White matter: The part of the brain inside the cortex (the wrinkled gray matter). White matter consists of glial cells, nerves, and axons that transmit impulses.
WHO tumor grading: The standard established by the World Health Organization (WHO) to rate tumors.
- Grade I tumors are slow-growing, nonmalignant, and associated with long-term survival.
- Grade II tumors are relatively slow-growing but sometimes recur as higher grade tumors. They can be nonmalignant or malignant.
- Grade III tumors are malignant and often recur as higher grade tumors.
- Grade IV tumors reproduce rapidly and are very aggressive malignant tumors.
