Lymphomatous meningitis is the spread of lymphoma to the leptomeninges, either around the brain, spinal cord, or nerve roots. This can occur either as a focal area or diffusely along the meninges. Symptoms include headache, radicular pain, cranial nerve dysfunction, or symptoms of spinal cord dysfunction. Seizures are a rare presentation. Communicating hydrocephalus and subsequent increased intracranial pressure is a potential complication of lymphomatous meningitis, which can add significant morbidity.

In contrast to infectious meningitis, fever is often absent. Leptomeningeal involvement can occur both in lymphomas primary to the central nervous system (CNS) and in systemic lymphoma secondarily invading the CNS. Lymphomas rarely begin in the leptomeninges. Presence of leptomeningeal involvement of the lymphoma may affect prognosis and treatment decisions and typically carries a poor prognosis.