An islet of Langerhans located within the epithelium of a human pancreatic duct.

An unusual structure resembling an islet of Langerhans was described in the pancreatic ductal epithelium of a presumably normal human male. Further studies to establish the identities of both islet and duct were performed. The original hematoxylin and eosin section served for histological description, as well as for nuclear volume analysis to characterize levels of beta cell polyploidy. The section was restained with Gomori's Chrome Alum Hematoxylin Phloxine to ascertain the presence of islet-like cells and to quantitate the ratio of beta- to non-beta cells. The section was then restained by the Feulgen technique to confirm proportionality between nuclear volume and DNA content. An apparently normal islet in the same section served as control. The combined observations were consistent with the interpretation that the structure is indeed an islet situated within the ductal epithelium. The almost complete absence of polyploid beta cells, however, and the high ratio of non-beta cells:beta cells suggested that it was a young islet. A similarly high proportion of non-beta cells in the control islet, as well as the frequent occurrence of ducts within, or in close proximity to, other islets, suggested that the entire islet organ was under some form of proliferative stimulus at time of resection. Alterations of the ductal epithelium and the secretory contents suggested that the duct was also in the process of transformation. Although the islet had apparently arisen within the ductal epithelium, the ultimate source of the progenitor cells could not be determined from these studies. The relationship of the ductal islet to other well known forms of islet regeneration is discussed.