Cyst formation of the craniopharyngeal duct.

The craniopharyngeal duct is the route by which the adenohypophysis ascends from the pharynx to the pituitary fossa. Rathke's cleft cyst represents an expansion of primitive vesicles that lie between the pars intermedia and the pars anterior. These cysts are rare but have been detected more frequently with the more widespread use of CT and MRI. Three cases are described which illustrate the variety of positions that a cystic lesion of the craniopharyngeal duct can occupy. These cases provide a basis for the discussion of the embryological formation of the pituitary, cyst formation of the duct, and CT and MRI appearances of the cysts.