ABERRANT CRANIOPHARYNGEAL STRUCTURES WITHIN THE NEUROHYPOPHYSIS OF RATS

Aberrant craniopharyngeal structures within the neurohypophysis were a nalyzed in 17 rats, originating from four different colonies of Spragu e-Dawley- and Wistar-derived strains, which were used for toxicity stu dies in five different laboratories. Males were more frequently affect ed than females. The incidence of these findings, which occurred spont aneously and mainly in aged rats, was very low. Predominant features i ncluded tubular or acinar glandular structures, rarely embedded in a f ibrous stroma, and, as a rule, not compressing adjacent tissue. In som e cases, large cysts filled with colloid-like, amorphous material and cellular debris were present. The tubular structures consisted of a ra ther flat epithelium, while the cystic elements were lined by a cuboid al or columnar, rarely ciliated epithelium, containing goblet cells, o r by a stratified squamous epithelium. These structures reacted positi vely for cytokeratin. Acinar structures mimicked salivary glands of th e serous or mucinous type. In a few cases, small, round or fusiform ce lls were present. Distribution and predominance of the various epithel ial structures depended on the strain and colony of rats. Considering the ontogenic development of the pituitary gland, the morphological as pect of these lesions, their immunoreactivity and former reports on si milar findings, we concluded that these rats have aberrant craniophary ngeal structures within the pars nervosa of the hypophysis, originatin g from remnants of the ore-pharyngeal epithelium of the craniopharynge al duct (RATHKE's pouch). These lesions, which occurred in different s trains and colonies of laboratory rats, represent heterotopias or chor istomas, consisting of non-neoplastic growth disturbances. Being of a distinctly non-proliferative nature, they should not be confused with craniopharyngiomas.