After primary central nervous system (CNS) lymphoma has been diagnosed, tests are done to find out if cancer cells have spread within the brain and spinal cord or to other parts of the body. When primary CNS lymphoma continues to grow, it usually does not spread beyond the central nervous system or the eye. The process used to find out whether cancer has spread is called staging. The following tests and procedures may be used in the staging process:

• CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography. For primary CNS lymphoma, a CT scan is done of the chest, abdomen, and pelvis (the part of the body between the hips).
• Bone marrow biopsy: The removal of a small piece of bone and bone marrow by inserting a needle into the hipbone or breastbone. A pathologist views both the bone and the bone marrow samples under a microscope to look for signs of cancer.
• Slit-lamp eye exam: An exam that uses a special microscope with a bright, narrow slit of light to check the outside and inside of the eye.
• Vitrectomy: A surgical procedure to remove some or all of the vitreous humor (the gel-like fluid inside the eyeball). The fluid is removed through tiny incisions and then viewed under a microscope by a pathologist to check for cancer cells.