Walsh & Hoyt: Colloid Cysts of the 3rd Ventricle

There has been a great deal of controversy regarding the origin of colloid cysts. At the heart of the controversy is whether the cysts are of neuroepithelial or endodermal origin. Some investigators favor a neuroepithelial origin, suggesting that the paraphysis forms what is essentially an extraventricular portion of the choroid plexus derived from primitive neuroectoderm of the roof of the diencephalon. Cyst formation is thus ascribed to abnormal foldings of neuroectoderm with subsequent separation of the folds. The results of electron microscopic studies support the concept of a neuroepithelial origin for the colloid cyst. Other investigators believe that colloid cysts are of endodermal origin and cite architectural, cytologic, and immunohistochemical data to support this theory. Although there is strong evidence that colloid cysts are of endodermal origin, we have chosen to include them in this chapter for the sake of completeness.