Tumors of the small intestine

Last revised by Arlene Campos on 11 Jan 2024

The small intestine is rarely the site of malignant tumors, although it accounts for ~75% of the entire length of the GI tract and more than 90% of the mucosal surface. Approximately 40 different histologic tumor types have been described. 

In this article, an overview will be given of the most common benign and malignant types of small bowel tumors, including their imaging characteristics.

Primary neoplasms of the small intestine are very rare, comprising approximately ~4% (range 1.6-6%) of all tumors of the gastrointestinal tract 1,2.  Approximately 60% of these tumors are malignant. Benign neoplasms of the small intestine comprise ~5% of benign tumors of the intestinal tract. Most present in the 5th and 6th decades 1

The most frequent malignant tumors are 1,2:

The most frequent benign tumors are 1,2:

Metastases are more common in the small intestine than primary tumors and may occur by hematogenous spread, local extension or intraperitoneal seeding 1.

The clinical manifestations are non-specific and can include:

Tumor-related obstructions do not produce symptoms until a late stage, due to the fluid contents of the small intestine. Imaging at that time, usually, documents an advanced tumor stage with a correspondingly low 5-year survival rate (<20%).

Can involve the duodenum, proximal jejunum and distal ileum 1,2.  The duodenum is most at risk for adenocarcinomas and the ileum for carcinoid tumors and lymphomas 2.

Numerous pathogenetic mechanisms have been mentioned regarding the low susceptibility of the small bowel to malignant change. The most cited are 2:

  • rapid transit of intestinal contents (short exposure of the mucosa to carcinogens)

  • moderation of mucosal irritation by the liquid nature of the small bowel contents

  • low bacterial load

  • relatively high concentration of lymphoid tissue

Some inflammatory disorders predispose to malignancy 1,2:

Various genetic disorders are also associated with an increased incidence of small bowel tumors 1,2:

Gastric and colonic endoscopy, ultrasound and small bowel barium examinations are the first-line studies for all non-specific clinical GI symptoms.

Enterography (and enteroclysis) with CT and especially MRI have become important in the investigation of GI disorders. These techniques are superior to enteroclysis in the evaluation of eccentric tumors and secondary lesions (peritoneal carcinomatosis).

With MRI, the spatial resolution is less than that achieved with conventional enteroclysis or CT, therefore it is less useful for evaluation of lesions <5 mm.

Endoscopic ultrasonography (EUS) is very sensitive and effective for the workup of neoplasms in the ampullary region.

CT angiography may be useful for demonstrating the site of bleeding and the responsible lesion.

Capsule endoscopy has facilitated early diagnosis of small bowel tumors 2.

  • small bowel leiomyoma 1,2

    • 1-10 cm in size

    • mostly located in the jejunum

    • typically rounded, well-circumscribed

    • frequently ulcerate and cause bleeding

    • obstructive in case of intraluminal growth

    • irregular lesion margins and enlarged lymph nodes should raise suspicion of leiomyosarcoma

    • angiography: hypervascular lesion

    • MRI

      • intermediate signal on T1 and slightly increased on T2

      • moderate, homogeneous contrast enhancement

      • tumor necrosis and calcifications can be present

    • MRI is better than enteroclysis for showing extraluminal growth patterns

  • small bowel adenoma 1,2

    • 1-3 cm in size

    • predominantly in the duodenum, also in the ileum (ileocecal valve)

    • one-third occurs in the setting of Peutz-Jeghers syndrome

    • large polyps may cause intussusception

    • enteroclysis:

  • small bowel lipoma 1,2

    • mostly located in the ileum (ileocecal valve)

    • MRI: typically high signal on T1 and loss of signal with fat saturated images

    • no contrast enhancement with CT/MRI

  • small bowel hemangioma 1,2

    • predominantly in jejunum

    • may cause severe GI bleeding

    • cavernous types resemble a submucosal polyp

    • capillary types are multiple and may appear as small, flat, inconspicuous filling defects on enteroclysis

    • MRI

      • typically show high T2 signal and intense enhancement

      • smaller lesions can be missed on MRI, mesenteric angiography may be performed in cases with occult hemorrhage

  • small bowel carcinoid

    • 30-45% occurs in the appendix, 25-35% in the small intestine (90% in distal ileum)

    • characterized by increased serotonin production

    • typically invasive growth and pronounced perifocal fibrotic reaction (desmoplastic reaction)

    • features: muscularis propria thickening, puckering, wall retraction, serosal invasion, mesenteric metastases (similar echogenicity to the primary tumor, may calcify)

    • MRI

      • T1isointense to bowel wall

      • T2iso- to hypointense

      • extraluminal desmoplastic streaks (spoke-wheel pattern), mesenteric retraction and kinking of bowel loops

      • encasement of mesenteric blood vessels may lead to chronic ischemia

    • CTdystrophic calcifications can be seen (better with CT than MRI)

    • hypervascular carcinoids are typically demonstrated in the arterial phase

    • ultrasound: smooth, intraluminal, hypoechoic masses interrupting the submucosal layer 3

  • small bowel adenocarcinoma 1,2

    • most common GIT malignancy 3

    • mostly located near the papilla in the duodenum, less frequently in jejunum

    • enteroclysis: infiltrative tumor with irregular and segmental luminal narrowing

    • MRI: non-specific intermediate SI on T1 and T2

    • asymmetrical nodular wall thickening

    • non-homogeneous moderate contrast enhancement

    • streaky infiltration of the mesentery indicates tumor spread

    • regional mesenteric lymphadenopathy

    • US: similar to other bowel tumors, hypoechoic, loss of gut signature, obstruction 3

  • small bowel leiomyosarcoma 1,2

    • may occur anywhere in the small bowel, mainly ileum and jejunum

    • large tumors, usually >6 cm, with extraluminal growth

    • imaging findings are comparable to leiomyoma (see above), and the differentiation can be difficult

    • frequently ulcerate and cause bleeding

    • intraperitoneal hematogenous seeding is common

  • small bowel lymphoma 1

    • typically shows asymmetrical but circumferential wall thickening with associated luminal dilatation (intestinal aneurysm), due to tumor extension into muscularis propria and destruction of autonomic nerve plexus

    • rarely causes bowel obstruction (tumor does not elicit desmoplastic response)

    • significant enlargement of mesenteric lymph nodes

    • MRIlow on T1, slightly increased on T2, hypovascular and thus very little contrast enhancement

    • ultrasound: wide variety of appearances, anechoic/hypoechoic, destruction of gut signature, aneurysmal dilation, wall thickening 3

  • gastrointestinal stromal tumor (GIST) 3

    • most common mesenchymal tumor

    • from interstitial cells of Cajal which regulate gut peristalsis

    • most frequently affect the stomach and small bowel

    • intraluminal mass or can extend through serosa as an exophytic mass with a large extraluminal component 4

    • bowel obstruction is rare even with large tumors 4

    • tends to displace adjacent structures rather than direct invasion

    • 50% have metastases at time of diagnosis (liver, peritoneum)

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Cases and figures

  • Figure 1: macroscopic-small bowel hemangioma
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  • Case 1: leiomyosarcoma of small bowel
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  • Case 2: Gastrointestinal stromal tumor of small bowel in CECT
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  • Case 3: adenocarcinoma of the duodenum
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