By Bahaa E. Hafez, MD
Brain metastases are tumors that originate in tissues or organs outside the brain and spread secondarily to the brain. These tumors are a common complication of systemic cancer and an important cause of morbidity (rate of disease) and mortality (death) in cancer patients. They are the most common intracranial tumors (tumors inside the skull) and their incidence may be rising. Approximately 170,000 new cases of brain metastasis are diagnosed in the United States each year.
Although virtually any malignancy can metastasize, or spread, to the brain, the incidence of brain metastasis varies dramatically from one type of cancer to another. Lung, breast, melanoma, renal and colon cancers account for the greatest majority of all brain metastasis. Primary lung tumors rank first, accounting for 30 percent to 60 percent of all brain metastasis. Twenty percent to thirty percent of patients with breast cancer will develop brain metastasis.
The incidence of brain metastasis is based on age. It peaks in the fifth to seventh decades and tends to decline after that. There is a lower incidence of brain metastasis in children than in adults, with frequencies ranging from 6 percent to 13 percent in children.
Although brain metastasis occurs at a similar frequency among men and women some differences are seen in the types of primaries responsible for the brain metastasis in the two genders. Lung cancer is the most common source of brain metastasis in males, whereas breast cancer is the most common source in females.
Besides the following symptoms, many patients will have experienced symptoms caused by the original tumor and its related manifestations.
Increased Intracranial Pressure. In most of the patients, the symptoms of brain metastases are those of expanding (growing) mass lesions and increased intracranial pressure (ICP-the pressure within the skull). The most common symptoms, or "generalized manifestations" of increased ICP are headache, vomiting, and disturbance of consciousness.
Headache. Headache is the initial symptom in about half of brain tumor patients, and is eventually experienced by the majority of these patients at some point.
Vomiting. Vomiting is an occasional accompaniment to the headache. It is a far more common occurrence in children than in adults. In children, vomiting may be especially dramatic and forceful, so much so that it has been called "projectile" in nature.
Alteration in Consciousness. Brain tumor patients at some points commonly experience alterations in consciousness, including both the level of consciousness and/or its quality. A brain tumor can induce a wide spectrum of changes in mental status ranging from subtle alterations in personality to states of profound and irretrievable coma.
Fits (Epileptic Seizures). Fits are associated with brain tumors in almost 35 percent of brain tumor patients. Age increases the risk of epilepsy being caused by a tumor especially in individuals beyond 45 years of age.
Focal (Specific) Neurological Symptoms. Whereas headaches, altered mental status and seizures may be seen with tumors that occur in many parts of the brain, some symptoms are associated with tumors that occur in specific locations. These focal neurological symptoms affect the side of the body opposite from the side where the tumor resides and include different modalities of sensation, such as tingling, and motor changes, such as weakness (hemiparesis).
Brain metastasis can be diagnosed by the following diagnostic tests:
CAT Scan (Computed Axial Tomography; also called a CT scan): A CAT scan can be done with or without contrast (dye given to the patient intravenously before the study for better visualization of the tumor) with different views.
MRI (Magnetic Resonance Imaging) also known as NMR: It makes a clear picture of the brain using powerful magnets and radio waves. With the addition of a contrast agent given intravenously, this is the single best tool for radiographic evaluation of brain metastasis.
In addition to the above two diagnostic tests, the treating neuro-oncologist or neurosurgeon can ask for further sophisticated studies.
Treatment varies with the size and type of the tumor, primary site of the tumor, and the general health of the person. Among the goals of treatment may be relief of symptoms, improved functioning, or comfort.
Non-chemotherapeutic drugs: These drugs are given to relieve pain, such as headache pain, control epilepsy, and diminish swelling (edema) of the tumor.Examples of these drugs are analgesics, phenytoin and cortisone.
Chemotherapeutic drugs: These drugs are designed to attack and kill cells that divide rapidly, such as cancer cells. Chemotherapy can treat the whole brain. Additionally, multiple cancer sites can be treated at the same time.
Surgery is an important part of the management for some patients with brain metastasis. During surgery, first tissue is obtained to confirm the diagnosis. Then the tumor, also called a lesion, is removed. Surgery is performed when the treating physician determines that it is likely to lead to greater relief of symptoms than might be achieved by other treatments and it possibly can extend survival.
Another treatment approach uses radiation to destroy cancer cells. Like chemotherapy, radiotherapy can be given to the whole brain (WBRT, or whole brain radiotherapy) in fractionated (divided) doses. Stereotactic radiosurgery (SRS), a great advance in radiotherapy, uses a three-dimensional technique to target a single large dose of radiation with either a gamma knife or a linear accelerator. Its main advantage is its ability to treat lesions that are not easily treated by surgery. Also, it is not invasive, has fewer risks and results in shorter hospital stay.
Other types of treatment
New trials are being performed to use gene therapy for treatment of metastasis. However, gene therapy for brain metastasis is still in its infancy.
In general, the probable outcome is fairly poor. Many people with metastatic brain tumors have widespread tumor metastsis. Death often occurs within two years. The prognostic factors are complex and largely depend upon the status of systemic disease, extent of neurological deficit, length of time between first diagnosis of cancer and the diagnosis of brain metastsis, the type of primary (original) tumor, and the nature, size, and invasiveness of the metastatic lesion, among other factors.
Bahaa E. Hafez, MD, is a post-doctoral fellow at the University of Texas in Houston and Instructor of neurosurgery, Faculty of Medicine, Menofyia University, Shebin,El-kom, Egypte.