The diagnostic classification, astrocytoma, broadly embraces the many varieties and grades of astrocytic neoplasms including the glioblastoma multiforme. While it may be argued that gliomatosis cerebri is a pattern of spread or a tumor of uncertain histologic origin, the vast majority exhibit astrocytic features and thus the discussion of gliomatosis is included with the astrocytic tumors. The pituicytoma, while of astrocytic origin, is included in the discussion of tumors of the sellar. The astroblastoma, considered to be of uncertain origin but showing ultrastructural features of tanycytes, is discussed separately as is the chordoid glioma of the III ventricle. The remaining tumor considered to be of uncertain origin is the polar spongioblastoma, which we consider to be more akin to a growth pattern than a specific histologic type and to occur possibly in either gliomas or tumors of neuronal origin (Schiffer et al., 1993).