Computed tomographic (CT) colonography, also referred to as virtual colonoscopy, is providing local clinicians with a minimally invasive screening tool for detecting early colorectal cancer and polyps.
Christopher Meyer, MD, radiologist and member of the virtual colonoscopy team at Radiologic Associates of Fredericksburg, said gastroenterologists refer patients who have experienced incomplete optical colonoscopies. Physicians also refer patients with contraindications to optical colonoscopy, including the following: severe cardiac or pulmonary disease, as there is an increased risk with sedation; bleeding disorders or the inability to be taken off anticoagulation therapy; and/or known stricture or stenosis. In addition, the procedure provides clinicians with an option for screening patients who refuse to undergo conventional colonoscopy.
The efficacy and safety of virtual colonoscopy have been evaluated in a number of studies. Final results of the American College of Radiology Imaging Network National CT Colonography Trial, published in the Sept. 18, 2008 New England Journal of Medicine (NEJM), concluded that “…CT colonographic screening identified 90% of subjects with adenomas or cancers measuring 10 mm or more in diameter. These findings augment published data on the role of CT colonography in screening patients with an average risk of colorectal cancer.” Other key research includes a large-scale study by the University of Wisconsin School of Medicine, published in the Oct. 4, 2007 NEJM, which found that virtual colonoscopy and optical colonoscopy screening resulted in similar detection rates for advanced neoplasia.
Based on mounting research, the American Cancer Society, the American College of Radiology and the U.S. Multi-Society Task Force on Colorectal Cancer, which included representatives from three gastroenterology groups, added virtual colonoscopies to their lists of recommended tests in 2008.
“Virtual colonoscopy has become another important screening modality in the arsenal of procedures for detecting colon polyps and early colon cancer,” Dr. Meyer noted.
Virtual colonoscopy also allows radiologists to examine other intraabdominal organs. Occult intraabdominal malignancy, abdominal aortic aneurysms, renal stones, gallstones and intraabdominal adenopathy have all been identified using the procedure.
Patients with abnormal virtual colonoscopies often must undergo an optical colonoscopy later to evaluate or remove suspicious lesions and polyps. Therefore, virtual colonoscopies are intended for patients with an average risk of colorectal cancer and are contraindicated for patients with a history of polyps or colon cancer.
Other contraindications include the following: active rectal bleeding or other symptoms that suggest an increased likelihood of finding a polyp or cancer; acute diverticulitis, which increases the risk of perforation; active bowel inflammation (active ulcerative colitis, Crohn’s disease, diverticulitis, or inflammatory bowel disease, as it increases the risk of perforation); pregnancy; recent colectomy or polypectomy; lack of intact ileocecal valve or right hemicolectomy; absence of anorectum; and/or severe pain or cramping on the day of exam.
Experience and Training
RAF’s virtual colonoscopy team has performed the procedure for two years at Medical Imaging at Lee’s Hill in Fredericksburg. In addition to Dr. Meyer, team members include George Fish, MD; Jeffrey Frazier, MD; Stacy Moulton, MD; and Neil Patil, MD.
These physicians have all completed additional continuing medical education workshops, reviewed National Institutes of Health case files and/or received additional training through residency or fellowship programs. Their daily experience reading normal and abnormal abdominal CT scans also comes into play when evaluating virtual colonoscopies.
Virtual colonoscopy patients must undergo bowel preparations similar to those for optical colonoscopy, where the goal is a “clean, distended bowel” for the procedure, said Dr. Meyer. Patients meet with the group’s CT screening coordinator beforehand to receive instructions and items they will need for the prep.
A 40-slice CT scanner and a carbon dioxide (CO2) insufflator are used during the virtual colonoscopy, which takes approximately 20 minutes to complete. First, a catheter with an inflatable balloon tip is inserted into the patient’s rectum and filled slowly with CO2, regulated by an automatic turnoff. This ensures a well-distended bowel.
The patient then is scanned in the supine position and in the prone position. Resulting images are sent to the radiologists’ workstations, where axial and sagittal plane images are used to reconstruct a three-dimensional visualization—or “fly-through” —of the entire colon and rectum. Each virtual colonoscopy is read by two team members for improved accuracy, Dr. Meyer said.
Insurance companies may pay for diagnostic virtual colonoscopies in cases of incomplete colonoscopy, noted Carla Ford-Brooks, CT screening coordinator. Most insurance companies do not presently cover the cost if a patient is opting to have the procedure done as a screening, but may reimburse if the patient is referred due to a contraindication, including risks from coagulation therapy or anesthesia.