Morphogenesis of craniopharyngeal derivatives in the neurohypophysis of fisher 344 rats: Abnormally developed epithelial tissues including parotid glands derived from the stomatodeum

Morphogenesis of craniopharyngeal derivatives of the neurohypophysis found in 14 Fischer 344 (F344) rats was studied. The incidence of the craniophary ngeal derivatives was 0.17% in male (7 out of 4,200) and 0.16% in female (7 out of 4,450) F344 rats. Neither a sex related difference in their inciden ce nor a strain-related difference in their morphological features was obse rved. Craniopharyngeal derivatives were composed of aberrant epithelial str uctures consisting of serous acinar and tubular and fusiform cell structure s, and most of these derivatives were associated with Rathke's cleft cysts, which are suggestive of a congenital background. The acinar structures wer e positive for periodic acid-Schiff reaction and negative for Alcian blue s tain. Immunohistochemically, cells forming these structures were positive f or cytokeratin, and basal cells of the acinar or tubular structures and som e of the fusiform cells showed positive staining for alpha-smooth muscle ac tin. Electron microscopically, these spindle-shaped basal cells had intracy toplasmic myofilaments with focal density in their cytoplasm, and they were regarded to be myoepithelial cells. These findings strongly indicate that the craniopharyngeal derivatives are not a neoplastic lesion but rather are a developmental aberration derived from the stomatodeum, which is known to be the origin of both nasal and oral epithelial tissues, including the par otid glands, other than Rathke's pouch.