A

Adjuvant therapy: Cancer treatment added to the main treatment, often to keep cancer from returning. 

Audiologist: A health care professional who conducts detailed tests to detect and assess hearing loss. 

B

Benign tumor: A slow-growing tumor that isn't cancerous and that is less likely to invade normal tissue. Benign tumors can still pose a threat in the brain or spinal cord, however, because they can press on vital structures.

Biopsy: The removal of tissue from in and around a tumor so a pathologist can examine it under a microscope. How the cells look indicates whether the tumor is cancer and how fast it is likely to grow. A biopsy is usually the only way to diagnose a brain or spinal cord tumor's type.

C

Cancer: A collection of abnormal, rapidly dividing cells that can invade normal tissue and spread to other parts of the body. (Cancer in the brain or spinal cord sometimes spreads to another part of the brain or spinal cord but rarely spreads outside the central nervous system.)

Cell: The building block of all life forms, each containing the body’s genetic code and the ability to replicate.

Central nervous system: The brain and spinal cord.

Cerebrospinal fluid, or CSF: Clear liquid that flows in and around the brain and spinal cord to cushion them against injury, to transfer nutrients and to remove waste.

Chemotherapy: Treatment that uses medications to kill tumor cells.

Clinical trial: A research study that tests a therapy, device or technique on patients. The goal is generally to improve the prevention, detection or treatment of a condition.

CNS: An acronym for central nervous system.

Cranium: The skull, especially the part that encloses the brain.

D

Differentiation: The process by which cells mature and develop distinct features. Normal cells become "well-differentiated." Tumors with cells that are "undifferentiated" or "poorly differentiated" are more likely to be fast-growing and invasive.

Diffuse: Widely spread.

E

Endocrinologist: A doctor who treats disorders of the endocrine system — the glands that make the hormones that regulate growth, metabolism, reproduction and other functions.

F

Fractionated radiation: Radiation therapy that’s split into sessions over several weeks to reduce side effects and to give normal cells time to repair themselves.

H

High-grade tumor: A cancerous tumor that is fast-growing and invasive.

I

Immunotherapy: Treatment that seeks to harness the body’s immune system to fight cancer.

Intraoperative MRI, or iMRI: A magnetic resonance imaging scanner used during surgery.

L

Lesion: An area of abnormal tissue, sometimes because of damage from disease or injury.

Localized: Confined to one part of the body.Low-grade tumor: A tumor that’s benign, slow-growing and less likely to spread or to invade normal tissue.

M

Malignant tumor: A tumor that is cancerous and more likely to spread and to invade normal tissue. Malignant tumors are usually high-grade tumors.

Metastatic tumor: A tumor that has spread from a tumor elsewhere in the body.

Metastasize: The process by which tumor cells spread in the body, usually through the bloodstream, lymph system or cerebrospinal fluid. (Brain and spinal cord tumors rarely spread outside the central nervous system but sometimes spread to another part of the brain or spinal cord.)

MRI scan: A detailed image of structures inside the body made with an MRI scanner. MRI, an acronym for magnetic resonance imaging, uses radio waves (not X-rays), a large magnet and a computer.

N

Nervous system: The network of nerves that transmit information among the body’s parts. The brain and spinal cord form the central nervous system. Nerves in the rest of the body form the peripheral nervous system.

Neoplasm: A tumor.

Necrosis: The process by which body tissue dies because of disease, injury or lack of blood supply. Necrosis can also describe an area of dead tissue.

Neuron: The cells in the brain and spinal cord that transmit information using electrochemical signals. Also called nerve cells.

Neurologist: A doctor who treats conditions of the nervous system.

Neuro-oncologist: A doctor who directs the treatment of brain and spinal cord tumors and who delivers chemotherapy.

Neuro-ophthalmologist: A doctor who diagnoses and treats vision problems caused by a condition of the brain, spinal cord or another part of the nervous system.

Neuropathologist: A doctor who analyzes tissue to identify diseases of the nervous system.

Neurosurgeon: A doctor who treats conditions of the brain and spinal cord using surgery.

O

Oncologist: A doctor who treats cancer.

Ophthalmologist: A doctor who treats eye conditions and vision problems.

P

Palliative care: Treatment to control symptoms and to provide comfort to patients with a life-threatening condition.

Pathologist: A doctor who analyzes tissue and body fluids to identify a disease or condition.

Pediatric neuro-oncologist: A doctor who directs treatment of brain and spinal cord tumors in children and teens; who fills the role of pediatrician on the patient's care team; and who delivers chemotherapy.

Pediatric neurologist: A doctor who treats conditions of the nervous system in children and teens.

Pediatric neurosurgeon: A doctor who treats conditions of the brain and spinal cord in children and teens using surgery.

Peripheral nervous system: The collection of nerves that transmit messages between the central nervous system — the brain and spinal cord — and the rest of the body.

Posterior fossa: A cavity in the lower back of the skull that encases the brain's cerebellum and brain stem. 

Precision or personalized medicine: An emerging treatment approach that tailors therapies to a tumor's genetic characteristics.

Primary tumor: A tumor found where it developed. This term can also refer to the original tumor or to the biggest tumor.

Progression: Advancement of disease. With brain and spinal cord tumors, this often refers to growth of a residual tumor, or the part of a tumor that remains after treatment.

R

Radiation oncologist: A doctor who treats cancer with radiation therapy.

Radiologist: A doctor who uses imaging, such as X-rays and MRI scans, to diagnose conditions.

Radiation therapy: The use of radiation to fight cancer or a tumor or tumors.

Recurrence: The return of a tumor after it was undetectable for a time following treatment.

Refractory cancer: Cancer that is resistant to treatment.

Remission: The disappearance or significant reduction of a tumor and/or symptoms. A remission can be complete or partial, permanent or temporary.

Resection: The surgical removal of all or part of a tumor.

Residual tumor: The part of a tumor that remains after treatment. This could include, for example, the part of a tumor that could not be surgically removed.

S

Secondary tumor: A tumor that spread from elsewhere in the body or that is smaller than the primary, or main, tumor.

Shunt: A system that uses flexible tubing and a valve to drain fluid from one part of the body to another.

Solid tumor: A mass of abnormal cells, often without liquid areas. Tumors are identified as solid to differentiate them from blood cancers such as leukemia.

T

Tumor: A mass of abnormal cells.

Tumor grades: A four-tier system of classifying tumors based on how the cells look under a microscope. Grade I and II tumors are typically benign (not cancer), slower-growing and less likely to be invasive. Grade III and IV tumors are malignant (cancer), faster-growing and invasive.

Tumor stages: A system of classifying how serious tumors are based on their size, location, grade and whether they have spread. With brain and spinal cord tumors, the extent of spread is the key factor.

V

Ventricles: A network of four interconnected cavities in the brain that are filled with cerebrospinal fluid, the liquid that cushions the brain and spinal cord against injury.

• Dictionary of Cancer Terms, National Cancer Institute
• Brain Tumor Education, American Brain Tumor Association