The pituitary in Turner syndrome.

Although Turner syndrome is not uncommon, studies of the pituitary in this condition are few. We undertook a histochemical and immunohistochemical study of four cases. As expected, "gonadal failure cells" were seen, but without recognizable gonadotroph hyperplasia. No gonadotroph adenomas were encountered. Instead, three silent corticotroph microadenomas were seen; their etiology remains unexplained. The question of whether the simultaneous occurrence of Turner syndrome and silent corticotroph adenoma is causal or incidental cannot be answered on the basis of the study of our material. Because these two diseases are rare, an etiologic association has to be considered. For example, it is possible that (a) protracted stimulation of gonadotrophs leads to transdifferentiation to corticotrophs, a hypothesis supported by the fact that normal and neoplastic gonadotrophs can contain ACTH and that some corticotroph adenomas produce LH and/or alpha subunit, (b) corticotrophs develop gonadotropin-releasing hormone (GnRH) receptors and undergo neoplastic transformation when exposed to continuous elevation of GnRH, FSH, and/or LH levels, and (c) the genetic defect in Turner syndrome promotes the formation of corticotroph adenomas.