Carcinomatous meningitis results from the spread of cancer cells into the leptomeninges, the subarachnoid space surrounding the brain and spinal cord. It typically occurs from metastasis of neoplastic cells from a primary tumor site, mostly commonly breast or lung cancer or melanoma, and occurs in 5% of patients with these cancers. Carcinomatous meningitis can also occur after seeding of the subarachnoid space from a primary brain tumor such as a medulloblastoma. Rarely, primary diffuse meningeal melanomatosis can occur.

Symptoms include headache, neck or back pain, altered mental status, seizures, weakness, and sensory disturbances. Fever is typically absent. Multiple cranial neuropathies, particularly in a patient with a known cancer diagnosis, should raise concerns for this condition. Prognosis is poor, and median survival with treatment is less than 6 months.