Report of a rare cyst at a rare site: Heterotopic gastrointestinal cyst partially lined with dermoid cyst epithelium.

Heterotopic gastrointestinal cysts (HGCs) of the oral cavity are rare benign lesions mimicking benign or malignant pathologies. These cysts are usually discovered during infancy but may not appear until well into adulthood. The epithelial lining of these cysts shows variable presentation with the presence of an enteric lining as an essential component. The histogenesis is related to entrapment of undifferentiated, noncommitted endoderm within the oral cavity during the 3(rd) - 4(th) week of fetal life. We report a rare case of oral HGC located at a very rare site, i.e., infratemporal fossa with histopathologic features that included portions resembling dermoid cyst also. Histopathology and etiopathogenesis of the lesion are discussed. Origin from misplacement of embryonic remnants, i.e., undifferentiated endodermal cells is suggested.