MDCT of the Small Bowel

Grace A. Tye, MD; Terry S. Desser, MD


Appl Radiol. 2012;41(8):6-17. 

In This Article


Primary neoplasms of the small bowel, both benign and malignant, are rare. They are also difficult to diagnose, as direct visualization of most of the small bowel is not possible with conventional endoscopic procedures. Capsule endoscopy has been increasingly used, but its utility is controversial. Double-contrast enteroclysis has been considered the test of choice for evaluation of the small bowel, but its required technical expertise and invasiveness are drawbacks.[51] MDCT, particularly with the CT enterography protocol, has improved the ability ofCT to detect small-bowel tumors, and provides the added advantage of characterizing the extraluminal extension of disease.

A detailed description of the wide variety of small-bowel neoplasms is beyond the scope of this paper, but can be found in a number of previous publications.[51,52] Benign neoplasms include leiomyomas, gastrointestinal stromal tumors (GIST), lipomas, adenomas, and hemangiomas. A number of polyposis syndromes also affect the small bowel; they include familial adenomatous polyposis, Peutz-Jeghers syndrome, Gardner's syndrome, juvenile polyposis, Cronkihite-Canada syndrome, and Cowden's disease.

Malignant tumors account for up to 70% of small-bowel neoplasms. Adenocarcinomas are the most common of these, occurring most often in the duodenum, followed by the proximal jejunum. Risk factors for adenocarcinoma include celiac disease, Crohn's disease, and familial adenomatous polyposis. The CT appearance of adenocarcinoma can vary, but typically a focal segment of asymmetric bowel-wall thickening is seen, with moderate, heterogeneous enhancement and areas of mucosal ulceration. Extension through the serosa into the adjacent mesentery can be evaluated on CT, as well as the identification of metastases to lymph nodes and solid organs. Adenocarcinomas often narrow or occlude the bowel lumen and can cause obstruction, which can also be characterized on MDCT.

The second most common malignant neoplasm in the small bowel is the neuroendocrine, or carcinoid tumor, which originates from enterochromaffin cells. Fifty percent of neuroendocrine tumors are located in the appendix, with the second most common site being the ileum. Although they are hypervascular, these tumors are often small and difficult to identify on routine CT, although CT enterography may increase their conspicuity. Nodal metastases incite a desmoplastic reaction within the mesentery, resulting in a mass-like density with spiculated margins,calcifications, and marked tethering of adjacent bowel loops (Figure 1). This desmoplastic reaction is more easily detected on CT and can helpin establishing the diagnosis. Patients often present with fairly advanced disease, after the development of flushing, diarrhea, and intermittent hypertension. These symptoms of the "carcinoid syndrome" occur when liver metastases are present. Neuroendocrine metastases to the liver are hypervascular lesions that are best detected during the arterial phase of enhancement.

Lymphoma is the third most common malignant neoplasm of the small bowel and may arise from mucosa-associated lymphoid tissue (MALT). A systemic lymphoma can also affect the small bowel. Lymphoma has a variety of appearances on CT, ranging from a short segment of symmetric bowel wall thickening to a solitary mass infiltrating the surrounding mucosa to multifocal enhancing mucosal nodules.Secondary obstruction is uncommon, although intussusception can be seen. Lymphoma most often affects the ileum.

While most GISTs are benign tumors, they also have the potential for malignant transformation. No radiologic imaging findings other than metastatic disease can reliably differentiate benign from malignant disease, and thus, surgical resection of all GISTs is recommended. These mesenchymal tumors are more common in the stomach, but can occasionally be seen in the jejunum, where the typical appearance is that of an exophytic, bulky mass, often with areas of central cavitation and calcification. Metastases to the liver, in contrast to neuroendocrine metastases, are generally hypodense.

Metastatic disease affecting the small bowel can result from direct extension, intraperitoneal seeding, or hematogeneous spread. Malignancies that tend to directly invade the small bowel include pancreatic, biliary, or colonic neoplasms. Ovarian and colon adenocarcinomas can cause tumor implants along the serosal surface of the small bowel, and in their advanced stages, can result in obstruction.Common sources of hematogenously spread metastatic disease to the small bowel include lung, breast, and renal cell carcinomas, as well as melanoma (Figure 9).[51,52]


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