COLONOSCOPY

What is colonoscopy?

It is a safe, effective means of visually examining the full lining of the colon and rectum, using a long, flexible, tubular instrument. It is used to diagnose colon and rectum problems and to perform biopsies and remove colon polyps. Most colonoscopies are done on an outpatient basis with minimal inconvenience and discomfort.

Who should have a colonoscopy?

Your physician may recommend a colonoscopy exam if you have change in bowel habit or bleeding, indicating a possible problem in the colon or rectum.

A colonoscopy is also necessary to:

• Check unexplained abdominal symptoms
• Check inflammatory bowel disease (colitis)
• Verify findings of polyps or tumors located with a barium enema exam
• Examine patients who test positive for blood in the stool
• Monitor patients with a past history of colon polyps or cancer

How is colonoscopy performed?

The bowel must first be thoroughly cleared of all residue before a colonoscopy. This is done one to two days before the exam as prescribed by your physician.

The colonoscope is inserted and when possible will be advanced to the portion of the colon where the small intestine enters. During a complete examination of the bowel, your physician will remove polyps or take biopsies as necessary.

The entire procedure usually takes less than an hour. There is little pain; however, mild sedation is given when necessary to relieve anxiety and discomfort. Following the colonoscopy, there may be slight discomfort, which quickly improves with the expelling of gas. Most patients can resume their regular diet later that day.

What are the benefits of colonoscopy?

With colonoscopy, it is now possible to detect and remove most polyps without abdominal surgery. Colonoscopy is more accurate than an x-ray exam of the colon to detect polyps or early cancer. Frequently, polyps can be removed at the same time, a major step towards the prevention of colon cancer.

Computed Tomographic Virtual Colonoscopy

Submitted by: Dr. Anthony Senagore, Chair Technology Committee ASCRS

Virtual computed tomographic virtual colonoscopy (VCT) utilizes radiographic images obtained by CT technology for the purpose of rendering two and three-dimensional images of the colon. The technique is rapidly evolving and appears promising and an adjunct method to perform screening examinations for colorectal cancer. Patients still require a mechanical bowel preparation to remove solid stool and a period of time on a clear liquid diet. The colon is insufflated via a transanally placed tube using room air.

The patient is imaged and a computerized software program extracts the images of the insufflated colon, generates an automated centerline for navigation and subtracts the opacified residual fluid in the lumen. The observer is then able to perform a virtual "fly-thru" of the colon. Use of both two and three-dimensional visualization optimizes identification of polyps and other lesions.

Early evaluations of VCT have been limited, based primarily upon the use of two dimensional views. The recent study by Pickhardt et al (NEJM 2003; 349:2191-2200) reported a sensitivity of 93.8% for polyps >7mm and 88.7% for adenomatous polyps at least 6mm in diameter. The sensitivity and specificity in this study was equivalent to optical colonoscopy. VCT identified two malignant polyps, one of which was missed at optical colonoscopy. The authors also commented that the rate of extra-colonic lesions in an average risk patient is <50% of high risk groups which reduces the potential for unnecessary investigations as a result of the VCT. Another report by Iannaccone et al (Radiology 2003; 229:775-781) reported 100% sensitivity for cancers, 100% for polyps >1cm, and 83% for polyps 6-9 mm. These authors were able to reduce the radiation exposure by using a multi-detector device (1.8-2.4 mSv compared to 4.4-6.7 mSv in other studies). Taylor et al (Radiology 2003; 229:782-790) reported an absence of hemodynamic changes during VCT compared to a 30 fold increase in hypotension and a higher rate of bradycardia with optical colonoscopy.

VCT appears to offer significant promise as a screening modality in moderate risk populations. It avoids the need and risks for sedation, avoids the risk of instrument perforation with optical colonoscopy, and compares favorably for time consumption (15 minutes for image acquisition and at best, under ideal circumstances, 15 minutes for interpretation). Optimal VCT requires a multidetector CT scanner for high speed and better resolution. The downside is that patients require mechanical bowel preparation and those with a suspected lesion will either need to be referred for an optical colonoscopy or arrangements will need to be made for on-demand colonoscopy of positive tests. Further data is required to support full transition of screening for colorectal cancer to VCT. The additional CT resources, technicians and radiologists will be significant as well. 

_______________________________________________________________

The executive office of the 2,600-member American Society of Colon and Rectal Surgeons is located in the Chicago suburb of Arlington Heights. Board-certified colon and rectal surgeons complete a residency in general surgery, plus an additional year in colon and rectal surgery. They also pass an intensive examination conducted by the American Board of Colon and Rectal Surgery administered after successful completion of written and oral examinations conducted by the American Board of Surgery.

For additional information, please contact:

American Society of Colon and Rectal Surgeons
85 W. Algonquin Rd., Suite 550
Arlington Heights, IL 60005
(847) 290-9184 or (800) 791-0001
Or you can email them directly.

Back