Virtual colonoscopy
http://www.allieddiagnostics.net/specialities/virtual-colonoscopy/
What is virtual colonoscopy?
Virtual colonoscopy is a minimally invasive alternative to conventional colonoscopy (endoscopy) that screens the colon and rectum for polyps and early cancer before symptoms occur. Polyps are small masses of cells that grow out of the lining of the colon and rectum and can become cancerous over time. Detecting clinically significant polyps and cancer early with virtual colonoscopy allows for treatment at a stage when disease can be prevented or cured, before it spreads to other parts of the body.
At Allied Diagnostics Virtual colonoscopy involves no scopes, sedation, recovery time, or referral from your doctor or insurance plan. It is performed on a High Definition Volume Computed Tomography (VCT) scanner which takes up to 600 two-dimensional (2D) and three-dimensional (3D) images of the colon in just 10-15 seconds. The combination of 2D and 3D images increases the radiologist’s ability to detect and analyze areas of concern. The 3D images allow the radiologist to reconstruct the colon and do a ‘fly-through’ of its entire length, simulating the views of conventional colonoscopy.
What is the difference between conventional colonoscopy and virtual colonoscopy?
| Conventional Colonoscopy | Virtual Colonoscopy |
|---|---|
| Takes 30 minutes. | Takes 5 minutes. |
| Preparation includes oral laxative and clear diet 24 hours before procedure. | Preparation includes oral laxative and clear diet 48 hours before procedure. |
| Sedation delivered intravenously with a needle. | No sedation. |
| Insertion of a long, flexible scope into the rectum that is guided up the length of the colon. | Minimally invasive insertion of a small, disposable tube two inches inside the rectum to fill the bowel with CO2. |
| Scope can only view the inner surface of the colon directly ahead and cannot examine narrow areas or both sides of folds in the bowel. Cannot determine exact location of a polyp. | The 3D fly-through allows the radiologist to turn, zoom, and rotate the view in forward and reverse motion, which helps visualize complex folds or narrow areas of the colon. Polyps can be located exactly, marked, and measured electronically. Both the inner and outer surface of the colon plus the surrounding organs can be seen. |
| Polyps can be removed immediately. | Clinically significant polyps must be removed through conventional colonoscopy. |
| 10% of patients have a failed colonoscopy. | Used with patients who have had a failed colonoscopy. |
| Risk of perforation (1 in 500 to 1000). | No risk of perforation. |
| Long recovery from sedation with a missed day of work. | No recovery period and no missed day of work. |
Why is screening for colorectal cancer important?
In its early stages, colorectal cancer causes no symptoms in the patient. Most colorectal cancers begin as small precancerous (adenomatous) polyps that can take 3 to 10 years to progress to cancer. Approximately 8% to 12% of untreated polyps become cancerous tumors. The risk of a polyp becoming cancerous is related to its size. A polyp smaller than 5 mm has essentially no risk of becoming cancerous, whereas a 10 mm to 20 mm polyp has a 10% risk, and those larger than 20 mm have a 30% or greater risk.
When screening is performed regularly, polyps can be removed before they have the chance to become cancerous. Removal of precancerous polyps is essential and has the potential to reduce the incidense (new cases) of colorectal cancer by 40%. The 5-year survival rate for patients with tumors localized to the bowel is 90%. For tumors that spread to parts of the body outside the colon, the five-year survival rate is 8%. If a patient is already experiencing symptoms of colorectal cancer, there is a 50% chance that the pathology is advanced, making the survival rate low.
Who is at risk for colorectal cancer?
During the course of a lifetime, 1 in 20 individuals will develop colorectal cancer. Individuals over age 50 account for 90% of cases of colorectal cancer. This is because the risk of developing colorectal cancer increases significantly with age. For example, the probability of a U.S. male developing colorectal cancer is 1 in 1508 from birth to age 39, 1 in 115 from age 40 to 59, and 1 in 25 once he has reached age 60. Similarly, the probability of developing this disease increases for women as they age. A woman’s risk of developing colorectal cancer is 1 in 1719 between birth and age 39, 1 in 145 between ages 40 and 59, and 1 in 33 between ages 60 and 79.
Risk factors for colorectal cancer besides age include:
- History of colorectal cancer or adenomatous polyps
- Family history of polyps
- Certain genetic traits
- History of chronic bowel disease
The lifetime risk of developing colorectal cancer is 8 times greater for individuals who have a first-degree relative (i.e. parent, sibling, child) with the disease. A genetic syndrome called Familial Cancer Syndrome is known to increase a person’s likelihood of developing colorectal cancer at an earlier age. Inflammatory bowel disorders (e.g. Crohn’s disease, ulcerative colitis) increase a person’s risk 30-fold.
Modifiable risk factors for colorectal cancer include obesity, physical inactivity (less than 3 hours per week), poor dietary habits, smoking, and excessive alcohol consumption (more than 1 drink per day). Individuals with these and the above risk factors should consider screening before age 50. However, as many as 75% of colorectal cancer cases occur in people with no known risk factors.
Can colorectal cancer be prevented?
Screening for colorectal cancer is important because there is no way to completely prevent the disease. According to the American Cancer Society, regular screening and certain lifestyle choices (eg, nutrition, physical activity) can greatly reduce the risk of developing colorectal cancer. Regular screening has been shown to reduce risk by at least 33%. Lifestyle choices thought to decrease the risk of colorectal cancer include:
- Maintaining an ideal body weight
- Eating a healthy diet that includes:
- 5 or more servings of vegetables and fruit a day
- whole grains
- foods high in calcium
- a limited consumption of high-fat dairy products, fried food, and red meat
- Refraining from smoking or excessive alcohol intake (more than 1 drink per day)
- Regular exercise (30 minutes or more of moderate exercise per day, or 1 hour of brisk walking per day)
Who should have virtual colonoscopy?
Virtual colonoscopy is recommended for men and women over age 40 with a family history of colorectal cancer, and for all individuals over age 50 regardless of risk factors. This procedure is ideal for individuals who have had an incomplete or failed colonoscopy or who cannot tolerate the conventional method.
How accurate is virtual colonoscopy?
Although more studies are being conducted, recent studies show that virtual colonoscopy is equivalent to conventional colonoscopy in its accuracy for detecting polyps 10 mm or larger. Research shows that only 1% of polyps smaller than 1 cm will develop invasive cancer.
A study conducted at Boston University School of Medicine found that virtual colonoscopy’s rate of detection for polyps increased with size and was similar to conventional colonoscopy when polyps were larger than 6 mm. Virtual colonoscopy’s sensitivity for detecting polyps was 82% for polyps 6mm to 9mm, and 91% for those 10mm or larger. Polyps measuring 1mm to 5mm were correctly located and identified 55% of the time. Virtual colonoscopy detected 100% of colorectal cancers. In the largest and most recent study on virtual colonoscopy, researchers at the University of California at San Francisco reported a sensitivity of 80% for polyps measuring 6mm to 9mm and 90% for polyps 10mm or larger. Studies at the Mayo Clinic showed that virtual colonoscopy’s sensitivity for detecting 1cm polyps was 85%.
What are the limitations of virtual colonoscopy?
Because virtual colonoscopy is not performed with a scope, polyps cannot be immediately removed and must be followed-up with conventional colonoscopy. Most studies indicate that polyps less than 1cm rarely become cancerous. Therefore, the medical community is questioning the need to remove every polyp found during conventional colonoscopy regardless of its size. Polyps smaller than 1cm that are detected with virtual colonoscopy can be identified and tracked on follow-up examinations to see if they have grown. This avoids the unnecessary removal of polyps and risks associated with conventional colonoscopy. This viewpoint is supported by a recent screening study of colorectal cancer conducted by the Veterans Administration of 3500 asymptomatic adults. Data showed that only 10% of patients required therapeutic colonoscopy.
Another limitation of virtual colonoscopy is that it is harder to detect small, flat adenomas. Although uncommon, these tumors may harbor a more rapid, invasive cancer. Studies are still being conducted to determine virtual colonoscopy’s ability to detect these adenomas.
For preparation information please read our Patient guides.
