CT Colonography (Virtual Colonoscopy)

CT colonography, also known as virtual colonoscopy, uses a low-dose CT scanner to produce two and three-dimensional images of the large bowel after it has been cleaned and gently inflated with gas. A radiologist then navigates through the images to look for polyps and cancers, without a scope being passed around the colon.

It detects cancers and polyps of 1 cm or more about as well as conventional colonoscopy, with no sedation and a very low complication rate. It cannot remove polyps or take biopsies, so roughly 1 in 10 people will need a colonoscopy afterwards. It is less sensitive for small and flat lesions.

What CT Colonography (Virtual Colonoscopy) shows

The images show polyps, generally reported from 6 mm upwards, colorectal cancers, narrowed segments, and diverticular disease. Because a full bowel wall view is obtained, it can examine the colon above a tight stricture or in a segment that a colonoscope could not reach. The scan also covers the abdomen and pelvis at low dose, so it sometimes reveals findings outside the bowel, such as an aortic aneurysm, kidney masses or enlarged lymph nodes; most incidental findings are harmless, but some lead to further tests. It does not show fine mucosal detail, so colitis, tiny flat lesions, angiodysplasia and small polyps under 6 mm are better seen on optical colonoscopy.

When CT Colonography (Virtual Colonoscopy) is recommended

• Incomplete colonoscopy because of a tortuous bowel, adhesions or a narrowing
• People for whom sedation or colonoscopy is risky: frailty, significant heart or lung disease, or anticoagulants that are difficult to stop
• Bowel cancer screening for average-risk adults who decline colonoscopy, typically every 5 years
• Symptoms such as a change in bowel habit or anaemia in older patients, as an alternative route to exclude cancer
• Examining the rest of the colon when a tumour blocks the passage of a scope

Limits and situations where another test is better:

• Active inflammatory bowel disease, acute diarrhoea or acute diverticulitis, where inflating the bowel carries a perforation risk
• A high likelihood of needing polyp removal, for example a positive stool blood test, polyposis syndromes or Lynch syndrome: go directly to colonoscopy
• Pregnancy
• Within about a week of a deep biopsy or polyp removal, or soon after bowel surgery
• Rectal bleeding that may come from the anal canal or haemorrhoids, which CT does not assess well

How to prepare

• A low-residue diet for 1 to 2 days, then clear fluids the day before
• A laxative preparation, often milder than for colonoscopy; reduced-laxative regimens exist for frail patients
• An oral contrast drink (iodine or barium based) with meals to tag leftover stool and fluid, so it can be told apart from polyps
• Tell staff about iodine allergy, diabetes medicines, kidney disease and glaucoma or prostate or heart problems, which influence whether a muscle relaxant is used
• You can drive afterwards, since there is no sedation

What happens during the test

You lie on the scanner table and a thin, soft tube is placed a few centimetres into the rectum. Carbon dioxide is introduced by an automated pump, which causes a bloated, crampy feeling. An injection of a bowel relaxant such as hyoscine may be given. Scans lasting 10 to 20 seconds each are taken with you lying on your back and then on your front or side, holding your breath. Intravenous contrast is sometimes added in patients with symptoms. You are in the room for 15 to 25 minutes. The carbon dioxide is absorbed quickly, so bloating settles within an hour or so.

Results and next steps

A specialist radiologist needs 20 to 30 minutes or more to read the study. Reports are usually ready in 1 to 3 days, and some centres offer same-day reading so that a colonoscopy can follow while your bowel is still prepared. A normal result usually means a repeat in 5 years for screening. Polyps of 6 to 9 mm lead to colonoscopy or surveillance, and polyps of 10 mm or more, or masses, lead to colonoscopy with removal or biopsy. Incidental findings are reported with advice.

• Test time: 15 to 25 minutes
• Results ready: 1 to 3 days; same day in some centres
• Back to everyday activity: None

Safety and risks

• Cramping and bloating during the test
• Bowel perforation, in about 1 in 3,000 or fewer, and lower in screening populations
• Radiation of roughly 1 to 5 mSv, comparable to 1 to 2 years of natural background radiation
• Faintness, blurred vision or a dry mouth from the relaxant injection
• Incidental findings causing anxiety and additional tests
• Missed small or flat polyps

Arranging CT Colonography (Virtual Colonoscopy) in Türkiye

A reasonable part of a check-up visit, especially if colonoscopy has failed or is unsuitable for you. The preparation begins 1 to 2 days beforehand, so plan for that in your hotel. Ask whether same-day colonoscopy is available if a polyp is found, which avoids doing the bowel preparation twice. Ask for the images on disc to take home.

Send your previous reports and the question you want answered and a Clinic-Y coordinator replies within 24 hours with suitable teams and written, all-inclusive proposals side by side. Reviewing your case is free.

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