The origin of Rathke's cleft cysts lies in the embryological development of the pituitary gland. During development, a small diverticu-lum lined with endodermal epithelium -Rathke's pouch - grows from the roof of the primitive buccal cavity or stomatodeum. Simultaneously a small ectodermal process -the infundibulum - grows downwards from the floor of the diencephalon. During the second month of development Rathke's cleft lies in contact with the anterior surface of the infundibulum, and its connection with the oral cavity disappears. Rathke's pouch now flattens itself around the anterior and lateral surface of the infundibulum, forming the pars anterior, pars tuberalis (around the infundibulum) and pars intermedia. These embryological distinctions are rarely seen clinically. The cystic center of Rathke's cleft normally now disappears. It is the persistence and growth of this vesicular space, probably by epithelial proliferation and accumulation of secretions, that give rise to Rathke's cleft cysts. Other theories of RCC formation postulate origin from neuroepithelial tissues or from anterior pituitary cells by reverse metaplasia. The relatively common finding of squamous epithelium in portions of the cyst lining has led to the hypothesis of origin from squamous rests along the cranio-pharyngeal canal (or hypophyseal-pharyngeal duct). This is a theory that might explain a possible common origin of a spectrum of cystic sellar lesions ranging from RCCs to cranio-pharyngiomas.
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