Pancreatic development is a complex process involving fusion of dorsal and ventral primordia; subtle deviations in this process frequently give rise to congenital anomalies of the pancreas.
Very rarely, the pancreas may be totally absent, a condition usually associated with additional severe malformations that are incompatible with life. IPF1 is a homeodomain transcription factor critical for normal pancreas development, and IPF1 gene mutations on chromosome 13q12.1 have been associated with pancreatic agenesis.
Pancreas divisum is the most common clinically significant congenital pancreatic anomaly, with an incidence of 3% to 10%. It occurs when the fetal duct systems of the pancreatic primordia fail to fuse. The main pancreatic duct (Wirsung) is very short and drains only a small portion of the head of the gland, while the bulk of the pancreas (from the dorsal pancreatic primordium) drains through the minor sphincter.
Annular pancreas is a relatively uncommon variant on pancreatic fusion; the outcome is a ring of pancreatic tissue that completely encircles the duodenum. It can present 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 are typically small (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 can cause pain from localized inflammation, or-rarely-can cause mucosal bleeding.
Congenital cysts probably result from anomalous ductal development. In polycystic disease, kidney, liver, and pancreas can all contain cysts. Pancreatic cysts range from microscopic to 5 cm in diameter. They are lined by duct-type cuboidal epithelium or can lack a cell lining altogether, and are enclosed in a thin, fibrous capsule.