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
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.)
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.
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, 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. ...