Abstract
Five colloid cysts of the third ventricle were compared with two spinal enterogenous cysts to examine the hypothesis that these entities have the same origin from primitive endodermal tissue. All the lesions showed cuboidal and columnar epithelium with mucus containing goblet cells and cilia. Immunohistochemistry for cytokeratin, EMA and CEA was positive in all the colloid cyst and enterogenous cyst epithelium. S-100 was focally positive in three of the colloid and one of the enterogenous cysts while vimentin and GFAP were negative in both. The anatomical distribution of both colloid and enterogenous cysts is reviewed. An illustrative case of an identical cyst within the fourth ventricle is presented. This suggests that the similarities between colloid and enterogenous cysts and the presence of identical lesions along the neuroaxis indicate that these structures are derived from primitive foregut endoderm.