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Duodenum – Descending part (D2)

The descending part of the duodenum (D2) is the second segment of the duodenum, approximately 7–10 cm long, extending from the superior duodenal flexure at the level of L1 vertebra down to the inferior duodenal flexure at L3. It lies to the right of the vertebral column, in close relation to the head of the pancreas, and is retroperitoneal.

The medial wall of D2 contains two major mucosal landmarks: the major duodenal papilla, where the common bile duct and main pancreatic duct empty (forming the hepatopancreatic ampulla of Vater), and the minor duodenal papilla, the opening of the accessory pancreatic duct.

Anatomically, D2 crosses in front of the hilum of the right kidney and is surrounded by the pancreas. This intimate relation explains the involvement of the descending duodenum in pancreatic head carcinoma, duodenal obstruction, and biliary disease.

Synonyms

  • Second part of duodenum

  • Descending duodenum

  • Pars descendens duodeni

Function

  • Receives and mixes chyme with bile and pancreatic secretions for digestion

  • Participates in enzymatic breakdown of food and absorption of nutrients

  • Coordinates gastrointestinal motility via neurohormonal regulation

Nerve Supply

  • Parasympathetic: Vagus nerve (via celiac and superior mesenteric plexuses)

  • Sympathetic: Greater and lesser splanchnic nerves via the celiac and superior mesenteric plexuses

Arterial Supply

  • Superior pancreaticoduodenal artery (from gastroduodenal artery, celiac trunk)

  • Inferior pancreaticoduodenal artery (from superior mesenteric artery)

  • Forms important anastomosis between celiac and SMA circulations

Venous Drainage

  • Superior pancreaticoduodenal vein → portal vein

  • Inferior pancreaticoduodenal vein → superior mesenteric vein

  • Provides porto-systemic venous linkage

MRI Appearance

T1-weighted images:

  • Duodenal wall shows intermediate signal intensity; lumen depends on contents (fluid = low, chyme = variable)

  • Pancreatic and bile duct insertions visible as small hypointense tubular structures

T2-weighted images:

  • Duodenal wall is intermediate to low signal; intraluminal fluid is bright hyperintense

  • Papillary region well defined if fluid-distended

STIR:

  • Suppresses fat, accentuating wall edema, inflammation, or peri-duodenal collections

  • Useful in duodenitis, pancreatitis, or trauma

T1 Fat-Saturated (Pre-contrast):

  • Duodenal wall shows intermediate signal against suppressed fat

  • Improves visualization of periduodenal margins

T1 Fat-Saturated Post-Contrast (Gadolinium):

  • Duodenal wall enhances uniformly when normal

  • Abnormalities: irregular thickening and heterogeneous enhancement in tumors, strong enhancement in duodenitis, variable enhancement in ulcers

MRI Non-Contrast 3D Imaging:

  • Provides 3D reconstruction of duodenum and adjacent pancreas

  • Used in MRCP (magnetic resonance cholangiopancreatography) to visualize the papilla and bile/pancreatic duct entry points

CT Appearance

CT Pre-Contrast:

  • Duodenal wall appears as a thin soft-tissue rim; lumen may contain air, fluid, or contrast

  • Calcifications may suggest chronic pancreatitis encroaching on D2

CT Post-Contrast:

  • Duodenal wall enhances homogeneously in normal state

  • Focal thickening, heterogeneous enhancement, or mass lesions suggest neoplasm or inflammation

  • Visualizes relations with pancreas, biliary tract, and vessels

MRI image

Duodenum – Descending part (D2) MRI coronal anatomy image -img-00000-00000

CT images

Duodenum – Descending part (D2) CT coronal image

CT images

Duodenum – Descending part (D2) CT axial image