Virtual colonoscopy (also called CT colonography) is an imaging test that uses a CT scanner and computer software to create detailed 2D and 3D images of the inside of the colon and rectum.
It screens for polyps and colorectal cancer.
It is mainly used for colorectal cancer screening in average-risk adults generally starting at age 45.
Unlike a traditional colonoscopy, it does not involve inserting a long flexible scope through the entire colon.
A short, thin tube is placed only a short distance into the rectum to gently inflate the colon with air or carbon dioxide for clearer images.
The procedure typically takes about 10–15 minutes, requires no sedation or anesthesia, and most people can resume normal activities immediately afterward (including driving).
Computerized tomographic colonography after cathartic preparation and colonic distension.
Sensitivities for the detection of lesions 10 mm or more range from 32% to 90% depending upon the skill of the reader.
Detection of colorectal polyps and cancer approaches that of conventional colonoscopy.
CT colonography considered a valid alternative to colonoscopy for screening for colorectal cancer in the general population.
In an evaluation of 937 patients with 1-3 risk factors for colorectal cancer patients underwent CT colonography followed by colonoscopy on the same day and the virtual colonoscopy had an 85% sensitivity and 88% specificity for detecting advanced neoplasia (Regge).
Threshold for detection of a lesion 5 mm.
Pickardt and others evaluating 1233 asymptomatic patients revealed that three dimensional endoluminal display can achieve a 93.8% sensitivity and 96% specificity for polyps of at least 10 mm in diameter compared to colonoscopy.
Optical CT colonography misses 2-12% of polypoid lesions larger than 10 mm (Lieberman).
Advantages over conventional colonoscopy include less invasive, less costly, more safe, and equally sensitive for relevant pathology.
Drawbacks include continued need for cathartics and lack of therapeutic capabilities.
Used to avoid sedation.
Traditional colonoscopy is incomplete, difficult, or riskier, due to bleeding disorders, certain medical conditions, or inability to tolerate the full procedure.
Evaluation of the colon is needed after an incomplete optical colonoscopy.
It can incidentally detect issues outside the colon (such as in the kidneys, liver, or aorta) because it images the abdomen and pelvis.
Preparation is similar to traditional colonoscopy: a clear-liquid diet and bowel-cleansing prep the day before so the colon is empty.
Some protocols also use oral contrast for tagging residual stool.
Studies show virtual colonoscopy is highly accurate for detecting larger polyps (≥10 mm) and cancer—comparable to traditional colonoscopy in many trials (sensitivity often ~90% or higher for clinically significant lesions).
It is less sensitive for very small polyps (<6 mm) and some flat lesions.
Advantages:
Minimally invasive; much lower risk of colon perforation.
No sedation
Faster procedures out 15 minutes.
Can evaluate the entire abdomen/pelvis and detect extracolonic findings.
Often better tolerated by frail or high-risk patients.
Limitations / disadvantages: Cannot remove polyps or take biopsies during the same procedure and follow-up traditional colonoscopy may be required if findings are abnormal.
Involves low-dose ionizing radiation (typically equivalent to roughly 1–2 years of natural background radiation.
Screening interval is usually every 5 years if normal vs. every 10 years for traditional colonoscopy in average-risk people.
Same bowel prep is required as for colonoscopy.
Generally very safe. Main risks include: Rare perforation from colon inflation, but much lower than with traditional colonoscopy.
Low-dose radiation exposure.
Temporary bloating, cramping, or gas from the air/CO₂ that usually resolves quickly.
It is an accepted screening option for average-risk individuals.
People at higher risk (strong family history, certain genetic syndromes, inflammatory bowel disease, prior polyps/cancer) are usually advised to have traditional colonoscopy instead.