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Jejunum

The jejunum is the second portion of the small intestine, situated between the duodenum proximally and the ileum distally. It constitutes approximately the proximal two-fifths of the intraperitoneal small intestine beyond the duodenojejunal flexure.

Anatomically, the jejunum is suspended by the mesentery of the small intestine, which contains blood vessels, lymphatics, and nerves. Compared to the ileum, the jejunum has a thicker wall, larger diameter, fewer mesenteric fat deposits, and more prominent circular folds (plicae circulares). Histologically, it is specialized for absorption with tall villi and abundant enterocytes.

Clinically, the jejunum is important in nutrient absorption, malabsorption syndromes, ischemia, Crohn’s disease, tumors, and small bowel obstruction. In radiology, identifying the jejunum versus ileum is crucial for accurate localization of pathology.

Synonyms

  • Middle small intestine

  • Mesenteric jejunum

  • Intestinum jejunum

Function

  • Primary site of nutrient absorption (carbohydrates, proteins, vitamins, and most minerals)

  • Facilitates digestion via secretions and motility

  • Contributes to immune defense with gut-associated lymphoid tissue (GALT)

  • Maintains fluid and electrolyte balance in coordination with ileum

Nerve Supply

  • Sympathetic: Lesser splanchnic nerves via the superior mesenteric plexus (reduces motility and secretion)

  • Parasympathetic: Vagus nerve (increases motility and secretion)

  • Sensory innervation through visceral afferents

Arterial Supply

  • Jejunal branches of the superior mesenteric artery (SMA) form arcades and straight vessels (vasa recta) within the mesentery

Venous Drainage

  • Jejunal veins drain into the superior mesenteric vein (SMV) → portal vein → liver

MRI Appearance

T1-weighted images:

  • Jejunal wall appears as intermediate signal intensity

  • Lumen varies depending on content (fluid: low signal, chyme: variable)

T2-weighted images:

  • Fluid-filled lumen appears bright hyperintense

  • Wall appears intermediate to low signal; mural edema appears hyperintense

STIR:

  • Suppresses fat, making the bowel wall and perienteric pathology more conspicuous

  • Useful for detecting edema, inflammation, or ischemia

T1 Fat-Saturated (Pre-contrast):

  • Jejunal wall appears intermediate signal, distinct from suppressed mesenteric fat

  • Vessels within mesentery stand out against fat suppression

T1 Fat-Saturated Post-Contrast (Gadolinium):

  • Jejunal wall shows homogeneous enhancement

  • Hyperenhancement or stratified enhancement indicates inflammation (enteritis, Crohn’s disease) or ischemia

  • Non-enhancing segments suggest necrosis

MRI Non-Contrast 3D Imaging:

  • Provides 3D reconstructions of jejunal loops, wall thickness, and vascular supply

  • Useful in MR enterography for Crohn’s disease, tumors, or obstruction

CT Appearance

CT Pre-Contrast:

  • Jejunum appears as a soft-tissue tubular loop with thicker folds (plicae circulares) than ileum

  • Useful for detecting obstruction, calcifications, or mural hemorrhage

CT Post-Contrast (Portal Venous Phase):

  • Jejunal wall enhances homogeneously in normal state

  • Stratified or target enhancement indicates inflammation or ischemia

  • Distension with oral contrast highlights folds for CT enterography

CT Enterography (CTV for small bowel):

  • Provides detailed view of jejunal wall, folds, and vasculature with neutral oral contrast

  • Gold standard for assessing Crohn’s disease, neoplasms, ischemia, and bleeding sources

  • 3D reconstructions demonstrate relation to mesenteric vessels and arcades

CT images

Jejunum ct coronal anatomy image -img-00000-00000

CT images

Jejunum CT axial image

CT images

Jejunum CT coronal image

MRI image

Jejunum MRI coronal anatomy image -img-00000-00000