Benign and Malignant Tumors of the Small Bowel
Benign and malignant tumors of the small bowel are uncommon but have been increasing in incidence and mortality. Small bowel tumors were diagnosed at laparotomy or autopsy in the past. The advanced imaging modalities such as capsule endoscopy, device-assisted enteroscopy, or cross-sectional images (CT or MR enterography) make easier and earlier diagnosis of small bowel tumors. Although many histologic types of tumors develop in the small bowel, they can be classified as epithelial (benign and malignant), mesenchymal, lymphoproliferative, or metastatic tumors. The frequency of benign and malignant tumors varies in the countries. The most common tumor of the small bowel is adenocarcinoma in the duodenum. Malignant lymphoma and gastrointestinal stromal tumors are thought to be the most common tumors in the jejunum and ileum. Endoscopic differential diagnosis usually starts with observation of the overlying epithelial layer. Neuroendocrine tumors and mesenchymal tumors including stromal tumors, hamartomas, lipomas, lymphangiomas, and inflammatory fibroid polyps are usually covered with normal epithelial layers. The consistency of the tumors can differentiate the histologic types of tumors. Stromal tumors, neuroendocrine tumors, and inflammatory fibroid polyps are usually firm, while most hamartomas, lipomas, and lymphangiomas are relatively soft. Yellowish adipose tissue in lipomas and clear fluid in lymphangiomas are often seen though the overlying mucosa. Stromal tumors and neuroendocrine tumors often present with surface ulcers. The surface of epithelial tumors such as adenoma and adenocarcinoma can be well discriminated from the surrounding normal mucosa. The surface epithelium of lymphomas and metastatic tumors may be normal or change when tumor cells infiltrate the mucosal layer.
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