Polypoid Lesions of the Small Bowel

Polypoid lesions of the small bowel can be mucosal or submucosal, which are differentiated by the angle they form with the small bowel wall. Mucosal lesions tend to form acute angles, while submucosal lesions form right or slightly obtuse angles. This distinction gets hard with small (< 2cm) lesions, however.

Almost 50% of submucosal lesions undergo necrosis and cavitation, giving us a submucosal "bull's-eye" or "target" appearance.

Muscosal lesions

• Polyps: May be pedunculated or sessile. Most commonly adenomas or hamartomas. When multiple, consider familial adenomatous polyposis syndrome (small bowel involved in 95% of patients) or Peutz-Jeghers syndrome (hamartomas). Coexistence of multiple duodenal polyps should steer you towards familial adenomatous polyposis syndrome, while a few large polyps in the distal duodenum and jejunum should steer you towards Peutz-Jeghers syndrome. Obviously if you could look at the patient and saw pigmented skin and mucosal lesions, you'd go with Peutz-Jeghers.
• Carcinoid: Can appear as mucosal lesions as one or more small sessile polyps in the distal ileum. By far the most common neoplasm in the distal small bowel.
• Adenocarcinomas: Usually in the duodenum, at or distal to the papilla of Vater, or in the proximal jejunum within 30 cm of the ligament of Treitz. Can ulcerate.

Submucosal Lesions

• Multiple submucosal masses: Think of hematogenous metastases (melanoma, breast or lung), lymphoma, multiple carcinoid tumors (will be mostly in the ileum), multiple neurofibromas (rarely ulcerate), and Kaposi sarcoma
• Solitary submucosal mass: Think benign lesions like lipoma, gastrointestinal stromal tumor, hemangioma, or neurofibroma.
• Pedunculated lesions: Large pedunculated lesions in the ileum are most commonly lipomas, inflammatory fibroid polyps, and inverted Meckel diverticula.

References

Levine MS, Rubesin SE, Laufer I. Pattern approach for diseases of mesenteric small bowel on barium studies. Radiology. 2008 Nov;249(2):445-60.