Primary Intraventricular Tumors

Abstract

Intracranial tumors which are primarily of intraventricular origin are exceedingly rare, and by primary intraventricular tumors we mean those arising from cells which normally line the ventricles, i.e., ependymal cells and those of the choroid plexus. We do not include tumors which originate elsewhere and project into the ventricles, or those such as epidermoids and meningiomas which develop within the ventricles from cell rests. Ependymomas comprise only a small percentage of the intracranial neoplasms reported by Bailey and Cushing, 3 per cent (3); Bennett, 3 per cent (4); Ringertz and Reymond, 6 per cent (18); Zülch, 4 per cent (25); and Svien, 9 per cent (22). Tumors arising from the lining cells of the choroid plexus are even more rare, forming but 0.6 per cent of Bailey and Cushing's cases, 1 per cent of Ringertz and Reymond's, and 0.5 per cent of Zülch's series. Considerable controversy is encountered in the literature as to the pathological classification of ependymomas. Virchow is credited by Zülch with first describing an ependymoma in 1863 (25). Mallory, in 1902, described cytoplasmic granules within the cells of certain gliomas which he called blephoroplasts, thereby indicating that these tumors were of ependymal origin. Bailey and Cushing in 1924 and 1926 were the first to separate and define as a specific pathological entity tumors which arose from ependyma (2, 3). Kernohan in 1937 (11) divided the ependymomas into epithelial, myxopapillary, and cellular types. Although of some benefit for descriptive purposes, this classification is of little value in estimating biologic activity inasmuch as biologic behavior depends more upon the degree of cellular anaplasia than upon cell type. Classification upon the latter basis, therefore, has failed to find favor with many pathologists, who prefer a simpler division of ependymal tumors into benign and malignant types. A further difficulty in classification arises in some of the more malignant and undifferentiated tumors, where it is almost impossible to determine with certainty whether the lesion is primarily of ependymal origin or is a glioma including ependymal elements which are not actually contributing to its growth. Tumors of the subependymal glia may project into the ventricle and include ependymal elements which make a definite differentiation difficult if not impossible. Within any series, however, there are only a few cases in which such difficulty in classification will arise, and about which there might be dispute among pathologists. These are probably statistically unimportant, but they do give rise to some uncertainty when series from different clinics are compared. Similar controversy has been encountered in the classification of choroid plexus papillomas. Davis and Cushing (6) differentiated papillomas from the papillary type of ependymoma.