4 Pancreas

Size

●Head: 2.5–3 cm

●Body: < 1.8–2 cm

●Tail: 2.5–3 cm

Shape

●Dumbbell

●Tadpole (pollywog)

The structure of the pancreas shows it to be a composite tubuloalveolar gland. Its size may vary significantly, depending on age and its intrinsic physiological variation in shape; in elderly people the organ becomes smaller and may even atrophy.

Embryonically the pancreas consists of a ventral and a dorsal primordium. Their two ducts, the pancreatic duct (Wirsung’s duct) and the accessory pancreatic duct (duct of Santorini), join together to form a common duct, the main pancreatic duct. The remaining pan-

creatic duct in the pancreatic head drains to the ampulla of Vater. During embryonic development, the accessory pancreatic duct shrinks and drains to the minor papilla. Incomplete fusion leads to pancreas divisum, and a persistent ventral anlage ventrally to the duodenum leads to an annular pancreas.

The variants in shape (dumbbell and tadpole, Fig. 4.1) are characterized by their differences in the size of the pancreatic head and tail. Most confrom to the dimensions given above.

Microstructure. The enzyme-producing terminal segments of the glands are termed acini (“berries”). The interstices house blood vessels, fibroblasts, and strands of collagen, and this interstitial connective tissue becomes denser with age. During embryological development the pancreatic duct becomes the main drainage. Accessory ducts, termed interlobular excretory ductules, branch off it orthogonally. Further branching to the acini within the lo-

Topographic relationships

●Retroperitoneal location anterior to the upper lumbar spine

●Head—anterior to the inferior vena cava

●Body—transverse in the middle of the upper abdomen anterior to the aorta

●Tail—reaches the hilum of the spleen

Ultrasound landmark structures

●Portal vein confluence and its tributaries

●Inferior vena cava

●Vessels of the celiac axis

The pancreas lies transversely and somewhat obliquely in the retroperitoneum, directly anterior to the spine at the level of the second lumbar vertebra. The head of the pancreas nes-

tles in the posterocaudad concavity of the duodenum; the pancreatic body traverses the spine and courses along the anterior margin of the left kidney, while the tail reaches cephalad into the hilum of the spleen (Figs. 4.2, 4.3, 4.4).

Borders. The posterior borders are defined by the spine and the lumbar part of the diaphragm, abdominal aorta, and inferior vena cava, all anterior to the spine. Most of the anterior aspect of the pancreas is covered by the stomach. The omental bursa is formed by the posterior wall of the stomach (up to the lesser curvature) and the anterior aspect of the pancreas. From the border between the head and body of the pancreas to the left, there is the cavity of the omental bursa or lesser sac, which in acute pancreatitis may fill up with exudate.