Topics

Topic

design image
Terminal ileum

The terminal ileum is the distal 30–40 cm segment of the small intestine, ending at the ileocecal junction, where it joins the cecum through the ileocecal valve. It is located in the right lower quadrant of the abdomen, suspended by the mesentery. Its mucosa contains Peyer’s patches (lymphoid aggregates), which play a critical role in immune surveillance of gut antigens.

The terminal ileum has specialized absorptive functions, most notably the absorption of vitamin B12 and bile salts, which are essential for red blood cell formation and fat digestion respectively. Because of its lymphoid tissue, it is also a common site for Crohn’s disease, lymphoma, and infections such as tuberculosis.

Anatomically, the terminal ileum lies close to the cecum, appendix, and ascending colon, which makes it a frequent surgical landmark in appendectomy, ileocecectomy, and right hemicolectomy.

Synonyms

  • Distal ileum

  • Ileal terminal segment

Function

  • Absorption of vitamin B12 and bile salts

  • Completion of nutrient absorption from small intestine

  • Contributes to gut immunity via Peyer’s patches

  • Acts as a valve-regulated conduit into the cecum

Nerve Supply

  • Sympathetic: Superior mesenteric plexus (via lesser splanchnic nerves, T10–T12)

  • Parasympathetic: Vagus nerve (via posterior vagal trunk)

Arterial Supply

  • Primarily from the ileocolic artery (branch of the superior mesenteric artery)

  • Additional contributions from terminal branches of SMA jejunoileal arteries

Venous Drainage

  • Ileocolic vein and tributaries drain into the superior mesenteric vein (SMV)

  • Ultimately contributes to the portal venous system

MRI Appearance

T1-weighted images:

  • Normal wall: intermediate signal intensity

  • Lumen: variable, depending on contents (fluid low signal, chyle intermediate signal)

T2-weighted images:

  • Lumen fluid: bright hyperintense

  • Normal wall: thin, hypointense rim

  • In Crohn’s or inflammation: thickened wall, hyperintense mucosa/submucosa with stratified appearance

STIR:

  • Suppresses fat, showing bright hyperintensity in inflamed bowel wall or mesenteric edema

  • Useful in detecting Crohn’s activity, abscesses, and phlegmon

T1 Fat-Saturated (Pre-contrast):

  • Wall: intermediate signal, highlighted against suppressed fat

  • Can delineate wall thickening better than conventional T1

T1 Fat-Saturated Post-Contrast (Gadolinium):

  • Normal ileum enhances thin and uniform

  • Inflammation: layered mural hyperenhancement (“target sign”)

  • Detects Crohn’s disease, ischemia, tumors, and ulceration

MRI Non-Contrast 3D Imaging:

  • Useful in MR enterography, showing full 3D configuration of ileum

  • Assesses strictures, fistulas, and pre-surgical mapping

CT Appearance

CT Pre-Contrast:

  • Terminal ileum appears as a tubular soft-tissue structure with thin walls

  • Lumen may contain fluid, air, or oral contrast in enterography studies

CT Post-Contrast:

  • Normal wall enhances thin and homogeneously

  • In Crohn’s disease: wall thickening, stratified enhancement, fat stranding, enlarged vasa recta (“comb sign”)

  • Detects strictures, perforation, fistulas, and tumors

CT images

terminal ileum CT axial anatomy image -img-00000-00000

MRI images

terminal ileum MRI sag anatomy image -img-00000-00000