer and genitourinary (genital and urinary) cancer, as well as skin cancer are also commonly found to be the source of brain metastases. Once metastases are established in the brain they cause brain swelling and loss of neurological function. In many cases there is more than one metastatic tumor that arises, which can make treatment that much more difficult.
Incidence and Prevalence
Brain metastasis is the most common of all brain tumors, and the number of brain metastases diagnosed each year outnumbers all other brain tumors put together. The age bracket with the highest risk of brain metastasis is between 45 and 64 years of age, with a peak between the ages of 50 and 54 years (p.924 Brain Tumors). It is possible that multiple metastases will develop, but this is usually dependent on the type of primary cancer. As many as one in four cancer patients will develop brain metastases (www.neurosurgery.org).
Site of Predilection: The majority of metastases are found at the interface of the white and gray matter of the cerebrum. The cerebrum is the main portion of the brain in the upper area of the cranium. The rest of the tumors are typically found in the cerebellum region, and only occasionally in the brainstem or spinal cord.
Symptoms
Headache
- Focal weakness (motor weakness of a specific area such as one side of the face, an arm, a leg, or both an arm-leg.
- Mental and behavioral disturbances (impaired thinking, emotional changes)
- Seizure – an attack of epilepsy (which is a disturbance of the electrical activity of the brain causing convulsions and possibly loss of consciousness)
- Ataxia – the failure of muscle coordination and irregularity of muscular action.
- Aphasia – a defect in or loss of the power of expression by speech, writing. Or loss of comprehension of the spoken or written language due to injury or disease of the brain centers.
- Visual field defect (loss of vision)
- Sensory change (numbness or tingling.
Clinical Presentation
The majority of brain metastases present with at a mild headache that may slowly increase in severity. The headaches often occur at night and are the result of increased pressure on the brain caused by tumor growth. As the tumor grows pressure on the brain increases resulting in the loss of brain functions such as noted above in the symptoms section. If untreated, the loss of function may be permanent or progress to more serious problems such as paralysis and/or coma.
Seizures are not as common, but do occur
Diagnosis
Contrast enhanced magnetic resonance imaging (MRI) is the best test for diagnosing brain metastasis. Magnetic resonance imaging is basically a photograph of the brain’s tissues, used to highlight those tissues that do not have a uniform makeup. By adding a contrast agent, the lesion(s) are more likely to show up on the image. MRI’s are also used to determine the total number of metastases, and their location. If the patient has a known primary cancer, the combination of clinical symptoms and the appearance of a secondary brain lesion on the MRI is usually enough evidence for a diagnosis. However, physicians must be conscious that there are many other possible reasons for a secondary lesion to present itself on an MRI (such as a stroke or brain abscess). A biopsy, which is a procedure to obtain a tissue sample from the lesion, is often taken to determine the etiology of the lesion (abscess, stroke, or tumor).
Treatment
There are a number of treatment options available to treat brain metastases; however the options available to each individual patient are limited. Once a brain metastasis has been diagnosed, corticosteroid treatment should begin immediately to control brain swelling (fluid in the brain surrounding the tumor) and intracranial increases in pressure. Treatment must be individualized to each patient, and because most patients with brain metastasis have already undergone treatment for primary cancer the physician has even more factors to consider. A management plan should be developed that takes into consideration the best combination of treatment options for each patient.
General Management Plan: Once diagnosed, the highest level of success for treating brain metastasis is typically found using: corticosteroids (used to control brain swelling), radiotherapy (localized doses of radiation to the area of metastasis over time), surgery (removal of as much of the tumor as possible), stereotactic radiosurgery (an intense dose of radiation targeted at the area of metastasis). Also used if thought to be beneficial: chemotherapy (cytotoxic drugs that combat tumor growth) and brachytherapy (a small amount of radioactive material implanted into the area of metastasis).
Radiotherapy is generally thought to be the most effective treatment for brain metastases, but corticosteroid treatment should continue during radiotherapy. Whole brain radiation therapy (WBRT) is the most widely and commonly used treatment for patients with brain metastasis. WBRT has been shown to alleviate the effects of the cancer, as well as extend the life of the patient. WBRT is also the most effective way to target the growth of very small tumors that are not picked up by MRI or CT. WBRT is also used post-operatively as a deterrent for the re-growth of tumor cells.
Side effects from radiotherapy are determined by a variety of conditions, for example, how long the treatment has been undergone, how high the doses of radiation are, and individual susceptibility. Side effects of radiation therapy include: hair loss, dry skin that can lead to peeling in large sheets, headaches, nausea, lethargy, otitis media (inflammation of the inner ear), and brain edema leading to increased ICP. There are also cases of extreme dementia in survivors of WBRT.
Lower doses of radiation should be given to patients who have previously undergone radiotherapy, and aggressive radiation therapy should only be considered as a way to extend survival in the short-term. Even if a patient responds well to radiotherapy, there are limits to how much is safe. The longer the patient is exposed to radiation the more severe the side effects of radiation become. Therefore, if the projected survival is longer that one year, other treatment combinations should be sought out. (Most patients undergoing WBRT alone do not typically survive more than a year.)
Surgical Management: As much of the tumor should be extricated during surgery, without damaging the healthy tissue. The largest factor in the decision to operate and remove a portion, or all of a tumor, is its accessibility and proximity to sensitive areas of the brain which may be compromised during the operation. However, if there are extenuating circumstances like advanced edema, increased ICP, or other threatening medical conditions which could be alleviated by surgical removal of the tumor, then these considerations should take precedence in the decision to operate.
Approximately two-thirds of patients with brain metastases have multiple lesions, which makes the removal of tumors difficult and often ineffectual. Surgery is typically not a recommended option if multiple brain metastases are present. In the case of one or two metastases it should be considered only if the tumors are accessible, and once the tumors are removed radiotherapy should be used to prevent tumor re-growth for as long as possible.
Chemotherapy: The success of chemotherapy in the treatment of brain metastasis is not encouraging, but is a treatment option, especially if the patient has responded to chemotherapy in the past. Chemotherapy is problematic in treating brain metastasis because the blood-brain barrier prevents chemotherapy drugs from entering the brain, and reaching their target. Chemotherapy is often used in conjunction with other treatment.
Interstitial brachytherapy is a technique that uses radioactive implants in the tumor, and can be done surgically or stereotactically (non-invasive), but can cause radiation necrosis (death of living cells).
Prognosis
The prognosis for a brain metastasis is typically less than one year, and mortality more commonly ranges from a few days after diagnosis to a couple months without treatment. Patient survival is often increased with surgical removal of the tumor prior to treatment with radiotherapy. With a favorable prognosis, patients diagnosed with brain metastasis typically live for 18-24 months after treatment. With successful treatment, patients will sometimes live longer, however brain metastases are prone to re-growth and their very nature makes them difficult to contain. Early diagnosis is essential for successful treatment and survival.
