Overview
Gross Anatomy
The pylorus of the stomach (at L1 level) leads to the duodenum, which has the following 4 parts:
The duodenojejunal (DJ) junction or flexure is an abrupt turn (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 are found around this junction.
Stomach and duodenum, coronal section. 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).
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 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 before it divides into the right gastro-omental (gastroepiploic) artery (RGEA) and the anterior superior pancreaticoduodenal artery (SPDA). 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.
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 first (superior) part, or duodenal bulb (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 of the liver and the gallbladder are in front, whereas the CBD, the portal vein (PV), and the gastroduodenal artery (GDA) are behind it.
- The second (descending) part (10 cm), which has an upper and a lower genu (flexure); the transverse mesocolon and 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 C
- 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
- The fourth (ascending) part (2.5 cm) continues as the jejunum
The duodenojejunal (DJ) junction or flexure is an abrupt turn (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 are found around this junction.
Stomach and duodenum, coronal section. 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).
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 hepatopancreatic 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.
Blood supply
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 before it divides into the right gastro-omental (gastroepiploic) artery (RGEA) and the anterior superior pancreaticoduodenal artery (SPDA). 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.
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.
Nerves
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.Lymphatic drainage
Lymphatics from the duodenum drain into pancreaticoduodenal, supra- and infrapyloric, superior mesenteric, and celiac lymph nodes (LNs).Microscopic Anatomy
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.
Pathophysiologic Variants
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)
- A Ladd’s band runs across the duodenum and obstructs it; patients present clinically with signs of duodenal obstruction
Other Considerations
The following considerations should also be taken into account:
- A deformed duodenal bulb (on barium swallow and on endoscopy) in chronic (healed) peptic (duodenal) ulcer can occur
- 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 to control the vessel from inside the duodenum
- Pyloroplasty involves an incision in the stomach (antrum) and the first part of the duodenum as well
- An inflamed gallbladder can be adherent to the first part of the duodenum
- 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 peritoneum on its right aspect; the inferior vena cava (IVC) and left renal vein are encountered posteriorly
- Periampullary cancers include those of the lower CBD, ampulla, pancreatic head, and duodenum (including the papilla) within 1-2 cm of the ampulla
- Pancreaticoduodenectomy is required for resection of the pancreatic head and periampullary cancers because of the shared blood supply between the head of the pancreas and the second part (C loop) of the duodenum
- The duodenum is at risk for intraoperative injury during right hemicolectomy and right nephrectomy.
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