Chapter 417

In the fourth week of gestation, the human pancreas develops as two outpouchings of the duodenal endoderm (Figure 381-3 and eFig. 417.1).1-3 The larger dorsal bud develops into the tail, body, and a portion of the head of the pancreas. The ventral bud fuses with the dorsal bud at about the 17th week of gestation to create the remainder of the head of the pancreas and the uncinate process. Each bud possesses its own ductal system; variations in fusion, which occurs in 15% of the population, lead to developmental anomalies. The dorsal duct forms the distal portion of the duct of Wirsung and the ventral portion forms the accessory duct of Santorini, which empties independently in about 15% of the population. Defective fusion of the two pancreatic primordia leads to a number of anatomic anomalies of the pancreatic ductal system (see also Chapter 381). Anomalies in this developmental process can have clinical implications.

###### eFigure 417.1.

Pancreatic organogenesis in mice. Yellow shading indicated the pancreatic region (epithelium and mesenchyme) within the developing endoderm. Formation of pancreatic bud begins at approximately E9. After extensive branching and growth, the pancreatic ductal epithelium differentiates into exocrine cells (green) and endocrine cells (blue and red), the latter of which migrate into the surrounding mesenchyme. In adult mice, 3 cell types are found: acinar, ductal, and endocrine.

(From Cano DA. Pancreatic development and disease. Gastroenterology 2007; 132:749.)

### Pancreas Divisum

Pancreatic divisum, which arises from incomplete fusion of the dorsal and ventral pancreatic ductal systems, occurs in 5% of the population.4,5 In pancreas divisum the major portion of the gland is drained by the minor duct of Santorini. When there is partial obstruction, recurrent pancreatitis may occur. Pancreatic divisum is diagnosed by endoscopic retrograde cholangiopancreatography (ERCP) or by magnetic resonance cholangiopancreatography (MRCP). Endotherapy is the treatment of choice.

### Common Pancreaticobiliary Junction

The presence of a common channel, with the pancreaticobiliary junction outside the duodenal wall, is associated with pancreatitis and implicated in the pathogenesis of choledochal cysts. The diagnosis can now be made noninvasively by magnetic resonance cholangiopancreatography.

### Annular Pancreas

Annular pancreas, which arises from incomplete rotation of the ventral bud, can produce symptoms at any age. Presentation in infancy usually is characterized by high obstruction following polyhydramnios in utero. A “double bubble” appearance on plain-film abdominal radiographs is typically seen (see Chapter 389). In older children, partial obstruction may give rise to recurrent vomiting. The treatment of choice is duodenojejunostomy. Division of the pancreatic ring is not attempted, because a duodenal diaphragm or duodenal stenosis frequently accompanies annular pancreas. Annular pancreas may be associated with Down syndrome, intestinal atresia, imperforate anus, pancreatitis, and malrotation. Genetic causes of annular pancreas and other pancreatic disorders are found in Table 417-1...

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