Brain metastases are cancers that originate in another part of the body that spread to and grow in the brain. The original site of the cancer is known as the primary site. Approximately 20% of brain metastases consist of a single lesion. The rest of the cases involve multiple lesions in the brain.
Brain metastases are typically irritating to the brain, causing swelling (edema). The swelling is responsible for common symptoms, which include:
- Vision changes
- Upper and lower extremity weakness
- Speech difficulties
Cancer patients who have any neurological symptoms usually undergo an MRI scan of the brain to rule out a brain metastasis.
An MRI scan of the brain is the most sensitive imaging test to identify brain metastases. A CT scan is possible if the patient cannot have an MRI scan, but does not usually provide as detailed information. Occasionally, a PET scan (nuclear imaging) can reveal a brain metastasis. It is not uncommon to discover brain metastases during a staging work-up for a patient’s primary cancer.
Patients who are identified to have brain metastases are often started on steroids (Decadron) for symptomatic relief. Definitive treatment options include surgical resection, radiation therapy, and stereotactic radiosurgery. Surgery is usually reserved for patients who have very large lesions or if they are found to have a lesion with an unknown primary site. Surgery would then allow for tissue sampling for biopsy, which can identify the primary site of the tumor. Otherwise, stereotactic radiosurgery (gamma knife) is a very effective treatment for either single or multiple metastases. Whole brain radiation (WBR) is frequently used for patients as an adjunct to surgery. In some cases, whole brain radiation is used as a solo modality. More recently, stereotactic radiosurgery alone is being used for patients who have three or fewer metastases.
Most patients with brain metastases from primary cancers are eligible for one of several treatment modalities. In most cases, the brain disease can be controlled with treatment.