Computed tomographic colonography (CTC), sometimes called "Virtual Colonoscopy," is a non-invasive and well-tolerated CT scan, which uses an X-ray to create images of the body. The images are transferred to a computer, creating a detailed picture of the inside of the colon, so that a doctor can search for polyps or other abnormalities that may need to be removed.
A Prospective Evaluation and Classification of Extra-Colonic Abnormalities Identified with Computed Tomographic Colonography Screening in Asymptomatic, Average Risk Individuals [Abstract 209]
Computed tomographic colonography (CTC) screening is becoming a more prevalent option used to screen moderate-risk individuals for colon cancer. Because of the computer assisted technology, this procedure can also detect extra-colonic abnormalities, such as calcified arteries and nodules. This study examined the characteristics of the abnormalities found by the screening and the resulting evaluation and treatment.
The research team from the National Naval Medical Center conducted CTC for cancer screening on 979 asymptomatic, average risk patients and recorded extra-colonic abnormalities, categorizing the findings as critical (requiring therapeutic intervention), moderate (requiring additional diagnostic intervention) or incidental (no further action).
Extra-colonic abnormalities were detected in approximately 16 percent (156 pts) of CTC screenings, the most common being coronary artery calcifications (41 pts) and non-calcified pulmonary nodules (33 pts). Abnormalities were found throughout the body, including the heart and lungs, kidney, liver, bone and other organs. While half (51.6 percent) were classified as incidental, another 33 percent were moderate and 15 percent were critical.
"Significant abnormalities requiring further action accounted for nearly half of the abnormalities we found, suggesting that by screening for colon cancer, we may offer early detection of other potentially morbid conditions in some patients," said Brooks Cash, M.D., of the National Naval Medical Center, and senior author of the study. "However, it is important to note that abnormalities detected by CTC also increase the indirect costs associated with the exam, so we need to evaluate the true outcomes associated with these findings before recommending the routine use of this procedure."
Accuracy of Computed Tomographic Colonography for Colorectal Cancer (CRC) Screening in Asymptomatic Individuals [Abstract 278]
In an attempt to improve rates of screening while maintaining accuracy, researchers have been examining the optimal usage of computed tomographic colonography (CTC) screening, a less invasive and time consuming screening process. Studies have previously suggested that CTC was comparable to optical colonoscopy (OC), and interim results from this study support those findings.
For the current study, researchers recruited participants who were asymptomatic and at average risk for colon cancer. A total of 760 patients have undergone CTC since the start of the study. If the CTC identified a polyp larger than 10 mm or more than three polyps larger than 6 mm, participants underwent same-day OC, while patients with one or two polyps measuring 6-9 mm underwent OC after one year, and patients with no polyps greater than 6 mm had OC within five years. The one year delay in the removal of polyps is a novel feature of this trial, one which the investigators hope will be able to glean some information regarding the natural history of colonic polyps in this patient population.
Findings from the study suggest that CTC is, in fact, comparable in accuracy to OC in detecting polyps larger than 10 mm, with an overall detection sensitivity of 96.4 percent compared to 96.3 percent with OC. While CTC sensitivity falls as polyp sizes get smaller, CTC detection of smaller polyps (6-9 mm in size) was comparable to that of OC with an 83.6 percent accuracy (sensitivity=77.3 percent, specificity=85 percent). OC sensitivity for these polyps was 88.2 percent.
"For patients who are not at high risk for colon cancer or who do not have alarming signs or symptoms, CTC is an effective method to screen for precancerous colorectal lesions at our institution," said Brooks Cash, M.D., of the National Naval Medical Center, and lead author of the study. "However, for patients who are at increased risk or whose screening results are unclear, we still recommend the use of optical colonoscopy to properly evaluate their colon health. It is also important to realize that we are at the vanguard of this technology and our results may not be indicative of the results that would be obtained in the general community. CTC remains an innovative practice that needs more study before it can be widely recommended, though our current results are certainly very promising."
Histopathology of Small Polyps Removed in the Videoendoscopic Era [Abstract T1344]
Colorectal polyps are common in most of the adult population over 50 and while many are benign, others have the potential to develop into cancerous tumors. Current practice standards call for close monitoring of polyps under 1.0 cm, but do not require that these polyps be removed as a precautionary measure. Study authors from the Indiana University Medical Center closely evaluated more than 10,000 polyps under 1.0 cm and found that if all of these polyps are ignored, a substantial majority of colorectal neoplasms will be left in place to grow. Researchers examined 8,798 (81.6 percent) polyps that were smaller than 6.0mm and an additional 1,282 polyps that were between 6.0 mm and 9.9 mm. Analysis showed that almost half of the polyps smaller than 6.0 mm were either adenomas or advanced adenomas (49.86 percent). This rate was even higher for polyps between 6.0 mm and 9.9 mm; adenomas made up 58.7 percent of these polyps and an additional 5.7 percent were advanced adenomas.
"If we move to a policy of leaving polyps less than one centimeter in place, as has been suggested by some experts for patients who undergo virtual colonoscopy, then we'll be leaving more than 90 percent of the neoplasms in the colon in place," said Douglas Rex, M.D., of the Indiana University Medical Center and senior author of the study. "This would be a major paradigm shift in our colorectal cancer prevention strategy, which currently is based on colonoscopy with resection of all detected neoplasms. As such, it requires very careful evaluation."
Impact of a Virtual Colonoscopy Screening Program on Optical Colonoscopy in Clinical Practice: One Year Data [Abstract 288]
Since the introduction of virtual colonoscopy (VC), its potential impact on the use of traditional optical colonoscopy (OC) has been cause for much speculation. University of Wisconsin Medical School researchers have conducted the first "real life" analysis of the effects of VC on utilization rates of OC and found that while there has not been a decrease in the number of OC procedures performed, there has been a significant reduction in OC referrals.
Study authors reviewed data from the three month period before VC screening was introduced at the University of Wisconsin hospital; the period three months before to five months after VC was introduced; the 14 month period after the introduction of VC; and, finally, the six to 14 month period after VC screening was initiated. Period T4 is defined as the time when VC screening has reached its "steady-state," marked by an increase in VC procedures performed and an increase in provider and patient knowledge of the procedure. The average number of OC screenings performed each month did not change significantly after VC was introduced and the percentage of OC involving removal of polyps also remained constant. However, the percentage of OC screening referrals decreased significantly, from 247 per month to 203 per month after VC screening was initiated. According to the researchers, the trend may be an early indicator that there will be an eventual decrease in demand for OC screening.
"This study shows a potential change in the tide of colonoscopy choices. As more medical institutions and health care service providers adopt and reimburse for virtual colonoscopies, we may see a significant decrease in the popularity of more traditional colonoscopy techniques," said Darren C. Schwartz, M.D., University of Wisconsin Medical School and lead study author. "However, differences in accuracy do still exist so it is important for patients and their physicians, especially those at high risk for colon cancer, carefully consider their options when choosing a screening technique."
Digestive Disease Week® (DDW) is the largest international gathering of physicians, researchers and academics in the fields of gastroenterology, hepatology, endoscopy and gastrointestinal surgery. Jointly sponsored by the American Association for the Study of Liver Diseases (AASLD), the American Gastroenterological Association (AGA), the American Society for Gastrointestinal Endoscopy (ASGE) and the Society for Surgery of the Alimentary Tract (SSAT), DDW takes place May 20-25, 2006 in Los Angeles, California. The meeting showcases more than 5,000 abstracts and hundreds of lectures on the latest advances in GI research, medicine and technology.
Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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