terminal ileum

The terminal ileum is the most distal segment of small bowel. It immediately precedes the small bowel's connection with the colon through the ileocecal valve. It is of particular interest since a number of infectious and inflammatory processes preferentially involve the segment.

• location: the most distal ileum, ~30 cm proximal to the ileocecal valve
• blood supply: branches of the ileocolic artery, including the ileal branch of ileocolic artery and the recurrent ileal artery

Gross anatomy

Relations and/or Boundaries

Although the terminal ileum is more or less considered the 30 cm of ileum that precedes the ileocecal valve and cecum, it can also be thought of as a functional definition; the portion of distal ileum that is more lymphatic-rich than the rest of the ileum.

Arterial supply

The terminal ileum is supplied mainly by branches of the ileocolic artery (which arises off the superior mesenteric artery)

• ileal branch of ileocolic artery
• recurrent ileal artery

Venous drainage

• accompany the respective arteries and drain into the superior mesenteric vein

Lymphatic drainage

• lymphatic aggregates are more dense in this segment than elsewhere in the ileum

Radiographic features

Except in cases of intestinal malrotation, the terminal ileum is located in the right lower quadrant on imaging.

Fluoroscopy

Small bowel follow through (SBFT)

• circular folds are sparse in the terminal ileum and the mucosa can sometimes appear essentially featureless

Ultrasound

• normal ultrasound gut signature
• the terminal ileum can occasionally be mistaken for the appendix, but the terminal ileum is not blind-ending and usually is peristalsing

CT and MR enterography

• located in the right lower quadrant
• appears similar to other ileal loops unless inflamed
  • circular folds are more sparse in this segment than in other segments of the ileum

Related pathology

In addition to more general disorders involving the small bowel, the lymphatic-rich terminal ileum is a common target of some infectious organism and some generalized inflammatory processes

• terminal ileitis (differential)

In addition, because of its location immediately preceding the colon, it can be involved with colonic processes as well

• ileocolic intussusception
• backwash ileitis

False-positive evaluation for inflammatory bowel disease in the terminal ileum on fluoroscopy may be due to underdistention or nodular lymphoid hyperplasia.