Duodenum: surgical anatomy

1. Location

• C-shaped loop around the head of the pancreas
• L1 to L3 vertebral levels
• Pylorus → duodenojejunal (DJ) flexure, at the ligament of Treitz
• Length → 25–30 cm ("12 fingers' breadth")
• Widest, shortest, most fixed part of the small bowel
• Retroperitoneal, except the first 2.5 cm (duodenal bulb) and the end of the fourth part
• Embryology → foregut above the major papilla, midgut below

2. Course and relations

First part (superior)

• Anterior → liver (quadrate lobe) and gallbladder
• Posterior → gastroduodenal artery (GDA), common bile duct (CBD), portal vein, inferior vena cava (IVC)
• Superior → epiploic foramen; first part forms its inferior boundary
• Inferior → head and neck of the pancreas
• Proximal half → intraperitoneal, mobile, attached to the hepatoduodenal ligament

Second part (descending)

• Anterior → transverse colon and root of the transverse mesocolon, right lobe of the liver, small bowel
• Posterior → right kidney, right renal vessels, IVC, right psoas major
• Medial → head of the pancreas, CBD
• Major duodenal papilla → posteromedial wall, about 10 cm from the pylorus
  • Range → 1.5–12 cm from the pylorus
  • Endoscopy → where a longitudinal fold meets a transverse fold in a "T"
• Minor duodenal papilla → 2 cm proximal to the major papilla; accessory pancreatic duct (of Santorini)

Third part (horizontal)

• Anterior → superior mesenteric artery (SMA) and vein (SMV), root of the small bowel mesentery
• Posterior → right ureter, right psoas major, right gonadal vessels, IVC, aorta
• Superior → head and uncinate process of the pancreas
• Inferior → jejunal loops
• Covers the origin of the inferior mesenteric artery in most cases

Fourth part (ascending)

• Runs up left of the aorta to the upper border of L2
• Anterior → transverse colon and mesocolon, lesser sac, stomach
• Posterior → left sympathetic trunk, left psoas major, left renal and gonadal vessels, inferior mesenteric vein (IMV)
• Paraduodenal fossae → peritoneal folds over the fourth part

Suspensory ligament of Treitz

• Fibromuscular band → from the right crus of the diaphragm to the DJ flexure
• Passes posterior to the pancreas and splenic vein, anterior to the left renal vein
• Insertion → flexure and 3rd–4th parts (most common), flexure only, 3rd–4th parts only, or multiple attachments
• Upper part skeletal muscle, lower part smooth muscle

3. Branches / Parts

1. First (superior) → 5 cm, L1
2. Second (descending) → 7.5 cm, L1–L3
3. Third (horizontal) → 10 cm, L3
4. Fourth (ascending) → 2.5 cm, L3–L2

Internal features

• Duodenal bulb → few longitudinal folds; triangular on contrast imaging
• Rest of the duodenum → circular folds (plicae circulares)
• Pyloroduodenal junction → abrupt thinning of the circular muscle (duodenal fornix around the os pylori)
• Brunner's glands → submucosal glands that mark the start of the duodenum

4. Blood supply, venous and lymphatic drainage

• Above the papilla → superior pancreaticoduodenal arteries from the GDA
• Below the papilla → inferior pancreaticoduodenal arteries from the SMA
• Veins → follow the arcades → SMV and portal vein
• Lymph → anterior and posterior pancreaticoduodenal nodes

5. Clinical significance

• Duodenal ulcer → 90% in the first part
• Posterior duodenal ulcer → erodes the GDA → major upper gastrointestinal haemorrhage
• First part → limited blood supply; skeletonising > 2 cm → stump blow-out or anastomotic failure
• Papilla position varies → pylorus is an unreliable landmark, worse with inflammation
• Kocher manoeuvre → mobilises the first, second and proximal third parts
• Superior mesenteric artery syndrome (Wilkie syndrome):
  • Normal aortomesenteric angle → 38–65°
  • Angle < 25° → third part compressed → obstruction
  • Treatment → duodenojejunostomy bypass (preferred) or division of the ligament of Treitz (Strong procedure)
• IMV → left of the paraduodenal fossae; at risk when incising peritoneum at the DJ flexure