Definition:

Neoplastic meningitis (NM) is a diffuse dissemination of tumor cells into the cerebrospinal fluid (CSF) and/or leptomeninges. NM is reported in patients with solid tumours (carcinomatous meningitis), haematological malignancies (leukaemic or lymphomatous meningitis), or primary brain tumours. Malignant cells reach the CSF and meninges by direct invasion from tumors located near or within the central nervous system (CNS), or via the bloodstream or other pathways that contact the CNS. The molecular changes responsible for the development of NM are not well delineated, but it is likely that they involve changes in molecules responsible for tumor cell adhesion, migration, and proliferation.