n. a tumor composed only of neuroglial cells (see neuroglia). The tumor is provided a classification from Grade 1 to Grade IV according to the severity and rate of growth. Grade II tumors are also called astroblastomas- Grade III and IV tumors are often known as glioblastoma. Grade I tumors may be associated with minimal behavioral or cognitive impacts, but larger and faster growing tumors may lead to severe impairment in functioning depending on their location within the brain.