Duodenum

Overview

The duodenum is the first segment of the small bowel, connecting the stomach to the jejunum. It is a C-shaped hollow visucus predominantly on the right side of the vertebral column.

Origin

Continuous with the pylorus of the stomach, right of midline in transpyloric plane (L1)

Segments & Course

Superior segment (D1)

• Course
  • Passes laterally to the right at level L1 for 5cm before turning sharply inferiorly into the superior duodenal flexure
  • Suspended by the hepatoduodenal ligament part of the lesser omentum
  • Intraperitoneal for the first 2 – 3cm
• Relations
  • Anterior: gallbladder and the quadrate lobe of liver
  • Posterior: portal vein, common bile duct, gastroduodenal artery, neck of pancreas
  • Superior: epiploic foramen, hepatoduodenal ligament
  • Inferior: head of the pancreas

Descending segment (D2)

• Course
  • Begins at the superior duodenal flexure and descends to lower border of L3, lateral to the head of pancreas
  • Ends as it curves around head of the pancreas, passing medially into the inferior duodenal flexure
  • Secondarily retroperitoneal
  • Contains a minor papilla (superior) and major papilla (ampulla of Vater) or hepatopancreatic ampulla (inferior) in its medial wall for drainage of main and accessory pancreatic ducts
• Relations
  • Anterior: transverse mesocolon
  • Posterior: hilum of right kidney, right renal artery and vein, right ureter, right adrenal gland
  • Superior: liver, gallbladder
  • Inferior: loops of jejunum
  • Laterally: ascending colon, hepatic flexure (inferiorly), right kidney
  • Medial: head of pancreas

Inferior segment (D3)

• Course
  • Passes horizontally to the left at level L3, crossing midline
  • Turns superiorly to become D4
• Relations
  • Anterior: root of the mesentery, superior mesenteric artery and vein
  • Posterior: right psoas major, ureterand gonadal vessels, aorta, inferior vena cava
  • Superior: the uncinate process of the pancreas, left renal vein

Ascending segment (D4)

• Course
  • Ascends to level L2, reaching the inferior border of the body of pancreas
  • Curves anteriorly and terminates at the duodenojejunal junction
  • Duodenaljejunal junction attaches ligament of Treitz – superior attachment to coeliac trunk and right crus of the diaphragm
  • Continues as jejunum
• Relations
  • Superior: Body of pancreas
  • Posterior: Left psoas major muscle, renal artery and vein
  • Anterior: Stomach, greater omentum
  • Medial: Superior mesenteric artery and vein

Blood supply

Proximal to Ampulla of Vater

• Embryological foregut
• Supplied by branches of the gastroduodenal artery – branch of the common hepatic artery from ceoliac trunk
  • Supraduodenal artery
  • Anterior and posterior superior pancreaticoduodenal artery

Distal to the Ampulla of Vater

• Embryological midgut
• Supplied by anterior and posterior inferior pancreaticoduodenal artery – branches of the superior mesenteric artery
• Also supplied by first jejunal branch of superior mesenteric artery

Venous drainage

The veins of the duodenum follow the major arteries and drain into the portal vein.

• Superior pancreaticoduodenal veins drain directly into portal vein
• Inferior pancreaticoduodenal veins first drain into superior mesenteric vein, which then empties into the portal vein

Nerve supply

• Parasympathetic: Anterior and posterior vagal trunks
• Sympathetic: Coeliac plexus, greater splanchnic nerve

Variants

• Anomalous pancreaticobiliary union
• Annular pancreas
• Duodenal diverticulum – most commonly D2 or D3
• Duodenal duplication – most commonly occurs at the medial wall of D2 or D3, appears as a cystic structure that does not communicate with the lumen