Laboratory Studies
Complete blood cell count
A low hemoglobin level and a classic low mean cell volume (MCV) suggest iron deficiency anemia, but these values can be within reference ranges or can be considered nonspecific findings if small polyps are present.
Iron studies
Obtain ferritin levels, serum iron levels, and transferrin saturation values. Patients with iron-deficiency anemia have low ferritin and serum iron levels and low transferrin saturation.
Fecal occult blood testing
Only 20-40% of patients with adenomas have positive test findings, usually resulting from distal and larger polyps. Of those patients with fecal occult blood, 5-10% have colon cancer. Annual screening by fecal occult blood testing results in reduced mortality from colon cancer.
Fecal occult blood testing is demonstrated in the video below.
Genetic studies
Genetic studies are not performed routinely in the evaluation of sporadic polyps.
DNA from colon cancer is shed into the fecal stream in greater quantities than DNA from normal colonic mucosa. Studies are ongoing for detection of multiarray assay for common mutations in colon cancer, including APC, p53, K-ras, and BAT-26 mutations. Unfortunately, most detected cases have been advanced tumors. This screening test has the potential of noninvasiveness and ease of use.
Imaging Studies
Double-contrast barium enema
Double-contrast barium enemas have a higher sensitivity compared to single-contrast barium enemas. Sensitivity increases with polyp size.
Compared to colonoscopy, barium enema detected 32% of polyps smaller than 6 mm in diameter, 53% of polyps between 6 mm and 10 mm, and 48% of polyps larger than 10 mm. A false-positive rate of 5-10% is found because of improper cleaning of the bowel. Diverticulosis or redundant bowel can result in a false-negative rate of 10%, especially in the rectosigmoid. The accuracy of the procedure also can have an element of operator-dependence.
For all structural evaluations of the large bowel, use sigmoidoscopy with a barium enema.
Computed tomographic colonography (virtual colonoscopy)
Computed tomographic colonography is a newer method that is not as sensitive as colonoscopy, although it has the advantage of being less invasive. This scanning still requires bowel preparation.
A large variability exists in the effectiveness of computed tomographic colonoscopy as a screening tool. Differences in studies are due in part to differing computed tomographic technologies. Historically, when compared to colonoscopy, computed tomographic colonography was able to identify 55-93.8% of all polyps larger than 1 cm, 71-88.7% of polyps between 0.5 cm and 0.9 cm, and only 39% of polyps smaller than 0.6 cm. [16, 17] Newer techniques using multidetector CT scanner, advanced software, and cathartic and tagging agents in bowel preparation are yielding significantly improved results. [18] More studies comparing colonoscopy with virtual colonoscopy are needed before making firm recommendations regarding the role of virtual colonoscopy in screening for colon polyps. [19]
Upper GI series and small bowel follow-through
These studies detect small bowel adenomas and can help investigate the small bowel for polypoid lesions beyond the reach of the conventional upper endoscope. They also help detect mass abnormality in 50-80% of patients and can help successfully define neoplasms in 30-44% of patients.
Video capsule endoscopy
Video capsule endoscopy has provided an increasingly effective method to assess the small bowel. Video capsule endoscopy is not used as a screening tool for colonic polyps.
Procedures
Endoscopy
Endoscopy is the most sensitive method of diagnosing polyps, and it also allows therapeutic intervention. See the images below.
Villous Adenoma. Endoscopic view of a sessile polyp, which histology studies revealed to be a villous adenoma. Courtesy of H. Chaun, MD.
Villous Adenoma. Endoscopic view of a sessile polyp histologically determined to be a villous adenoma. Courtesy of R. Enns, MD.
Villous Adenoma. Endoscopic view of injection of saline into the base of a sessile polyp histologically determined to be a villous adenoma. This enables an easier polypectomy. Courtesy of R. Enns, MD.
Villous Adenoma. Polypectomy with a snare around a sessile polyp base (villous adenoma) injected with saline. Courtesy of R. Enns, MD.
Adequate bowel cleansing is necessary prior to many procedures. Several preparations are marketed for bowel cleansing (eg, polyethylene glycol 3350 [GoLYTELY, NuLYTELY], magnesium citrate [Citroma], senna [X-Prep]) in preparing patients for surgery or gastrointestinal procedures, such as endoscopy, colonoscopy, and barium x-ray studies.
Bowel cleansing preparations may be used with various dietary preparations (eg, clear liquid diet 1-2 d before surgery or procedure) and are convenient to administer on an outpatient basis.
Colonoscopy
Colonoscopy is the most accurate method for detection of polyps and is the first-line procedure of choice. The sensitivity for detecting polyps by colonoscopy compared to double-contrast barium enema is 94% and 67%, respectively. Although accuracy is operator-dependent, colonoscopy is regarded as the criterion standard. [20, 21, 22]
Villous adenomas at colonoscopy are usually bulky, sessile, soft, velvety, and friable. However, colonoscopic appearance is not diagnostic of histology.
Chromoendoscopy and magnifying endoscopy techniques use dye or magnification to identify and classify the pit pattern of small lesions. This allows a more predictive model on the final histology. [23, 24]
Difficulties with colonoscopy include patient discomfort, the need for patient sedation, and material risks of complications (eg, perforation, hemorrhage). Colonoscopy also costs more to perform than barium enema. Note that the accuracy of colonoscopy findings is operator-dependent, with reports of missing up to 15% of small polyps (< 8 mm) in a tandem study. No large polyps were missed in this study.
Risk of perforation is less than 0.1%. After colonoscopic polypectomy, the risks of perforation and significant bleeding are 0.2% and 1%, respectively.
Esophagogastroduodenoscopy is used to help investigate for small bowel adenomas. Visualization of the duodenum is limited.
Enteroscopy is used to help investigate for small bowel adenomas. Visualization beyond the conventional endoscope (occasionally up to the ileum) depends on the skill of the operator.
Endoscopic retrograde cholangiopancreatography is used to help investigate for adenomas at the ampulla of Vater and allows for biopsy and therapeutic procedures if biliary obstruction is a concern. The risk of complicating pancreatitis is reportedly 3-5%.
Sigmoidoscopy
Flexible sigmoidoscopy allows for evaluation of the distal bowel to 60 cm. Compared to the previously used rigid sigmoidoscope, the flexible one can detect up to 3 times more adenomas, primarily because it can be inserted further.
Some guidelines recommend flexible sigmoidoscopy every 3-5 years in conjunction with annual FOBT for the screening of colon cancer. Overall, the role of flexible sigmoidoscopy is becoming increasingly limited in the screening and diagnosis of colon cancer. Patients do not require full bowel preparation.
Histologic Findings
Adenomatous epithelium has abnormal cellular differentiation with hypercellularity and variable amounts of mucin. The predominant cell type is columnar epithelium, and immature goblet cells may be observed. The dysplastic cells demonstrate elongated nuclei, are hyperchromatic, and have a picket-fence appearance.
Villous histology is characterized by glands arranged in long fingerlike fronds from the polyp surface down to the polyp stroma. Projections usually extend straight down with minimal or no branching. See the images below.
Villous Adenoma. Histology of villous adenoma. Fingerlike projections stretching from the surface of a polyp downward with minimal branching. Courtesy of D. Owen, MD.
Villous Adenoma. Histology of villous adenoma. Low-grade dysplasia with loss of mucin, prominent nucleoli, and hyperchromatic and elongated cells. Courtesy of D. Owen, MD.
Staging
Dysplasia is subdivided into mild, moderate, and severe categories. Note the following:
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Mild dysplasia is characterized by uniform loss of mucin and hyperchromatic and elongated cells. Glands appear branched and budding.
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Moderate dysplasia has more prominent nucleoli with increased crowding of cells.
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In severe dysplasia, increased nuclear pleomorphism, prominent and numerous nucleoli, and increased nuclear-to-cytoplasmic ratio occur. With continued cell proliferation, glands appear to form within glands, with a disordered cribriform appearance, and appear as carcinoma in situ.
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Villous Adenoma. Endoscopic view of a sessile polyp, which histology studies revealed to be a villous adenoma. Courtesy of H. Chaun, MD.
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Villous Adenoma. Endoscopic view of a sessile polyp histologically determined to be a villous adenoma. Courtesy of R. Enns, MD.
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Villous Adenoma. Endoscopic view of injection of saline into the base of a sessile polyp histologically determined to be a villous adenoma. This enables an easier polypectomy. Courtesy of R. Enns, MD.
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Villous Adenoma. Polypectomy with a snare around a sessile polyp base (villous adenoma) injected with saline. Courtesy of R. Enns, MD.
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Villous Adenoma. Histology of villous adenoma. Fingerlike projections stretching from the surface of a polyp downward with minimal branching. Courtesy of D. Owen, MD.
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Villous Adenoma. Histology of villous adenoma. Low-grade dysplasia with loss of mucin, prominent nucleoli, and hyperchromatic and elongated cells. Courtesy of D. Owen, MD.
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Villous Adenoma. Fecal occult blood testing. Video courtesy of Therese Canares, MD; Marleny Franco, MD; and Jonathan Valente, MD (Rhode Island Hospital, Brown University).
