Medical Correspondent Dr Muiris Houston takes more than a passing interest in virtual colonoscopy
With a strong family history of colon cancer, I have been quietly postponing the inevitable: the need to start a personal screening programme for the disease through regular colonoscopy check-ups.
Why the reluctance? Don't thousands of Irish patients undergo the relatively simple procedure - involving the passage of a flexible telescope through the large bowel - every year? Yes, they do, but somehow it seems unnatural to volunteer for colonoscopy when you feel fine. It would be different if I had symptoms such as abdominal pain, unexplained weight loss or rectal bleeding. Then I would actively seek out the day procedure - and ask the specialist to give me a little extra sedation to block out any pre-imagined discomfort.
So, I have been following the progress of a group of researchers at the Mater hospital and Dublin City University with more that passing interest. They have been developing the technique of virtual colonoscopy - examining the colon in detail using advanced scanning techniques, without the need for the insertion of a telescope (see panel).
Dr Helen Fenlon, consultant radiologist at the Mater, returned from Boston with an established expertise in the area. Dr Paul Whelan runs the Vision Systems Laboratory (VSL) in Dublin City University, where advanced research into computer-aided diagnosis is carried out.
Dr Padraig McMathuna, consultant gastroenterologist at the Mater, is the other key member of the Mater Colon Cancer/VSL group. Following initial funding from the Irish Cancer Society and the Health Research Board, the group received a Science Foundation Ireland Investigation Programme Grant in 2002. Research grants of €683,000 enabled the researchers to develop virtual colonoscopy - known as colonography - to the point where it is now available to patients of the Mater Hospital. The installation of state-of-the-art "multi slice CT scanners" in both the Mater public and private hospitals has allowed Dr Fenlon to perform more than 500 CT colonography studies.
Patients who have had a difficult colonoscopy in the past, and older, frail people for whom the physical toll of a full colonoscopy is too much, are ideal candidates for virtual colonoscopy. Sometimes it can be difficult for gastroenterologists to visualise the entire colon using the flexible telescope; the virtual procedure can ensure the entire large bowel has been properly checked for cancer or polyps.
Colon cancer is unique in that many cases of the disease first start off as benign growths called polyps. As they grow, a percentage become malignant, leading to cancer of the large bowel. It is generally accepted that polyps greater than 1 cm need to be removed. Virtual colonoscopy has a 90 per cent accuracy for picking up growths of this size.
A landmark paper in the New England Journal of Medicine last December concluded "virtual colonoscopy . . . is an accurate screening method for the detection of colorectal cancer . . . and compares favourably with optical colonoscopy in terms of the detection of clinically relevant lesions".
Dr Fenlon shows me some images from a recently performed colonography. The clarity of the structures is incredible; the folds of bowel look just like the direct image seen through the colonoscope. The computer constructs three-dimensional images from those generated by the high-resolution CT scanner. Fenlon lists its advantages: no need for sedation or intravenous access, no complications, no risk of perforating the bowel, and the patient is under the scanner for just 10-15 minutes. Disadvantages include the need to clear out the bowel for 24 hours in advance of the procedure, and possible cramps caused by introducing air into the bowel. And if a suspect polyp is identified, then you will need to undergo a conventional colonoscopy in order to remove it.
"The value of virtual colonoscopy is that it eliminates the need for conventional colonoscopy in people with no disease. It selects those with abnormalities who would most benefit from the conventional examination," Fenlon says. And in music to my ears she adds: "Down the line, virtual colonoscopy will, in my opinion, become part of colorectal cancer screening."