Mixed Gliomas

Abstract

The subject of mixed glial neoplasms has continued to be a source of considerable debate. Most people recognize that a glial neoplasm may show phenotypic features of more than one glioma type, most commonly a mixture of astrocytoma and oligodendroglioma (oligoastrocytoma). The major question arises, however, as to exactly what point one crosses the threshold in designating the lesion as mixed as opposed to calling it a pure glioma. Unfortunately, the literature has not been terribly helpful in this arena; many of the articles that have dealt with the subject have not specifically defined what is meant by a mixed glioma and those that do, do so somewhat arbitrarily, resulting in a lack of uniformity or agreement. Precise guidelines as to what percentage of a second glial component one needs to see in order to designate a tumor as “mixed” remains unclear. In the single largest series of mixed gliomas published to date, written over twenty years ago, mixed gliomas were simply defined as tumors of the brain and spinal cord comprised of two or more neoplastic counterparts of the normal glial cellular constituents of the central nervous system, without further specification with regard to how much of a second component one needed to see in order to designate the lesion as “mixed glioma” (1).