IV. Metastatic Neoplasms
A. Incidence: adults (about half of CNS tumors in adults are metastatic); incidence varies with primary tumor
B. Origin: hematogenous spread from neoplasms in the body, especially from lung and breast tumors and malignant melanomas
C. Location: multiple sites are common, but there may be a single focus of a metastatic neoplasm; junction between cortex and underlying white matter most common, but metastases may occur anywhere in the brain. Also, diffuse meningeal infiltration (carcinomatous meningitis) may occur (see image at right).