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Chapter 41. The Intestines: III. Neoplasms

Many different pathologic processes involving the mucosa result in polyps that project into the lumen of the intestine. Intestinal polyps may be foci of epithelial hyperplasia, epithelial neoplasms, hamartomas, or retention polyps. Not all polyps are associated with epithelial proliferation. Inflammation (inflammatory polyps), lymphoid hyperplasia (lymphoid polyps), and mesenchymal neoplasms (lipoma, leiomyoma) may also result in polyps (Table 41-1).

Table 41–1. Intestinal Tumors: Types and Relative Frequency.
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Table 41–1. Intestinal Tumors: Types and Relative Frequency.
Duodenum Jejunum Ileum Colon Rectum Appendix
Benign neoplasms
Tubular adenoma + + − + +++ ++ +
Villous adenoma + Rare Rare ++ +++ +
Leiomyoma + + + + + Rare
Others 1 Rare Rare Rare Rare Rare Rare
Nonneoplastic tumors
Hamartomatous polyp + ++ + + + Rare
Hyperplastic polyp Rare Rare Rare +++ +++ ++
Juvenile retention polyp Rare Rare Rare + +++ Rare
Lymphoid polyp + + ++ ++ ++ +
Inflammatory polyp + + + + + +
Malignant neoplasms
Carcinoma + 2 Rare Rare +++ +++ +
Carcinoid tumor + + ++ + ++ +++
Malignant lymphoma + + ++ + + +
Gastrointestinal stromal neoplasms + + + + + Rare

Rare = almost never occurs; + = occurs uncommonly; ++ = common; +++ = very common and characteristic location.

1 All rare; include neurofibroma, schwannoma, granular cell tumor, lipoma, hemangioma, lymphangioma.

2 Most duodenal carcinomas occur in the periampullary region.

Benign Neoplasms

Colonic Adenoma

Adenomas of the colon are present in 20–30% of all individuals over the age of 50 years. They are of two major types: tubular and villous (Figure 41-1). Colonic adenomas are associated with genetic mutations identical to those seen in colon cancer. The number of mutations in adenomas is less than in carcinoma but increases as the adenoma enlarges and becomes more dysplastic (the adenoma → carcinoma sequence).

Figure 41–1.
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Villous adenoma (A) and tubular adenoma (B) of the colon, with their malignant counterparts.

Tubular Adenoma (Adenomatous Polyp; Polypoid Adenoma)

Tubular adenomas account for over 90% of colonic adenomas. They are commonly multiple, with 10–20 lesions present in some patients, and are pedunculated with a well-defined stalk (Figures 41-1B and 41-2).

Figure 41–2.
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Pedunculated adenomatous polyp of the colon. Microscopic examination of the polyp and stalk is necessary to evaluate the presence of malignant change.

Histologically, a tubular adenoma is composed of benign neoplastic glands bunched together above the muscularis. The epithelial cells are hyperchromatic and stratified and show loss of normal mucin content (Figure 41-3)—sometimes termed “adenomatous change.” The proliferating epithelium may be composed of tubular glands (tubular adenoma) ...

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