Asymptomatic and Symptomatic Rathke's Cleft Cysts: Histological Study of 45 Cases

Pituitary cysts are fairly often found incidentally in anatomical studies, but symptomatic cysts are relatively uncommon. In this study, the histological characteristics of 42 asymptomatic and three symptomatic Rathke's cleft cysts were examined and compared. The 42 cysts found incidentally at autopsy were classified as small (less than 1 mm in diameter), medium (1 to 5 mm), or large (over 5 mm). There were 23 small (55%), 13 medium (31%), and six large (14%) cysts. The mean ages of the three patient groups were 66, 60, and 53 years, respectively. Flattened epithelial cells were the most common cells in small cysts, while cuboidal to columnar epithelial cells were more prevalent in medium and large cysts. The larger cysts tended to contain cilia. The three symptomatic cysts were histologically confirmed to be Rathke's cleft cysts by their characteristic ciliated columnar epithelial lining. No essential histological differences were observed between asymptomatic and symptomatic cysts, and the mechanism of change from asymptomatic to symptomatic Rathke's cleft cyst was not clarified. Small nests of epithelium at the junction of the pars tuberalis and pituitary stalk are considered to be remnants of Rathke's pouch and are thought to give rise to craniopharyngioma. In their most typical forms, Rathke's cleft cysts and craniopharyngiomas are histologically distinguishable, craniopharyngiomas being composed of stratified squamous epithelium and simple Rathke's cleft cysts of a layer of cuboidal or columnar epithelium on a basement membrane. It is believed that the most important difference is that Rathke's cleft cyst is a simple cystic enlargement and does not undergo the type of neoplastic transformation that occurs in craniopharyngioma. However, in the clinical situation these histological distinctions are not always clear; a mixed form may exist. Therefore, it is recommended that symptomatic intra or suprasellar cystic lesions be surgically explored, to ensure correct diagnosis and appropriate treatment.