Bowel wall thickening

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,aetiology but includes submucosal oedema, hemorrhagehaemorrhage, and neoplastic infiltration.

Radiographic features

In describing bowel wall thickening, certain descriptors can be useful in generating a differential diagnosis ¹

• how thick is the bowel wall?
  • mild, moderate, severe (subjective assessment)
• what is the attenuation / enhancement pattern of the bowel wall?
• how much of the bowel is affected?
  • short segment? multiple loops? small bowel and colon?
  • continuous involvement or discontinuous, ?skipare there any skip lesions?
• is the bowel wall thickened symmetrically or asymmetrically?

Plain radiography

• 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 / CT enterography

• some sources suggest >2-3 mm as a numerical cut off for small bowel wall thickening ²
• CT enterography is more useful for evaluation of bowel thickening because of
  • better luminal distention
  • earlier contrast timing that accentuates bowel wall mucosal enhancement

MRI / MR enterography

• findings in MRI and MR enterography are mostly analogous to CT, but submucosal oedema can be more directly evaluated with T2-weighted imaging

Differential diagnosis

• collapsed bowel

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

• inflammatory bowel disease, such as Crohn disease or ulcerative colitis
• diverticulitis
• infection, such as Clostridium difficile / pseudomembranous colitis
• bowel ischemia
• 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 hemorrhagehaemorrhage
• Henoch-Schonlein purpura
• oedema from hypoproteinemia

Practical points

• it can sometimes be difficult to differentiate between collapsed bowel and pathologic bowel wall thickening -- look for secondary signs such as mesenteric oedema, vascular engorgement, lymphadenopathy, or differential bowel wall enhancement to help confirm that the bowel wall thickening is pathologic
• if trying to decide if bowel wall is thickened or just collapsed, compare the wall with other loops of bowel in nearby and distant segments