Primary central nervous system (CNS) lymphoma (PCNSL) is a rare form of non-Hodgkin lymphoma (NHL). PCNSL starts in B cells (a type of white blood cell). It does not spread outside the central nervous system (CNS). Most PCNSLs are intermediate to high grade.
PCNSL occurs most often in the cerebral hemisphere but may involve the cerebrospinal fluid, vitreous humor (jelly-like substance in the centre of the eye), meninges and other places within the brain and spinal cord. PCNSL may be found in several places because it has the potential to spread throughout the central nervous system.