Immunohistochemical and gross dissection studies of annular pancreas.

Three cases of annular pancreas were studied immunohistochemically on an embryological basis in relation to the duct system. Annular pancreatic tissue was characterized by abundant, irregularly shaped islets with a very high proportion of pancreatic polypeptide (PP) cells, similar to those in the postero-inferior part of the pancreatic head of controls. This PP-rich area fused with PP-poor areas in both the anterior and posterior portions, resulting in encirclement of the duodenum except for a few PP-poor areas. The pancreatic duct of the annular tissue passed from the anterior portion to the lateral and posterior portions, finally joining with the main pancreatic duct. No connection was present between the duct of the anterior portion and the main pancreatic duct. Therefore, the annular pancreatic tissue was revealed to arise from the ventral primordium, supporting Lecco's theory that the free end of the ventral anlage is fixed.