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Duodenum – Ascending part (D4)

The ascending part of the duodenum (D4) is the short terminal segment of the duodenum, measuring about 2.5–3 cm in length. It begins at the duodenojejunal flexure, where the duodenum transitions into the jejunum, and lies to the left of the aorta and vertebral column at the level of L2.

The D4 segment is anchored by the suspensory ligament of the duodenum (ligament of Treitz), a fibromuscular band extending from the right crus of the diaphragm to the duodenojejunal flexure. This ligament maintains the sharp bend between the duodenum and jejunum, an important surgical and radiological landmark.

Posterior relations of D4 include the aorta and left psoas major muscle, while anteriorly it is related to the root of the mesentery. Its position and fixation make it significant in intestinal obstruction, malrotation, and vascular compression syndromes (e.g., superior mesenteric artery syndrome).

Synonyms

  • Fourth part of the duodenum

  • Duodenum ascendens

  • D4

Function

  • Transmits chyme from the duodenum to the jejunum

  • Serves as the transition point between duodenum (foregut/midgut) and jejunum (midgut)

  • Aids in neutralization of gastric acid and mixing of chyme with bile and pancreatic enzymes

  • Acts as a surgical landmark for procedures involving the duodenojejunal junction

Nerve Supply

  • Parasympathetic: Vagus nerve via celiac and superior mesenteric plexuses

  • Sympathetic: Lesser and least splanchnic nerves via the superior mesenteric plexus

Arterial Supply

  • Inferior pancreaticoduodenal artery (branch of superior mesenteric artery)

  • Anastomoses with branches of the superior pancreaticoduodenal artery (branch of gastroduodenal artery)

Venous Drainage

  • Inferior pancreaticoduodenal vein drains into the superior mesenteric vein

  • Contributes to the portal venous system

MRI Appearance

T1-weighted images:

  • D4 wall appears as intermediate signal intensity

  • Lumen variable depending on chyme or air content

T2-weighted images:

  • Lumen fluid shows bright hyperintense signal

  • Wall appears as low-to-intermediate signal; wall thickening seen in inflammation

STIR:

  • Fat suppression makes bowel wall pathology (edema, inflammation, tumor) more conspicuous

  • Highlights perienteric fat stranding in duodenitis or malignancy

T1 Fat-Saturated (Pre-contrast):

  • Wall demonstrates intermediate signal intensity, standing out against suppressed mesenteric fat

T1 Fat-Saturated Post-Contrast (Gadolinium):

  • Wall enhances uniformly when normal

  • Heterogeneous or irregular enhancement indicates duodenitis, ischemia, or neoplasm

MRI Non-Contrast 3D Imaging:

  • Provides detailed 3D visualization of duodenojejunal flexure, ligament of Treitz, and vascular relationships

  • Useful in congenital malrotation, obstruction, and surgical planning

CT Appearance

CT Pre-Contrast:

  • D4 appears as a tubular structure with soft-tissue wall density, lumen may contain air, fluid, or contrast residue

  • Wall thickening or calcifications may suggest pathology

CT Post-Contrast:

  • Normal wall enhances uniformly

  • Irregular or asymmetric enhancement suggests inflammation, ischemia, or malignancy

  • Multiplanar reconstructions delineate relationship to aorta, SMA, and mesenteric root

MRI image

Duodenum – Ascending part (D4) MRI coronal anatomy image -img-00000-00000

CT images

Duodenum – Ascending part (D4) CT axial anatomy image -img-00000-00000

CT images

Duodenum – Ascending part (D4) CT axiall anatomy image -img-00000-00000

CT images

Duodenum – Ascending part (D4) CT sag anatomy image -img-00000-00000

CT images

Duodenum – Ascending part (D4) ct coronal image