Of the different types of cystic tumor originating within the third ventricle (aside from cystic degeneration of a solid tumor and the epidermoid, the dermoid and the parasitic cyst), that containing colloid material arising from the most rostral end of the roof of the third ventricle is by far the most interesting and important. This cystic tumor, because of its distinct gross and microscopic appearance, has largely been referred to in the literature as "colloid cyst," and recently, because of the as yet uncertain origin and the nature of the content, it has been called "neuro-epithelial cyst" by Percival Bailey.
The frequent reports of cases of this cystic tumor in the recent literature are probably due to increasing knowledge of its clinical manifestations, to the almost pathognomonic significance of ventricular air studies (Dandy1 and Davidoff and Dyke2) and to the successful surgical treatment (Dandy,1 Davidoff and Dyke,