What Is a Brain Metastasis and Why Does It Occur?
A brain metastasis arises when cells from a malignant tumor elsewhere in the body travel through the bloodstream to the brain and form new foci there. The most common source is lung cancer; this is followed by breast cancer, melanoma (skin cancer), and kidney and colon cancers. Metastases usually settle at the grey-white matter junction of the brain, may be single or multiple, and tend to create marked oedema around them. In some patients a brain metastasis appears as the first sign of an as-yet-unknown cancer; in that case a whole-body scan is needed to find the source tumor. A diagnosis of brain metastasis does not turn into a meaningful treatment plan unless it is assessed together with the type and stage of the primary cancer.
Symptoms and Diagnosis
Symptoms vary with the location of the metastasis and the oedema it causes: an increasing headache, nausea and vomiting, a first-ever seizure, limb weakness or sensory loss matching the compressed region, speech and balance disturbances, visual problems, and changes in consciousness and behaviour can occur. Contrast-enhanced brain MRI is the most sensitive method in diagnosis; metastases typically appear as ring-enhancing lesions with wide surrounding oedema, often multifocal. In a patient with a known cancer, imaging is usually enough for diagnosis; for a single lesion of uncertain source, a biopsy may be needed to distinguish it from a primary brain tumor. At the same time the whole body is scanned with PET-CT and the extent of disease is determined.
Treatment Options: Surgery, Gamma Knife and Drug Therapies
There is no single 'right' treatment in brain metastasis; the choice is made according to the number and size of metastases, their location, the symptoms and the status of systemic disease. For a single or few large, symptomatic metastases, surgery comes to the fore: the tumor is removed, compression and oedema fall rapidly, and a definitive tissue diagnosis is obtained; surgery is usually followed by radiosurgery to the tumor bed. For small or multiple metastases (usually from a few to a few dozen), stereotactic radiosurgery (Gamma Knife, CyberKnife) is preferred; in a single session it treats the target with focused high-dose radiation while largely sparing healthy tissue. In very widespread disease, whole-brain radiotherapy may come into consideration, but is used more selectively today because of its cognitive side effects. In some cancer types (for example certain lung and breast subtypes, and melanoma), targeted drugs and immunotherapy that can cross into the brain have moved to the centre of treatment. The decision is always a team decision made jointly by the neurosurgeon, radiation oncologist and medical oncologist.
The Surgical Process and Recovery
In a patient planned for surgery, preparation includes contrast MRI, systemic staging, steroids to reduce oedema and, when needed, antiseizure medication, along with an anaesthetic assessment. In surgery the patient is positioned according to the metastasis location, a narrow shave within the hairline is sufficient, the bone flap is lifted, and the metastasis is removed under the microscope with neuronavigation; for locations near functional areas, mapping and, where needed, an awake technique may be used. Because metastases are usually relatively well demarcated from brain tissue, a marked reduction and rapid relief of symptoms can be achieved in a suitable case. After surgery there is usually a short stay in intensive care and a few days in hospital; recovery varies with the person's general condition and the systemic treatment plan. In most patients radiosurgery to the operative bed is added afterwards to reduce recurrence.
Realistic Expectations and Quality of Life
The aim of treatment in brain metastasis must be discussed honestly: this is in most cases part of an advanced-stage cancer, and the goal of treatment is usually to keep the disease under control, relieve brain-related symptoms (headache, seizures, weakness) and preserve quality of life. Even so, long-term disease control may be possible in selected patients with a limited number of metastases whose primary cancer is well controlled; not every patient is the same. Survival and response vary markedly according to the type and molecular features of the cancer, the number of metastases, the patient's performance and the response to systemic therapy. We make no promise of a guaranteed outcome. Control of pain and seizures, steroid management, nutrition and psychological support are also inseparable parts of treatment; planning is done realistically and compassionately, in open communication with the patient and family.