Duodenum
The duodenum is the first part of the small intestine and is the continuation of the stomach.
On this page:
Gross anatomy
The duodenum is a 20-30 cm C-shaped hollow viscus predominantly on the right side of the vertebral column. It lies at the level of L1-3 and the convexity of the duodenum (called the duodenal sweep by radiologists) usually encompasses the head of the pancreas.
The duodenum begins at the duodenal bulb and ends at the ligament of Treitz, where it continues as the jejunum (this is often called the duodenojejunal (DJ) flexure). It is composed of four distinct parts and is neither wholly peritoneal nor retroperitoneal.
Segments
First part (D1)
The first (superior) part of the duodenum begins as a continuation of the duodenal end of the pylorus. It passes laterally to the right, superiorly and posteriorly, for approximately 5 cm, before making a sharp curve inferiorly into the superior duodenal flexure. It is intraperitoneal for the first 2-3 cm only. Relations 3:
- anteriorly: gallbladder, liver
- posteriorly: common bile duct, portal vein, gastroduodenal artery
- superiorly: epiploic foramen
- inferiorly: pancreatic head
Second part (D2)
The second (descending) part of the duodenum begins at the superior duodenal flexure. It passes inferiorly to the lower border of vertebral body L3, before making a sharp turn medially into the inferior duodenal flexure, the end of the descending part. Relations 3:
- anteriorly: transverse mesocolon
- posteriorly: right kidney, right ureter, right adrenal gland
- superiorly: liver, gallbladder (variable)
- inferiorly: loops of jejunum
- laterally: ascending colon, hepatic flexure, right kidney
- medially: pancreatic head
The pancreatic duct and common bile duct enter the descending duodenum through the major duodenal papilla (ampulla of Vater). This part of the duodenum also contains the minor duodenal papilla, the entrance for the accessory pancreatic duct. The junction between the embryological foregut and midgut lies just below the major duodenal papilla.
Third part (D3)
The third (inferior/horizontal) part of the duodenum begins at the inferior duodenal flexure and passes transversely to the left, crossing the vertebral column. Relations 3:
- anteriorly: small bowel mesentery root
- posteriorly: right psoas muscle, right ureter, gonadal vessels, aorta and IVC
- superiorly: pancreatic head
- inferiorly: loops of jejunum
Fourth part (D4)
The fourth (ascending) part passes superiorly, either anterior to, or to the left of, the aorta, until it reaches the inferior border of the body of the pancreas. Then, it curves anteriorly and terminates at the duodenojejunal flexure where it joins the jejunum. The duodenojejunal flexure is surrounded by a peritoneal fold containing muscle fibers: the ligament of Treitz. Relations 3:
- superiorly: stomach
- inferiorly: loops of jejunum
- posteriorly: left psoas muscle, aorta
Arterial supply 3
- duodenal cap (first 2.5 cm): right gastric artery, right gastroepiploic artery
- remaining D1 to mid-D2: superior pancreaticoduodenal artery (branch of gastroduodenal artery)
- mid-D2 to ligament of Treitz: inferior pancreaticoduodenal arteries (branch of SMA)
Venous drainage 3
- duodenal cap (first 2.5 cm): prepyloric vein (drains to portal vein)
- remaining duodenum: superior pancreaticoduodenal vein (drains to portal vein) and inferior pancreaticoduodenal vein (drains to superior mesenteric vein)
Lymphatic drainage
- pancreaticoduodenal nodes that drain:
- distally to superior mesenteric nodes
- proximally to celiac nodes 3
Innervation
- sympathetic nerve fibers via celiac plexus
- parasympathetic nerve fibers via anterior and posterior vagal trunks 2
Variant anatomy
- duodenal diverticulum: most commonly occurs in D2 or D3 4
- 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 4
History and etymology
Duodenum means "twelve" in Latin and the name derives from the belief that it measured twelve finger widths in length (duodenum digitorum) 4.
Related pathology
- duodenal ulcer
- duodenitis
- duodenal diverticulum
- duodenal atresia
- duodenal web
- duodenal stenosis / duodenal stricture
- duodenal hematoma
- duodenal varices
See also
Related Radiopaedia articles
Anatomy: Abdominopelvic
- skeleton of the abdomen and pelvis
- muscles of the abdomen and pelvis
- spaces of the abdomen and pelvis
- anterior abdominal wall
- posterior abdominal wall
- abdominal cavity
- pelvic cavity
- perineum
- abdominal and pelvic viscera
- gastrointestinal tract
- spleen
- hepatobiliary system
-
endocrine system
-
adrenal gland
- adrenal vessels
- chromaffin cells
- variants
- pancreas
- organs of Zuckerkandl
-
adrenal gland
-
urinary system
-
kidney
- renal pelvis
- renal sinus
- avascular plane of Brodel
-
variants
- number
- fusion
- location
- shape
- ureter
- urinary bladder
- urethra
- embryology
-
kidney
- male reproductive system
-
female reproductive system
- vulva
- vagina
- uterus
- adnexa
- Fallopian tubes
- ovaries
- broad ligament (mnemonic)
- variant anatomy
- embryology
- blood supply of the abdomen and pelvis
- arteries
-
abdominal aorta
- inferior phrenic artery
- celiac artery
- superior mesenteric artery
- middle suprarenal artery
- renal artery (variant anatomy)
- gonadal artery (ovarian artery | testicular artery)
- inferior mesenteric artery
- lumbar arteries
- median sacral artery
-
common iliac artery
- external iliac artery
-
internal iliac artery (mnemonic)
- anterior division
- posterior division (mnemonic)
- variant anatomy
-
abdominal aorta
- portal venous system
- veins
- anastomoses
- arterioarterial anastomoses
- portal-systemic venous collateral pathways
- watershed areas
- arteries
- lymphatics
- innervation of the abdomen and pelvis
- lumbar plexus
-
sacral plexus
- lumbosacral trunk
- sciatic nerve
- superior gluteal nerve
- inferior gluteal nerve
- nerve to piriformis
- perforating cutaneous nerve
- posterior femoral cutaneous nerve
- parasympathetic pelvic splanchnic nerves
- pudendal nerve
- nerve to quadratus femoris and inferior gemellus muscles
- nerve to internal obturator and superior gemellus muscles