Epithelial cyst of the fourth ventricle. Case report. A case of epithelial cyst in the fourth ventricle of a 4-year-old child is described. A single epithelial layer with a clear basement membrane lining the cyst wall was observed. There were no prominent histological findings to suggest a pathogenesis for this cyst based on immunohistochemical or ultrastructural studies; however, the cyst fluid contained significant amounts of carcinoembryonic antigen. It is considered that the epithelial layer lining the cyst wall was possibly of endodermal origin. 