Benign tumors of the large intestine
Adenomas of the colon constitute the great majority of polypoid lesions. The World Health Organization (WHO) has classified adenomas as (1) tubular, (2) villous, and (3) tubulovillous. Adenomas may be sessile, with a broad base, or have a large, thin pedicle containing fibrous tissue, blood vessels, and lymphatics. Polyps occur with greatest frequency in areas of the world where colonic cancer is common.
Most adenomas cause no symptoms. Bleeding from an adenoma may occur, more commonly with left-sided polyps. Bleeding usually is noted with bowel movements and is not profuse. Abdominal cramps may occur with large polyps. Intussusception of the large bowel from a benign adenoma is rare. Large villous adenomas may secrete copious amounts of potassium-rich mucus and cause diarrhea and hypokalemia when located in the distal large bowel.
It is estimated that 2% to 5% of single adenomas and 30% of villous adenomas become malignant, particularly if greater than 2 cm in diameter. Removing these benign tumors has been advocated as a means of preventing colonic cancer.
Data from the National Polyp Study indicate that removal of all colonic adenomas at colonoscopy markedly decreases the expected incidence of colon cancer. However, whether removal of diminutive polyps (
<0.3 cm) is essential remains controversial. After removal of all adenomas, surveillance colonoscopy at 3-year intervals seems adequate for most patients; adenomas that are found subsequently are usually small and tubular.
In familial polyposis coli and Gardner's syndrome, total proctocolectomy is recommended. In younger patients a subtotal colectomy with ileorectal anastomosis is sometimes performed, with endoscopic surveillance of the remaining rectum and fulguration of polyps at least twice yearly. However, because cancers have developed in the rectal segment, a great responsibility is placed on the physician when a proctocolectomy is not done. Ileoanal anastomosis is an option to avoid ileostomy if the rectum is removed.
Hyperplastic polyps should be differentiated from adenomas. They are characteristically small (often only 2 to 3 mm) mucosal excrescences that are usually smooth and sessile, although occasionally they have a short stalk. They appear most often in the rectosigmoid and seem unrelated to colonic neoplasia.
Juvenile polyps, usually pedunculated hamartomas, may be seen in adults as well as children. They may ulcerate and bleed or cause obstruction. With time they self-amputate spontaneously, but juvenile polyps that cause symptoms should be removed. Although there is no evidence that juvenile polyps undergo malignant change, the incidence of cancer of the colon appears to be higher in patients and family members of patients who have had juvenile polyps.
Carcinoid tumors may occur in the colon and especially the rectum. As with carcinoid tumors in the small intestine, only tumors greater than 2 cm in size tend to metastasize. Carcinoid syndrome does not occur in patients with metastatic rectal carcinoid tumors.
Leiomyomas may occur in the colon but are much less common there than in the small bowel and stomach. Lipomas are the second most common benign colonic tumors. They are usually submucosal, and more than half are near the ileocecal valve. Lipomas may cause intussusception but are usually asymptomatic. They have a characteristic low-density appearance on CT scan. At colonoscopy they are seen to have a yellowish color and a soft, springy consistency and can be easily indented with a biopsy forceps, producing a "cushion" or "pillow" sign. Lipomas are usually sessile and, if asymptomatic, should be left alone.
WHEN TO REFER
If the diagnosis of a small bowel tumor is made by radiologic examination, referral for gastrointestinal endoscopy may be appropriate for confirmation and histologic analysis. Most patients require surgical resection, but oncology referral may be appropriate as well for additional treatment of malignant small bowel neoplasms, most notably small bowel lymphoma.
Carcinoid tumors that appear to be resectable should be referred to an appropriate surgical specialist. Oncology referral should be obtained for patients with rapidly progressive metastatic carcinoid.
Patients at average risk for colorectal cancer can be screened successfully in the primary care setting. Patients with increased risk of colorectal cancer (those with first-degree relatives who have colorectal cancer or adenomas, a family history of familial adenomatous polyposis or hereditary nonpolyposis colorectal cancer, a personal history of colorectal cancer or adenomas, or long-standing inflammatory bowel disease) usually require more intensive screening, often involving periodic referral for colonoscopy. Colorectal adenomas should be removed at colonoscopy whenever possible. Patients with advanced colorectal cancer require expertise involving endoscopy, surgery, and oncologic treatment and should be referred to appropriate specialists as needed.
Author: Charles J. Lightdale
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