Brain metastasis occurs in many patients and its rate is about 20-40%. Because no national cancer registry documents brain metastases, the exact incidence is unknown, but it has been estimated that 98,000 to 170,000 new cases are diagnosed in the

The most common primary cancers metastasizing to the brain are lung cancer (50%), breast cancer (15%-20%), unknown primary cancer (10%-15%), melanoma (10%), and colon cancer (5%). Eighty percent of brain metastases occur in the cerebral hemispheres, 15% occur in the cerebellum, and 5% occur in the brain stem. Metastases to the brain are multiple in more than 70% of cases, but solitary metastases also occur. Brain involvement can occur with cancers of the nasopharyngeal region by direct extension along the cranial nerves or through the foramina at the base of the skull. Dural metastases may constitute as much as 9% of total CNS metastases.

A lesion in the brain should not be assumed to be a metastasis just because a patient has had a previous cancer; such an assumption could result in overlooking appropriate treatment of a curable tumor. Primary brain tumors rarely spread to other areas of the body, but they can spread to other parts of the brain and to the spinal axis.

The diagnosis of brain metastases in cancer patients is based on patient history, neurological examination, and diagnostic procedures. Patients may describe headaches, weakness, seizures, sensory defects, or gait problems. Often, family members or friends may notice lethargy, emotional liability, or personality change.

A physical examination may show objective neurological findings or only minor cognitive changes. The presence of multiple lesions and a high predilection of tumor may be sufficient to make the diagnosis of metastases. In the case of a solitary lesion or a questionable relationship to the primary tumor, a brain biopsy (usually a stereotactic biopsy) may be necessary. In one study, the diagnosis of single brain metastasis was changed in 6 of 54 patients after the lesion was biopsied. The 6 patients had primary brain tumors or infectious and inflammatory lesions. CT scans with contrast or MRIs with gadolinium are quite sensitive in diagnosing the presence of metastases. PET scanning and spectroscopic evaluation are new strategies to diagnose cerebral metastases and to differentiate the metastases from other intracranial lesions.

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