Atlas of Gastrointestinal Imaging, Chapter 4 -- The Mesenteric Small Bowel

Mesenchymal tumors are a heterogeneous group of intramural lesions that arise deep to the mucosa.

1.4 Mesenchymal Tumors

CLINICAL FEATURES

• Mesenchymal tumors are a heterogeneous group of intramural lesions that arise deep to the mucosa.

• Gastrointestinal stromal tumor (GIST) accounts for the majority of solid mesenchymal neoplasms; these tumors arise from the interstitial cells of Cajal (GI pacemaker cells).

• Other mesenchymal tumors include smooth muscle tumors (e.g., leiomyoma), neurogenic tumors (e.g., schwannoma, neurofibroma), vascular tumors (e.g., hemangioma), and hamartomas.

• GISTs were previously misclassified as smooth muscle tumors.

• Mesenchymal tumors may present with acute or occult GI bleeding secondary to ulceration of the overlying mucosa.

• Malignant mesenchymal tumors typically spread via direct local extension, intraperitoneal seeding, or hematogenously (to liver).

• Small bowel lipomas are generally benign incidental findings but may lead to intussusception.

• Hamartomas consist of varying amounts of smooth muscle and epithelial tissue.

• Multiple small bowel hamartomas are a common finding in Peutz-Jeghers syndrome; these benign polyps may act as lead points for intussusception.

• Hemangiomas and lymphangiomas of the small bowel are usually asymptomatic incidental findings; see section 3.9 for discussion of vascular ectasia.

• Most nerve sheath tumors (i.e., schwannomas and neurofibromas) are benign.

IMAGING FEATURES

• Mesenchymal tumors are intramural masses that typ­ically manifest as smooth, broad-based impressions on barium studies; nonulcerated lesions may be difficult to distinguish from extrinsic impression.

• CT and MR are useful for demonstrating both the intramural and exoenteric tumor components, which are typically much more prominent than the endolum­inal component.

• CT can evaluate for metastatic disease and monitor response to therapy (which is often striking in cases of GIST).

• A densely calcified lesion is suggestive of a leiomyoma.

• CT can provide an imaging-specific diagnosis for lipo­mas, obviating tissue sampling.

• Hemangiomas are typically small but can present as large polypoid lesions; the presence of phleboliths may allow for a specific diagnosis.

• Lymphangiomas may present as a polypoid or lobulat­ed submucosal lesion and may be pliable at fluoroscopy and endoscopy; most will appear cystic on cross-sectional imaging.

FIGURES

Figure 1.4.1 Small bowel GIST.

Figure 1.4.2 Ulcerated small bowel GIST.

Figure 1.4.3 Small bowel lipomas.

Figure 1.4.4 Small bowel hamartomas.

Figure 1.4.5 Peutz-Jeghers syndrome.

Copyright © 2007 by Saunders, an imprint of Elsevier, Inc.