Colorectal Cancer Study : Part 2

by National Cancer Institute

(Page 2 of 3)

Overall, patients' thoughts are similar and positive for both CT colonography (virtual colonoscopy) and traditional colonoscopy, with less favorable thoughts about bowel preparation. Most patients state that they would prefer virtual colonoscopy for future evaluation.

A newer examination for detection of colorectal abnormalities is CT colonography, or "virtual colonoscopy." Computer-simulated three-dimensional images are used to examine the mucosal surface of the colon and a two-dimensional view is used to visualize the structure of the colon. This non-invasive alternative offers several advantages to the patient over colonoscopy: no need for sedation or monitoring of vital signs and no recovery period. Disadvantages are that the conventional bowel preparation program is still needed and that the insufflation (blowing gas into the colon to enlarge the area) is uncomfortable.

A total of 120 patients were recruited for this study. The patients who were included had an increased risk of colorectal abnormalities, due to; suspected polyps, rectal bleeding, blood in the stool, history of prior polyps, or a family or personal history of colorectal cancer. These patients received virtual colonoscopy followed by a traditional colonoscopy on the same day.

The study showed that for both virtual colonoscopy and traditional colonoscopy, patients' thoughts after the procedure were more favorable than what was expected. Patients expressed more favorable thoughts about colonoscopy for pain and embarrassment with most responses being "none" to "a little" for both exams. Overall appraisals of the tests were favorable and similar between colonoscopy and virtual colonoscopy. Patients mainly expressed "not unpleasant" to "a little unpleasant." Overall appraisal of the bowel preparation was the most negative.

Subjects who have undergone screening flexible sigmoidoscopy (FSG) and were found to have non-advanced adenomas (pre-cancerous polyps) in the lower portion of the colon have a similar risk for advanced abnormalities in the upper portion of the colon as subjects with no adenomas in the lower colon. Subjects with advanced adenomas in the lower colon, however, are at an increased risk. Patients found to have these abnormalities were referred for a colonoscopy to examine the upper portion of the colon.

Sigmoidoscopy is used to view the lower (distal) portion of the colon. When physicians find an abnormality in this area, studies have suggested that it is predictive of abnormalities in the upper (proximal) portion of the colon. Therefore, these patients are referred for a colonoscopy which is able to view the entire colon.

A total of 8,802 patients underwent a full colonoscopy within one year of an abnormal baseline flexible sigmoidoscopy in PLCO, with two-thirds of those patients having a follow-up colonoscopy within three months. Subjects with advanced adenomas in the distal colon were found to be at increased risk for having advanced adenomas in the proximal colon; however, subjects with only non-advanced distal adenomas were not at increased risk for advanced proximal adenomas. Specifically, 12 percent of subjects with advanced distal adenomas, 4 percent of subjects with (only) non-advanced distal adenomas, and 4 percent of subjects with no distal adenomas were found to have advanced proximal adenomas.

In a group of patients who were found to have many polyps, radiologists were in agreement that virtual colonoscopy and traditional colonoscopy identified the same problems.

The evaluation of computed virtual colonoscopy as a non-invasive examination of the colon continues to face new challenges. Early estimates of the diagnostic performance of virtual colonoscopy have been promising but variable.

The purpose of this study was to evaluate reader agreement by a radiologist for colorectal polyp detection in a group of patients who had many polyps. This group of patients, who were suspected of having polyps, was first examined with virtual colonoscopy and then traditional colonoscopy the same day. The images were analyzed independently by four experienced radiologists.

A total of 157 colorectal lesions ranging from 4 millimeters to 30 millimeters were found at colonoscopy and correlated with virtual colonoscopy findings. Overall analysis demonstrated a 75 percent agreement among the four readers.

Approximately 70 percent of individuals who undergo screening sigmoidoscopy are satisfied and find the procedure more comfortable than expected, and only 15 percent to 25 percent find the procedure unpleasant. Physicians should not project discomfort to patients as a reason for not requesting screening sigmoidoscopy.

Physicians often cite patient discomfort as a reason for not requesting sigmoidoscopy, but patient experiences have not been well-studied. The researchers for this study adapted a survey which was designed to measure satisfaction with screening mammography. Questions about screening using flexible sigmoidoscopy centered on convenience, accessibility, staff interpersonal skills, physical surroundings, perceived technical competence, pain and discomfort, expectations and beliefs, and general satisfaction.

A total of 1,221 patients were surveyed after sigmoidoscopy. The results show that over 93 percent of the participants strongly agreed or agreed that they would be willing to undergo another examination, and 74.9 percent would strongly recommend the procedure to their friends. Regarding pain and discomfort, 76.2 percent strongly agreed or agreed that the examination did not cause a lot of pain, 78.1 percent stated that it did not cause a lot of discomfort, and 68.5 percent thought that it was more comfortable than expected. Fifteen percent to 25 percent of the patients indicated they had a lot of pain, great discomfort, or more discomfort than expected. Women were more likely to have significant pain or discomfort than men.

Among experienced abdominal radiologists using virtual colonoscopy, the ability to find polyps was similar with 2-D and 3-D (two dimensional and three dimensional) display techniques, although individual cases showed improved results with 3-D display techniques. Evaluation of reader agreement (independent radiologists detecting the same abnormalities) demonstrated good agreement for 3-D display, but not as good for 2-D display.

Virtual colonoscopy is a rapidly growing and evolving technology for the detection of colorectal polyps and permits viewing with 2-D and 3-D display techniques. This method is being used as a potential noninvasive alternative for the detection of colorectal polyps.

Virtual colonoscopy was performed on 16 patients who were suspected of having polyps at a prior flexible sigmoidoscopy examination or barium enema examination. Three specific 2-D and 3-D display techniques were tested. Three experienced abdominal radiologists independently analyzed each test case and each patient was retested six weeks later.

The results of readings 1 and 2 were similar for both 2-D and 3-D techniques among the readers. Overall observer agreement was good for the 3-D display techniques; however, observer agreement for 2-D techniques was lower.

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