The tumor is usually solid, although cysts may be present. Rarely the tumor consists of a solitary cyst and mural nodule. Grading according to degree of malignancy was first proposed in 1949. In this classification, astrocytomas and glioblastomas represent different grades of malignancy of the same tumor. Grade I tumors, typically slow growing, are characterized by most cells having normal characteristics, and few mitotic features.
Endothelial proliferation is absent.
There is no clear line of demarcation from normal tissue. Grade III tumors represent anaplastic astrocytomas and Grade IV tumors represent the typical glioblastoma multiforme, characterized by cellular pleomorphism, vascular proliferation, mitoses, and multinucleated giant cells. In adults, glioblastomas are noted most frequently in the frontal lobe with the temporal lobe second in frequency. Primary glioblastoma of the spinal cord in childhood is rare. Glioblastoma multiforme in children appears to have two characteristic courses, each of which is related to the location of the tumor.