___________________________________________________________________________ Colorectal Cancer
Adenoma Detection . Missed adenoma detection is strongly associated with failure to prevent colorectal cancer during multi-year follow-up colonoscopy trials, and most interval colorectal cancers are due to missed lesions and incomplete polypectomy. The marked variation in colonoscopist adenoma detection rates within practice groups, and the essential role of adenoma detection in colorectal cancer prevention led to adenoma detection as a performance target [144; 145; 146]. The examination is considered adequate if detection of polyps >5 mm is unimpeded. In screening colonoscopies of asymptomatic, average-risk persons, a minimum adenoma detection target rate of 25% is recommended. Adenoma detection rates of less than 25% indicate that performance improvement steps should be initiated. Adenoma detection rate is considered the primary measure of mucosal inspection quality and is the single most important quality measure in colonoscopy. Colonoscopists with high adenoma detection rates clear colons better, and patients with precancerous lesions are brought back earlier for their next colonoscopy. Colonoscopists with low adenoma detection rates fail to identify patients with precancerous lesions and multiple lesions, placing these patients at elevated risk for cancer from inappropriately long intervals between colonoscopy [142]. Withdrawal Time . The time taken to remove the colonoscope after cecum intubation (excluding time for biopsies or polypectomy) is termed withdrawal time, and colonic mucosa should be carefully examined for polyps during scope withdrawal. The recommended colonoscope withdrawal time should be at least six minutes in colorectal cancer screening of patients without previous bowel surgery (when no biopsies or polypectomies are performed) [142]. Numerous studies have demonstrated increased detection of significant neoplastic lesions in colonoscopic examinations with an average withdrawal time of at least six minutes, and longer withdrawal time is associated with higher detection rates [147; 148; 149]. Correction of Poor Performance . The objective for measuring quality indicators is to improve patient care by identifying poor performers for retraining or removal of their privileges to perform colonoscopy if performance cannot be improved. Most quality indicators are amenable to improvement. An exception may be withdrawal time; despite overwhelming evidence that withdrawal time is positively associated with detection, imposing longer withdrawal times on colonoscopists has not been found effective [142]. Computed Tomographic Colonography CT colonography, also termed virtual colonoscopy, involves examination of computer-generated colorectal images constructed from abdominal CT imaging that simulate a conventional colonoscopy. Pre-procedure laxatives are required to clean the colon, and the colon is insufflated with air just prior to the CT examination, which may be uncomfortable [150]. The risk of complications is extremely low because the test is non-invasive. CT colonography is now in use to perform
screening and diagnostic imaging in patients with incomplete colonoscopy or for whom colonoscopy is contraindicated. Randomized trials are in progress comparing CT colonography with immunochemical FOBT (iFOBT) and colonoscopy, and should produce valuable information concerning patient acceptance, diagnostic yield, and costs [120; 151]. Potential Complications and Harms Specificity for polyp detection is consistently high with CT colonography, but the broadly variable sensitivity requires confirmatory colonoscopy for findings suggestive of colorectal cancer. Another disadvantage with CT colonography is the inability to remove polyps [152]. Extracolonic abnormalities are common in CT colonography, most commonly renal, splenic, uterine, hepatic, ovarian, pancreatic, and gallbladder abnormalities. Very little information is available on the clinical value of their detection or the impact on patient anxiety and psychologic function [153; 154]. One study found CT colonography to be a useful diagnostic tool in patients who previously underwent incomplete optical colonoscopy [155]. Flexible Sigmoidoscopy Flexible sigmoidoscopy involves anal insertion of a sigmoidoscope (similar to the colonoscope) to visualize the rectum and sigmoid colon—the lower one-third of the colon. The scope inflates the large bowel with air to improve imaging, and polyp removal or biopsy may be performed during the procedure [156]. A 60-cm flexible sigmoidoscope was introduced decades ago that is more tolerable to patients than the older, rigid sigmoidoscope. It allows a more complete distal colon examination and can discover up to 65% of polyps, compared with 25% using the older instrument [157]. Potential Complications and Harms Sigmoidoscopy can be an uncomfortable or painful procedure. Women may have more pain during the procedure, which may discourage them from returning for future screening sigmoidoscopies. Sigmoidoscopy can also cause perforation of the colon, bleeding, severe abdominal pain, and death, although this is rare [84; 156]. Bleeding and perforation are the most common complications. Most cases of bleeding occur in patients who have polyps removed [156]. Double-Contrast Barium Enema Double-contrast barium enema (DCBE) consists of the patient receiving an enema with a barium solution. Air is then pumped into the colon, and a series of x-rays are performed to image the entire colon and rectum [158]. Potential Complications and Harms DCBE is no longer recommended as an alternative test for colorectal cancer screening, and its use has declined dramatically. DCBE effectiveness for polyp detection is substantially lower than that of colonoscopy and CT colonography [115].
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