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.

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