Cytologic composition of the untreated glioblastoma with implications for evaluation of needle biopsies.

To study the progression of astrocytic neoplasms and to provide practical information about the topography of the glioblastoma multiforme, the distribution of eight defined cell types was mapped from whole brain sections of 18 glioblastomas studied postmortem. Based on the densities and topographic distributions of well-differentiated and anaplastic cells, three principal categories of neoplasms were defined. In one group of three cases, multifocal glioblastomas appeared to be emerging in the background of a better differentiated, and presumably precursory, astrocytic neoplasm. In another group of nine cases, the neoplasms were more intimate mixtures of well and poorly differentiated cells. The third group of five cases was composed of neoplasms that were largely undifferentiated without a component of better differentiated cells. The study suggests that progression from a better differentiated neoplasm to one composed largely of undifferentiated cells is common in the fibrillary astrocytic neoplasms. Although some glioblastomas appear largely undifferentiated and consistent with the de novo appearance of overt malignancy, the size of these neoplasms and the patterns of necrosis leave open the possibility that a preexisting better differentiated neoplasm had been obliterated by necrosis and the overgrowth of the anaplastic component. The potential topographic variation of cellular constituency in a glioblastoma underscores the care that must be exercised in utilization of the needle biopsy technique in the diagnosis and grading of astrocytic neoplasms.