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Duodenum – Superior part (D1)

The superior part of the duodenum (D1) is the first portion of the duodenum, approximately 5 cm long, extending from the pyloric orifice of the stomach to the superior duodenal flexure. It courses upward, backward, and to the right at the level of L1 vertebra, where it transitions into the descending part (D2).

The first 2 cm of the superior duodenum is called the duodenal bulb (ampulla), which is smooth internally and a common site for duodenal ulcers due to exposure to gastric acid. The distal part of D1 is crossed anteriorly by the gastroduodenal artery, making posterior ulcers clinically significant due to risk of hemorrhage.

The superior duodenum lies intraperitoneally at its proximal bulb, but the distal portion becomes retroperitoneal. Relations include:

  • Anterior: liver and gallbladder

  • Posterior: bile duct, gastroduodenal artery, portal vein, and IVC

  • Superior: epiploic foramen and gallbladder neck

  • Inferior: pancreas head

Synonyms

  • First part of duodenum

  • Duodenal bulb

  • Duodenal ampulla

Function

  • Receives chyme from stomach and regulates its passage into distal duodenum

  • Neutralizes gastric acid with alkaline secretions

  • Facilitates mixing of chyme with bile and pancreatic secretions (via downstream segments)

  • Plays a role in early digestion and absorption

Nerve Supply

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

  • Sympathetic: Greater and lesser splanchnic nerves via celiac plexus

  • Intrinsic enteric innervation regulates motility and secretion

Arterial Supply

  • Supraduodenal artery (branch of gastroduodenal artery)

  • Superior pancreaticoduodenal artery (from gastroduodenal artery)

  • Anastomoses with inferior pancreaticoduodenal artery (from SMA)

Venous Drainage

  • Superior pancreaticoduodenal vein → portal vein via gastroduodenal vein

  • Communicates with SMA tributaries, contributing to porto-systemic connections

MRI Appearance

T1-weighted images:

  • Duodenal wall shows intermediate signal intensity, lumen variable depending on contents (air, fluid, or chyme)

T2-weighted images:

  • Fluid within lumen appears bright hyperintense

  • Wall is intermediate signal; edema or inflammation (ulcer, duodenitis) shows hyperintensity

STIR:

  • Suppresses fat, highlighting duodenal wall thickening, edema, or periduodenal inflammatory changes

  • Useful in detecting acute duodenitis or perforation complications

T1 Fat-Saturated (Pre-contrast):

  • Duodenal wall appears as intermediate signal, contrasted against suppressed fat planes

  • Helps in identifying subtle mural thickening

T1 Fat-Saturated Post-Contrast (Gadolinium):

  • Normal wall enhances uniformly and thinly

  • Pathologies show heterogeneous, irregular, or thickened enhancement (ulcers, tumors, Crohn’s disease)

MRI Non-Contrast 3D Imaging:

  • Allows 3D reconstruction of the duodenal bulb and its relation to vessels and biliary tract

  • Useful for pre-surgical planning and congenital anomalies

CT Appearance

CT Pre-Contrast:

  • Duodenum appears as a tubular soft tissue structure at L1, lumen may show air or fluid

  • Ulceration may appear as focal wall thickening or luminal deformity

CT Post-Contrast:

  • Normal D1 wall enhances thinly and smoothly

  • Pathologies:

    • Duodenal ulcers: focal outpouchings or wall thickening

    • Tumors: irregular wall enhancement or mass lesion

    • Inflammation: mural thickening, fat stranding, possible perforation signs

MRI images

Duodenum – Superior part (D1) ct coronal image MRI coronal anatomy image -img-00000-00000

CT images

Duodenum – Superior part (D1) ct axial image

CT images

Duodenum – Superior part (D1) ct coronal image 1

CT images

Duodenum – Superior part (D1) ct coronal image