Bowel wall thickening is a useful finding on imaging studies and has a number of different causes.

Pathology

The reason for bowel wall thickening depends on the underlying etiology but includes submucosal edema, hemorrhage, and neoplastic infiltration.

Radiographic features

In describing bowel wall thickening, certain descriptors should be considered when deriving a differential diagnosis ¹:

• bowel wall thickness

  • mild, moderate, severe (subjective assessment)

• bowel wall attenuation / enhancement pattern

• length of affected segment(s)

  • short segment or multiple loops

  • small bowel and/or colon

  • continuous involvement or discontinuous

    • skip lesions

• symmetrical or asymmetrical pattern

Plain radiograph

• bowel wall thickening can be seen through thickening of the valvulae conniventes (small bowel) or haustral folds (colon)

• the true thickness of the bowel wall should not be visible

  • if both sides of the bowel wall are visible, it likely indicates pneumoperitoneum

Fluoroscopy

• detection of bowel wall thickening on fluoroscopy is similar in principle to radiography and relies on evaluating the thickness of bowel wall folds

CT

• Some sources suggest >2-3 mm as a numerical cut off for small bowel wall thickening ² and >5 mm for large bowel wall thickening

• CT enterography is more useful for the evaluation of bowel thickening because of

  • better luminal distention

  • earlier contrast timing that accentuates bowel wall mucosal enhancement

MRI

Findings in MRI and MR enterography are mostly analogous to CT, but submucosal edema can be more directly evaluated with T2-weighted imaging.

Differential diagnosis

• collapsed bowel

If due to an inflammatory condition, the thickening represents submucosal edema. This type of thickening can be seen in 

• inflammatory bowel disease, such as Crohn disease or ulcerative colitis

• diverticulitis

• infection, such as Clostridioides difficile (pseudomembranous colitis)

• acute mesenteric ischemia

  • most prominent in venous ischemia ⁴

• radiation enteritis

Bowel wall thickening may also be due to neoplastic infiltration of the wall, such as with

• malignancy, such as colonic adenocarcinoma

• lymphoma

• graft vs. host disease

Bowel wall may be thickened in other conditions as well

• angioedema

• bowel trauma / submucosal hemorrhage

• Henoch-Schonlein purpura

• edema from hypoproteinemia

Practical points

• differentiation between collapsed bowel and pathologic bowel wall thickening may be difficult -- look for secondary signs such as mesenteric edema, vascular engorgement, lymphadenopathy, or differential bowel wall enhancement to help confirm that the bowel wall thickening is abnormal

• if trying to decide if the bowel wall is thickened or just collapsed, compare the wall with other loops of bowel in nearby and distant segments