As many as 25% of all patients with cancer develop metastasis to the brain or spinal cord, and the disease becomes clinically significant in most patients. As the population in general lives longer and as other therapies become more successful in controlling disease outside the CNS, it is likely that the incidence of CNS metastases will increase.

PATHOLOGY

The most common primary sites of metastases to the CNS are the lung and breast, metastases from the lung being more frequent overall because of the larger numbers of patients with this malignancy. Other common primary sites include melanoma from any site, leukemia and lymphoma, and renal cancers. Virtually any primary cancer may spread to the CNS with involvement of brain and spinal cord parenchyma, leptomeninges, dura, and pituitary gland.

Lung cancer is the most common primary source of brain parenchymal metastases, and of the various forms of lung cancer, small-cell tumors are the most likely to metastasize. Metastasis to the dura, in contrast, arises more frequently from cancer of the breast or prostate or lymphoma. Leptomeningeal disease occurs frequently as a consequence of cancer of the breast, lung, and melanoma, as well as lymphoma and leukemia. Breast cancer is the most frequent tumor to metastasize to the pituitary gland.

CLINICAL PRESENTATION

The signs and symptoms of intracranial metastases are identical to those of primary brain tumors and are thus indistinguishable. Patients present with signs and symptoms related to the location of the lesion or with more generalized signs such as personality changes, headache, generalized seizures, or weakness; dexamethasone is useful for diminishing peritumoral edema that may contribute greatly to the symptoms. An initial manifestation as a brain tumor is common for lung cancer but rare for other cancers. Every adult with symptoms of a brain tumor should have a CT scan of the lungs because plain x-ray films of the chest may not reveal small pulmonary lesions that could be the primary neoplasm. Acute findings may be the result of hemorrhage into the tumor and may be caused by hydrocephalus or by acute increases in intracranial pressure. Leptomeningeal findings include more general symptoms, such as headache and nausea, or more specific signs and symptoms related to the area most affected, such as lower cranial nerve involvement (oculomotor or facial nerve) or lower spinal nerve invasion causing weakness, reflex changes, and bowel and bladder dysfunction. Dissemination of the tumor into the CSF (carcinomatous, lymphomatous, or leukemic meningitis) may produce hydrocephalus and may cause nuchal rigidity. Involvement of the dura may produce symptoms of pain and specific nerve root compression. Pain over the site of the metastasis or pain radiating in a nerve root pattern is the most common clinical finding associated with epidural spinal metastasis.

DIAGNOSIS

Of the parenchymal lesions, approximately 50% are solitary metastases.. In the absence of a recognized primary tumor, the diagnosis must be verified histologically. With a known primary tumor, either before or after it is treated and in the absence of obvious systemic dissemination, we do not assume a metastatic origin but rather advocate stereotactic needle biopsy of a solitary brain tumor. In cases of a known systemic primary lesion, multiple lesions in the brain almost certainly are due to metastatic disease, and a presumptive diagnosis of metastatic tumor to the brain would be warranted.

Radiographic findings of intracranial metastases include contrast-enhancing single or multiple lesions.. In general, metastatic brain tumors are surrounded by a large area of edema. Hemorrhage may occur and, if extensive, can obscure the tumor. Some tumors have central areas of necrosis that do not enhance, or the entire lesion may enhance uniformly with sharply demarcated borders. MRI-Gd may be more sensitive than CT because it can visualize smaller lesions and view the posterior fossa free of the bone artifacts observed with CT. Areas of abnormal enhancement along the dura or leptomeninges are also better visualized with MRI-Gd (228). If contrast-enhanced CT reveals one lesion, we routinely follow CT with MRI-Gd to exclude other lesions. MRI of the spine, with and without Gd, is the first diagnostic test used to assess the spinal compartment.