Duodenal Anatomy

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The duodenum is the first part of the small intestine (5-7 m), followed by the jejunum and ileum (in that order); it is also the widest and shortest (25 cm) part of the small intestine. The duodenum is a C-shaped or horseshoe-shaped structure that lies in the upper abdomen near the midline (see the image below). ^{[1, 2]}

The pylorus of the stomach (at L1 level) leads to the duodenum, which has the following 4 parts:

The first (superior) part, or duodenal bulb or cap (5 cm), which is connected to the undersurface of the liver (porta hepatis) by the hepatoduodenal ligament (HDL), containing the proper hepatic artery, portal vein, and common bile duct (CBD); the quadrate lobe (segment IV) of the liver and the gallbladder are in front, whereas the CBD, the portal vein (PV), and the gastroduodenal artery (GDA) are behind the first part of the duodenum.

The second (descending) part (10 cm), which has an upper and a lower genu (flexure); the transverse mesocolon and transverse colon are in front, and the right kidney and inferior vena cava (IVC) are behind it; the head of the pancreas lies in the concavity of the duodenal C at the level of L2 vertebra

The third (horizontal) part (7.5 cm) runs from right to left in front of the IVC and aorta, with the superior mesenteric vessels (the vein on the right and the artery on the left) in front of it

The fourth (ascending) part (2.5 cm) continues as the jejunum

The duodenojejunal (DJ) junction or flexure is an abrupt turn at the level of L2 vertebra (see the image below); it is identified during surgery by the inferior mesenteric vein (IMV), which lies to its immediate left. The DJ junction is attached to the posterior abdominal wall by the suspensory muscle of the duodenum or the ligament of Treitz; many fossae (paraduodenal, duodenojejunal) are found around this junction.

Except for its first part, the duodenum is largely retroperitoneal and therefore fixed; it has no mesentery and is covered by peritoneum only on its anterior surface.

The first part of the duodenum divides the CBD into supraduodenal (in the HDL), retroduodenal, and infraduodenal (retropancreatic) parts; the terminal part of the CBD is intraduodenal (intramural) as it traverses the wall of the duodenum to open into its lumen (see Endoscopic anatomy).

The terminal part of the CBD is joined by the terminal part of the pancreatic duct in the pancreatic head to form a common channel (called the biliopancreatic ampulla when dilated), which runs through the medial duodenal wall and opens on the dome of the major duodenal papilla, a nipplelike projection on the medial wall of the middle segment of the second part (C loop) of the duodenum. The site of the greater duodenal papilla marks the junction of the embryologic foregut and midgut.

Both ampulla and papilla are eponymously related to Vater. The greater duodenal papilla is covered by a semicircular hoodlike mucosal fold superiorly. A smooth muscle sphincter (of Oddi) is present around the common channel of the CBD and the pancreatic duct and prevents reflux of duodenal juice into the 2 ducts.

The duodenal bulb (first part) is supplied by the right gastric artery and right gastro-epiploic artery.

The duodenum (C loop) shares its blood supply very intimately with the head of the pancreas, which lies in its concavity.

The celiac trunk (axis) arises as a branch from the anterior surface of the abdominal aorta at the level of T12–L1. It has a short length (about 1 cm) and trifurcates into the common hepatic artery (CHA), the splenic artery, and the left gastric artery (LGA). The CHA runs toward right on the superior border of the proximal body. The superior mesenteric artery (SMA) comes off as the second anterior branch from the abdominal aorta (the inferior mesenteric artery [IMA] is the third anterior branch) just below the origin of the celiac trunk at the level of L1 behind the neck of the pancreas and descends down in front of the third (horizontal) part of the duodenum to enter the small bowel mesentery.

The GDA, a branch of the CHA, runs down behind the first part of the duodenum in front of the neck of the pancreas and gives off the posterior superior pancreaticoduodenal artery (PSPDA) before it divides into the right gastroepiploic (gastroomental) artery (RGEA) and the anterior superior pancreaticoduodenal artery (ASPDA). The GDA also gives off the small supraduodenal artery (of Wilkie).

The inferior pancreaticoduodenal artery (IPDA) arises from the SMA and bifurcates into anterior and posterior branches. Anterior and posterior branches of the SPDA and IPDA join each other and form anterior and posterior pancreaticoduodenal arcades in the anterior and posterior pancreaticoduodenal grooves, supplying small branches to the first, second, and third parts of the duodenum (vasa recta duodeni) and to the head and uncinate process of the pancreas.

Veins accompany the SPDA and IPDA. Superior pancreaticoduodenal veins (SPDVs) drain into the PV, and inferior pancreaticoduodenal veins (IPDVs) drain into the SMV. ASPDV may drain into the gastro-colic trunk (GCT) of Henle.

The SMV lies to the right of the SMA in front of the third part of the duodenum. The union of the vertical SMV and the horizontal splenic vein (SV) forms the PV) behind the neck of the pancreas. The IMV lies to the immediate left of the DJ flexure and joins the junction of SV and SMV (or maybe SV or even SMV). The PV receives the SPDV, the right gastro-omental vein (RGEV), the left gastric vein (LGV), and the right gastric vein (RGV) and runs up (superiorly) behind the first part of the duodenum in the HDL) behind (posterior to) the CBD on the right and the proper hepatic artery (HA) on the left. The portal venous system (SV, SMV, and PV) has no valves.

The duodenum is supplied with parasympathetic nerves by hepatic and celiac branches of the anterior and posterior vagi, respectively, and with sympathetic nerves by branches of the celiac plexus.

Lymphatics from the duodenum drain into pancreaticoduodenal, supra- and infrapyloric, superior mesenteric, mesocolic and celiac lymph nodes (LNs).

The wall of the duodenum contains the same 4 layers that are seen in the remainder of the small bowel–namely, the mucosa (lined with columnar epithelium, containing lamina propria and muscularis mucosa), the submucosa, the muscularis propria (with inner circular and outer longitudinal layers), and the serosa (only on its anterior surface). The duodenal mucosa is characterized by the presence of Brunner’s glands, which secrete mucus. Endocrine cells in the duodenal wall produce cholecystokinin and secretin.

The following anomalies may be noted:

Duodenal atresia (stenosis) is associated with Down syndrome and manifests as neonatal gastric outlet obstruction; a radiograph of the abdomen reveals a double bubble (one in the fundus of the stomach and the other in the first part of the duodenum)

In malrotation of gut, the duodenojejunal flexure lies to the right (instead of normal left) of the spine. A Ladd’s band runs across the duodenum and obstructs it; patients present clinically with signs of duodenal obstruction

A perivaterian (around the ampulla/ papilla of vater) duodenal diverticulum may be present on the medial wall of the duodenum; it makes an endoscopic papillotomy difficult due to risk of its perforation. 

The following considerations should also be taken into account:

In blunt abdominal trauma, duodenal injuries are often associated with pancreatic injuries.

A deformed duodenal bulb (on barium swallow and on endoscopy) can occur in chronic (healed) peptic (duodenal) ulcer.

Peptic ulcer perforation occurs on the anterior wall of the first part of the duodenum.

Bleeding in the duodenal ulcer comes from the gastroduodenal artery (GDA), which runs vertically down behind the first part of the duodenum; a duodenotomy is performed on the anterior wall of the first part of the duodenum to control the vessel from inside the duodenum.

Pyloroplasty involves a longitudinal incision in the stomach (antrum) and the first part of the duodenum as well; the incision is then closed transversely.

An inflamed gallbladder can be adherent to the first part of the duodenum.

Gall bladder cancer can infiltrate the first part of the duodenum and cause gastric outlet obstruction (GOO).

Duodenal (gastric outlet) obstruction is present in most patients with pancreatic head cancer.

The first part of the duodenum is mobile and can be used for a biliary-enteric anastomosis (choledochoduodenostomy).

With a side-viewing (flexible) endoscope in the second part of the duodenum, the common bile duct (CBD) and the pancreatic duct can be cannulated through the papilla, and radiographs can be obtained after injection of radiologic contrast medium (endoscopic retrograde cholangiopancreatography [ERCP]).

Papilla may bleed after endoscopic papillotomy; control of bleeding involves duodenotomy (in the second part) and transduodenal sphincteroplasty.

Internal hernias can occur into the fossae around the duodenojejunal (DJ) flexure.

The Cattell Braasch maneuver is downward (inferior) mobilization of the hepatic flexure of the colon and the right transverse colon before mobilization of the duodenum.

Kocherization is anterior and leftward mobilization of the second part (C loop) of the duodenum after incision of the parietal peritoneum on its right aspect; the inferior vena cava (IVC) and left renal vein (LRV) are encountered posteriorly. Kocherization of the duodenum exposes the aortocaval area for an aortocaval lymph node biopsy.

Periampullary cancers include those of the lower CBD, ampulla, pancreatic head, and duodenum (including the papilla) within 1-2 cm of the ampulla.

Duodenal resection alone, without pancreatic resection, is technically difficult because of intimate sharing of blood supply.

Pancreaticoduodenectomy is required for resection of duodenal cancer because of the shared blood supply between the second part (C loop) of the duodenum and the head of the pancreas.

The duodenum is at risk for intraoperative injury during right hemicolectomy and right nephrectomy.

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Sinnatamby CS. Last’s Anatomy: Regional and Applied. 12th Ed. Edinburgh: Churchill Livingstone; 2011.

Susan Standring. Grays Anatomy. 41st. Elsevier; 2015.

Vinay Kumar Kapoor, MBBS, MS, FRCS, FAMS Professor of Surgical Gastroenterology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, India

Vinay Kumar Kapoor, MBBS, MS, FRCS, FAMS is a member of the following medical societies: Association of Surgeons of India, Indian Association of Surgical Gastroenterology, Indian Society of Gastroenterology, Medical Council of India, National Academy of Medical Sciences (India), Royal College of Surgeons of Edinburgh

Disclosure: Nothing to disclose.

Thomas R Gest, PhD Professor of Anatomy, Department of Medical Education, Texas Tech University Health Sciences Center, Paul L Foster School of Medicine

Disclosure: Nothing to disclose.

Duodenal Anatomy

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