The Gliomas Roentgenologically Considered

IN order to be able intelligently to consider the gliomas from a roentgenologic viewpoint, we should first review briefly our present beliefs regarding the origin of these tumors and their development as pathologic entities. There are still differences of opinion as to the origin and classification of the gliomas, but it seems fairly safe to say that they originate from brain tissue which in some way has been stimulated to abnormal growth. There are many theories regarding the origin of gliomas which have been suggested from time to time by such well-known authorities as Cohnheim, Samuel, Monakow, Pfleger, Bailey, and others. Pfleger, as quoted by Bailey, has shown that in 75 out of 400 cerebellums that he studied he was able to find incompletely differentiated cells close to the roof of the fourth ventricle, which is a common site for the development of the medulloblastomas. This is a rather suggestive finding. Cohnheim's theory attempts to explain the origin of the gliomas from undifferentiated cells, but del Rio Hortega has shown that in many instances in which undifferentiated cells were thought to be present, actually the cells were quite well developed. It seems highly probable that the origin of the gliomas is not essentially different from the origin of tumors elsewhere in the body, and that they arise from some “anlage” composed of cells capable of unrestricted growth when subjected to a suitable stimulus. If this is true, then we must conclude that these tumors are potentially present at birth in those persons who eventually develop such lesions. As a corollary to this assumption, we might be tempted to suggest radiotherapy for all, after the brain has become completely developed, in the hope that the tumor anlage is radiosensitive. We know brain tissue is extremely radioresistant so that such radiation would be harmless, and any harmless procedure which might reduce the prevalence of brain tumors would certainly be worth considering. Many attempts have been made to classify the gliomas according to the cell types of which they are composed. Certainly one of the most successful of these efforts was that of Bailey and Cushing whose classification is, I believe, the most widely accepted of any to date. Briefly, their schema traces the development of the various tumors from the original medullary epithelium through the many cell differentiations, each giving potential origin to a particular type of tumor, and finally to the highly differentiated portions of the brain from which other types of tumors arise. This is well portrayed in Figure 1; from this chart it can be seen how the rather formidable nomenclature of the gliomas has been devised. Before considering these tumors individually, it might be well to point out that brain tumors are by no means as uncommon as some are wont to believe.