Benign Pancreatic Disease

The pancreas begins as dorsal (from duodenum) and ventral (from hepatic diverticulum) budding from the foregut endoderm at approximately the fifth week of gestation.

Both the dorsal and ventral portions of the pancreas possess a main duct and fuse when the two pancreatic buds join. However, the portion of the dorsal duct between the anastomosis and the duodenum regresses. The main duct of the ventral pancreas leading to the duodenum is thus the definitive pancreatic duct (duct of Wirsung).

• a.

  If the two ducts do not fuse, the majority of the pancreas will drain via the dorsal bud duct ( duct of Santorini ), which is termed pancreas divisum.

• b.

  If the dorsal bud duct ( duct of Santorini ) fuses with the ventral bud duct ( duct of Wirsung ) but does not regress, then it will either persist as a blind accessory duct or drain via the lesser papilla.

Anomalies of pancreatic development include:

• a.

  Annular pancreas: a ring of pancreatic tissue that encircles the duodenum and rarely can cause duodenal obstruction

• b.

  Heterotopic pancreatic tissue: found most commonly in the duodenum, stomach mucosa, and in approximately 6% of Meckel diverticulum

Endocrine

• a.

  Islets of Langerhans—originate from embryonic ductal epithelium and migrate toward capillaries to form isolated islands of cells within the pancreatic exocrine tissue (acini)

  • (1)

    Alpha cells—cells within the islets that produce glucagon; first cells to develop (8–9 weeks)

  • (2)

    Beta cells—cells within the islets that produce insulin

  • (3)

    Delta cells—cells within the islets that produce somatostatin

  • (4)

    Gamma cells—cells within the islets that produce pancreatic polypeptide

Exocrine

• a.

  Acini—develops in three stages from pancreatic “founder” cells to become differentiated cells that store inactive digestive enzymes as zymogen granules

  • (1)

    Endopeptidases (trypsinogen, chymotrypsinogen, proelastase)

  • (2)

    Exopeptidases (procarboxypeptidase A and B)

  • (3)

    Others (amylase, lipase, phospholipase, colipase)

• b.

  Ductal—develops from the same pancreatic cellular cords as acinar cells. Originates from the centroacinar cells of each acinus and terminates into the main pancreatic excretory duct

Basics

• a.

  Retroperitoneal location posterior to the stomach at the level of L1–2 that is nested in the C-loop of the duodenum and lies obliquely to meet the splenic hilum.

• b.

  Access gained via separating the gastrocolic omentum from the transverse mesocolon to enter the lesser sac. The body and tail of the pancreas will be visible on the floor of the lesser sac.

Regions

• a.

  Head is positioned within the C-loop of the duodenum and posterior to the transverse colon. The head is anterior to the inferior vena cava, right renal artery, and bilateral renal veins.

• b.

  Uncinate process is the portion of the pancreatic head that projects to the right and posterior to the superior mesenteric vein. It terminates posterior to the superior mesenteric artery (SMA) and vein but anterior to the inferior vena cava and aorta. The tissue connecting the uncinate to the SMA is what is termed the retroperitoneal margin and is an important margin during pancreatectomy for pancreatic cancer.

• c.

  Neck divides the pancreas into near equal halves and is adjacent to the L1–2 vertebral bodies, making it susceptible to injury during blunt trauma. At the inferior edge of the neck, the splenic vein and superior mesenteric vein join to form the portal vein, which travels directly posterior to the neck of the pancreas on its way to the porta hepatis.

• d.

  Body lies directly anterior to the splenic artery and vein, with the artery running superior to the vein. Lies directly anterior to the aorta at the takeoff of the SMA, a good landmark to note on abdominal computed tomography (CT) scans.

• e.

  Tail extends to the left from the pancreatic body to lie near the splenic hilum anterior to the splenic artery and vein.

Arterial ( Fig. 30.1 )

• a.

  Celiac trunk

  • (1)

    The celiac trunk gives rise to the common hepatic artery, the left gastric artery, and the splenic artery. The hepatic artery gives off the gastroduodenal artery (GDA). The GDA divides into the anterior and posterior superior pancreaticoduodenal artery as it passes posterior to the first portion of the duodenum.

  • (2)

    The splenic artery supplies the body and tail of the pancreas as it courses along the superior posterior surface of the pancreas toward the spleen.

• b.

  SMA

  • (1)

    The SMA gives off the inferior pancreaticoduodenal artery. This divides into anterior and posterior branches and forms an anastomosis with the anterior and posterior branches of the superior pancreaticoduodenal artery within the pancreatic parenchyma. This anastomosis not only supplies the head of the pancreas but also the medial aspect of the duodenal C-loop. Therefore any resection of the pancreatic head involves resection of this portion of the duodenum; otherwise it will be devascularized.

  • (2)

    The dorsal pancreatic artery is a branch of the splenic artery that becomes the inferior pancreatic artery and travels parallel to the splenic artery but at the inferior border of the pancreas. Two main arteries run perpendicular to the pancreatic body and create an anastomosis between the splenic and inferior pancreatic arteries. They are the dorsal and greater pancreatic arteries (medial to lateral).

Venous

• a.

  Drainage follows similar routes as the arteries, but veins are more superficially located.

• b.

  The head of the pancreas is drained via veins located anterior and posterior to it.

  • (1)

    The anterior and posterior superior pancreaticoduodenal veins drain directly into the portal vein.

  • (2)

    The anterior inferior pancreaticoduodenal vein drains via the right gastroepiploic and right colic veins into the superior mesenteric vein.

  • (3)

    The posterior inferior pancreaticoduodenal vein drains into the inferior mesenteric vein.

• c.

  The body and tail of the pancreas drain into the splenic vein.

Lymphatics

• a.

  Diffuse drainage likely accounts for early and aggressive metastatic spread of tumor cells.

• b.

  Communication exists between pancreatic lymphatics and the transverse mesocolon and proximal jejunum mesentery.

Main pancreatic duct (duct of Wirsung) is approximately 2–3 mm in diameter.

It runs between the superior and inferior borders of the pancreas (one-third of the way up from the caudal margin), closer to the posterior aspect of the organ (two-thirds of the way in from the ventral surface).

The main pancreatic duct joins the common bile duct to empty into the second portion of the duodenum (medial aspect) at the ampulla of Vater (9% of the time the main duct and common bile duct [CBD] will be separate and will drain into the duodenum without the presence of an ampulla).

An accessory duct may be present approximately 2 cm proximal to the ampulla of Vater if the dorsal bud duct fails to regress during development (see Section I.A).