Colonoscopy: A Guide to Endoscopic Screening and Therapy

By D. BRADY PREGERSON, MD—Series Editor | September 1, 2008

Dr Pregerson is a staff emergency medicine physician at Cedars-Sinai Medical Center in Los Angeles and at Tri-City Medical Center in Oceanside, Calif. He is also a clinical instructor in medicine at the University of California, Los Angeles, School of Medicine and the designer of ERPocketBooks.com, a medical Web site designed for health care providers who work in emergency medicine and urgent care.

SHAI FRIEDLAND, MD and TONYA KALTENBACH, MD
Dr Friedland is assistant professor of medicine in the division of gastroenterology and heptatology at Stanford University School of Medicine in Stanford, Calif, and a staff physician at the Veterans Administration Palo Alto Health Care System in Palo Alto, Calif. Dr Kaltenbach is a staff physician at the Veterans Administration Palo Alto Health Care System.

FINDINGS AND TREATMENT

Figure 9 – In this photograph, a snare is positioned around a diminutive polyp. The snare can now be retracted into the white plastic sheath, cutting the polyp off. It is also possible to apply electrocautery through the snare while cutting the polyp, although cautery is not necessary for diminutive lesions such as this.

The focus in screening colonoscopy is on finding premalignant adenomas. Most adenomas are polypoid; thus, they are usually visualized as protruding bumps of varying sizes surrounded by flat normal mucosa (see Figure 5). Some, however, are flat or depressed lesions (Box).

Small adenomas. Diminutive adenomas, less than 5 mm in diameter, are the most common. These are usually easily removed using either a biopsy forceps or a snare. Many experts now favor using a snare without cautery for diminutive lesions (Figure 9).

Large adenomas. Larger polyps, which can be sessile or pedunculated, are usually removed using a snare with monopolar cautery. The snare is positioned around the lesion and then retracted into a plastic sheath while monopolar cautery is applied (electric current travels through the snare to a grounding pad applied to the patient’s buttock or back). The current helps the snare cut through the tissue and also ensures some destruction of adenomatous cells at the resection margin. More advanced techniques are also widely used; these include clip application to prevent bleeding and submucosal saline injection to separate the lesion from the underlying muscle of the colon wall before resection. Since not all endoscopists are experienced in these techniques, patients may be referred to specialty centers for resection.

Nonadenomatous polyps. These are also frequently found in the colon. In the rectum and sigmoid, diminutive hyperplastic polyps are exceedingly common (Figure 10). These lesions have no malignant potential. Adenomatous polyps are usually redder than hyperplastic polyps and typically have a surface appearance reminiscent of brain, with sulci and gyri (see Figure 5).

Figure 10 – A diminutive hyperplastic polyp is seen slightly to the left of the center of this image. It is slightly paler than the surrounding normal mucosa and contains numerous circular crypts, indicating that it is hyperplastic rather than a precancerous adenoma

Hyperplastic polyps are typically pale and usually have a regular pattern of circular or stellate pits at the surface (see Figure 10). Before the development of highresolution scopes, many of which now have various proprietary imaging modes that accentuate the surface features of the mucosa, it was difficult to accurately distinguish between hyperplastic and adenomatous polyps, so all visualized polyps were typically removed. This practice is evolving as endoscopic diagnosis progresses, and more selective removal may soon become the norm.

Carcinomas. Colorectal adenocarcinomas are usually obvious, appearing as large masses (often several centimeters in diameter) that frequently have an ulcerated surface. Multiple forceps biopsies are generally performed to facilitate tissue diagnosis before surgery. More unusual malignancies, such as lymphomas, can also be diagnosed with forceps biopsies. Rarely, infectious ulcers, Crohn disease, or ischemia can have the appearance of an ulcerated mass; in this setting, the tissue samples obtained on biopsy do not demonstrate malignancy. Other findings. These include diverticula, colitis, arteriovenous malformations, and surgical anastomoses.

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by ed smith | April 05, 2011 11:15 PM EDT

A withdrawl time of 6 minutes? For the "avergae"colon of 5 and 1/2 feet in length? This has to be a joke; if not just forget colonoscopy. Sedation? Why subject patients to the mind-numbing effects of midazolam when you can take a little extra time and do a better exam unsedated? Pne of my frients (a FP MD) still has significant memory loss from 4mg of midazolam given for her colonoscopy...she's a wreck from this "common" drug. I'm sorry that I recommended colonoscopy for her.

COLONOSCOPY: PITFALLS & PEARLS

•When selecting a preparation agent, keep in mind that polyethylene glycol causes comparatively few electrolyte derangements and fluid shifts and is thus relatively safe even in patients with renal failure or other comorbidities. Although sodium phosphate can result in kidney injury, fluid shifts, and electrolyte imbalances, many patients find this agent more palatable.

•Decisions regarding discontinuation of the use of platelet inhibitors and anticoagulants can be complex. Guidelines are available at http://www.asge.org; however, in many cases, the decision may need to be individualized.

•After negotiating several turns, the colonoscope may no longer move forward smoothly. If you try to advance it further in this situation, there is a tendency for the loops in the colon to enlarge and for the tip to remain stationary rather than moving forward as desired. In fact, advancing the scope in the presence of a loop can result in perforation. A variety of maneuvers can be used to reduce the loops. These include withdrawing the scope while applying torque to the shaft in either a clockwise or a counterclockwise direction; repositioning the patient onto his or her back, stomach, or right side; and having an assistant apply pressure to strategic locations on the abdomen.

•To reach the cecum in some patients, you may need to change to a thinner scope (pediatric scope) or occasionally a longer scope (enteroscope).

•The appendiceal orifice, visualization of which serves as a marker for the cecum, is visible even in patients who have had an appendectomy.

•While withdrawing the scope, considerable back and forth motion is usually required to inspect behind all of the many folds of the colon, as well as to lavage and suction fluid residue in areas that have not been adequately cleansed.

•Because the rectum is difficult to fully inspect with the scope in the standard position, it is customary to retroflex the scope in the rectum.

•Many experts now favor using a snare without cautery to excise small adenomas, less than 5 mm in diameter, which are the most common size of adenomas encountered.