What are causes of small bowel wall thickening (> 3 mm) on MDCT?
- Smooth and concentric bowel wall thickening is typical for nonmalignant disease (e.g., Crohn’s; ulcerative colitis; and ischemic, infectious, or radiation enteritis).
- Extraintestinal findings are important. In acute Crohn’s, MDCT is the best initial examination to evaluate for associated abscesses, fibrofatty proliferation, fistulas, mesenteric inflammation, and engorged vasa recta (“comb sign”).
- However, small bowel follow-through remains more sensitive for subtle mucosal changes and should be performed if suspicion for Crohn’s remains after a normal MDCT.
- MRI is excellent at diagnosing perianal disease, including fistulas.
- Eccentric and irregular bowel wall thickening of more than 2 cm, especially if confined to a short segment, is suspicious for malignancy.
- Carcinoid is the most common primary malignant small bowel tumor. Carcinoid is typically located in the ileum; however, the actual tumor is often small and not visible on CT.
- A surrounding desmoplastic reaction with spiculated, often calcified mesenteric lymph nodes suggests the diagnosis. Adenocarcinoma is the most common primary malignant proximal small bowel tumor. It often presents as a mass or annular stricture that may obstruct.
- B-cell lymphoma occurs in the distal small bowel (⅔) and T-cell lymphoma in the proximal small bowel (⅓). Massive mesenteric or retroperitoneal adenopathy is often present.
- Lipomas are easily recognized by their low attenuation (≈ –100 HU). The most common metastatic tumors to the small bowel include lung and melanoma.
