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Development of the pancreas begins with the formation of 2 anlagen from the embryonic foregut. One arises from the dorsal aspect of the gut and the other from the ventral aspect. The dorsal anlage is initially located opposite to the hepatobiliary diverticulum. The ventral anlage arises from the duodenum at the caudal margin of the hepatobiliary diverticulum. The ventral anlage has right and left buds; the left bud normally regresses. There is progressive rotation of the ventral pancreas around the duodenum until it contacts and fuses with the dorsal segment. The common bile duct migrates with the ventral pancreas. The ventral pancreas forms the uncinate process and a portion of the head of the pancreas; the remainder of the pancreas derives from the dorsal anlage.
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The embryonic dorsal pancreas contains the duct of Santorini and the ventral pancreas contains the duct of Wirsung. As the dorsal and ventral components of the developing pancreas come into contact, the 2 pancreatic ducts fuse and the terminal segment of the embryonic dorsal (Santorini) duct atrophies. The dorsal duct loses its communication with the duodenum in most individuals and the remaining segment forms the accessory duct. Persistence of duodenal communication of this duct and failure of appropriate fusion of the dorsal and ventral ducts leads to the developmental anomaly of pancreas divisum. Anomalous communication between the common bile duct and the duct of Wirsung results in the common channel syndrome. Anomalous fusion of the dorsal pancreas and the ventral pancreas around the duodenum due to failure of degeneration of the left bud of the ventral pancreatic anlage causes annular pancreas.
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DEVELOPMENTAL ABNORMALITIES
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Annular pancreas is a rare developmental lesion in which a band of pancreatic tissue surrounds the second portion of the duodenum. This band is contiguous with the head of the pancreas and may be complete or incomplete. The major significance of this anomaly is the association with duodenal stenosis. Annular pancreas is, after pancreas divisum, the second most common congenital anomaly of the pancreas. This lesion is the most common symptomatic pancreatic anomaly. Annular pancreas occurs in 1 in 12,000 to 15,000 livebirths. Annular pancreas as a concomitant anomaly in 18% to 33% of children with duodenal atresia or stenosis.1,2
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The embryogenesis of annular pancreas involves abnormal duodenal development as well as abnormal pancreatic development. Vacuolation of the duodenum occurs between the 8th and 10th weeks of gestation. Deficiency in this vacuolation process likely accounts for congenital duodenal atresia or stenosis. These duodenal anomalies are sometimes associated with anomalous pancreatic tissue that surrounds and compresses the duodenum, that is, annular pancreas. Although the anomalous pancreatic tissue does compress the duodenum, intrinsic narrowing of the duodenal lumen is typically part of the pathophysiological process and is the major cause of obstructive symptoms. The etiology of annular ...