Pancreatic development is a complex process involving fusion of dorsal and ventral primordia; subtle deviations in this process frequently give rise to congenital variations in pancreatic anatomy. While most of these do not cause clinical disease, variants (especially in ductal anatomy) can present challenges to the endoscopist and the surgeon. For example, failure to recognize idiosyncratic anatomy could result in inadvertent severing of a pancreatic duct during surgery, resulting in pancreatitis.
Very rarely, the pancreas may be totally absent, a condition usually (but not invariably) associated with additional severe malformations that are incompatible with life. Pancreatic duodenal homeobox 1 (PDX1) is a homeodomain transcription factor critical for normal pancreatic development, and germline mutations of this gene have been associated with pancreatic agenesis.
Pancreas divisum is the most common congenital anomaly of the pancreas, with an incidence of 3% to 10%. In most individuals, the main pancreatic duct (the duct of Wirsung) joins the common bile duct just proximal to the papilla of Vater, and the accessory pancreatic duct (the duct of Santorini) drains into the duodenum through a separate minor papilla. Pancreas divisum is caused by a failure of fusion of the fetal duct systems of the dorsal and ventral pancreatic primordia. As a result, the bulk of the pancreas (formed by the dorsal pancreatic primordium) drains into the duodenum through the small-caliber minor papilla. The duct of Wirsung in individuals with divisum drains only a small portion of the head of the gland through the papilla of Vater. More than 95% of individuals are asymptomatic. The remaining 5% develop acute or chronic pancreatitis, possibly related to inadequate drainage of pancreatic secretions through the minor papilla.
Annular pancreas is a relatively uncommon variant of pancreatic fusion in which a ring of pancreatic tissue completely encircles the duodenum. It can manifest with signs and symptoms of duodenal obstruction such as gastric distention and vomiting.
Aberrantly situated, or ectopic, pancreatic tissue occurs in about 2% of the population; favored sites are the stomach and duodenum, followed by the jejunum, Meckel diverticulum, and ileum. These embryologic rests typically are small (ranging from millimeters to centimeters in diameter) and are located in the submucosa; they are composed of normal pancreatic acini with occasional islets. Though usually incidental and asymptomatic, ectopic pancreas may become inflamed, leading to pain, or—rarely—can cause mucosal bleeding. Approximately 2% of pancreatic neuroendocrine tumors (Chapter 20) arise in ectopic pancreatic tissue.
Congenital cysts result from anomalous development of the pancreatic ducts. In polycystic disease, the kidneys, liver, and pancreas may all contain cysts (Chapter 14). Congenital cysts generally are unilocular and range from microscopic to 5 cm in diameter. They are lined by either uniform cuboidal or flattened epithelium and are enclosed in a thin, fibrous capsule. These benign cysts contain clear serous fluid—an important point of distinction from pancreatic cystic neoplasms, which often are mucinous (discussed later).
Inflammatory disorders of the pancreas are divided into acute and chronic forms. In acute pancreatitis, function can return to normal if the underlying cause of inflammation is removed. By contrast, chronic pancreatitis causes irreversible destruction of exocrine pancreas.