Virtual colonoscopy

This page was reviewed under our medical and editorial policy by

Toufic Kachaamy, MD, Chief of Medicine, City of Hope Phoenix

This page was reviewed on January 17, 2022.

A virtual colonoscopy, also called a computed tomography (CT) colonography or CTC, is an imaging test used to visualize the digestive system and screen for colorectal cancer.

The digestive system is one long tube that flows through the body. Food enters the mouth and moves into the stomach, which empties into the small intestine. The small intestine empties into the large intestine. The large intestine is made up of the colon and rectum and ends with the anus.

During a virtual colonoscopy, a computer program analyzes images from X-rays and builds three-dimensional (3D) pictures of the inside of the colon and rectum. A doctor reviews these images to highlight potentially abnormal areas of the colon, where polyps or cancer or precancerous lesions may be growing.

Why your doctor may suggest a virtual colonoscopy

Doctors may recommend a virtual colonoscopy:

  • To screen for colon and rectal cancer
  • To diagnose other digestive diseases, causes of abdominal pain, changes in bowel movements or unexplained weight loss
  • To identify the reasons for anemia or blood in the stool 

Colorectal cancer screening guidelines vary depending on whether a patient is average or high-risk.

A virtual colonoscopy is one of several ways to screen for colon cancer. The least invasive colon cancer screening option is a stool test, which analyzes feces for signs of cancer. The most invasive test is a colonoscopy, which uses a tube to visualize the entire colon, requiring complete bowel preparation (prep) and sedation. A less invasive, but similar, test is the flexible sigmoidoscopy, which visualizes only the lower third of the colon.

The virtual colonoscopy fits somewhere between a stool test and a full colonoscopy in terms of discomfort and invasiveness. It requires full bowel prep, but doesn’t require sedation. Inform the doctor if you have a pacemaker or other implanted device that may interfere with the imaging—your doctor may recommend another screening option.

Regular colon cancer screening is essential to find and treat any polyps and cell mutations early (potentially before they become cancer). If a virtual colonoscopy is the screening option that works for you, the doctor may recommend scheduling one every five years. Virtual colonoscopy may have several benefits over a regular colonoscopy, including:

  • It can be performed more quickly.
  • It typically does not include medications or anesthesia.
  • It’s less invasive.
  • It may be better than a regular colonoscopy in reaching narrow or blocked parts of the intestine.
  • It may be an option for patients who cannot undergo a regular colonoscopy because of swelling, bleeding or breathing issues.

Virtual colonoscopy prep

You should be able to continue taking medications as usual, but it’s important to verify with your doctor. You may need to stop taking iron supplements or anything that may make it harder to see the bowels.

Before undergoing a virtual colonoscopy, you'll prepare the colon and rectum by emptying them completely. Colon prep is usually done through a combination of medications and diet.

To clean out the bowels:

  • You may have to go on a clear liquid diet for a day or more leading up to the procedure. A clear liquid diet means only clear bouillon or broth, gelatins, coffee or tea without milk or creamer, fruit juices, sports drinks and water.
  • You may need to take medications to prepare the colon, a combination of laxatives and enemas that may cause diarrhea and empty the bowels. It may be uncomfortable, but it’s essential for getting clear images during the procedure.

The night before the appointment, you may need to drink a special solution called contrast to highlight any remaining feces and differentiate it from colon polyps and lesions.

On the day of the appointment, dress comfortably (no tight waistbands) and remove any jewelry, as the imaging machines are sensitive to metals.

During the procedure

The test typically happens in an imaging room with a computed tomography (CT) scanner, typically in the radiology department of a hospital or outpatient medical center. The procedure takes about 10 to 15 minutes and typically isn’t painful.

First, you may be asked to lie in the fetal position on a table that goes into the imaging machines. The rectum and colon are filled with air using a small tube inserted into the anus. The air may make you feel uncomfortably bloated and cause gas pains and cramping.

After flipping onto your back, the table slides into the scanner. During imaging, the technician may ask you to hold your breath and stay still for 15 seconds. You may have to do this twice in two positions to get clear pictures: once on your back, and then on your side or stomach.

Risks and side effects of virtual colonoscopy

The risks and complications of getting a virtual colonoscopy are low. It’s possible but extremely unlikely that the inflation could injure or puncture the colon or rectum. This is a risk for any invasive colon screening, including a flexible sigmoidoscopy or a full colonoscopy.

You may experience nausea, vomiting, bloating or rectal irritation from the contrast medicine used for the test. The imaging test also exposes you to a small amount of radiation, so notify your doctor if you’re pregnant or think you may be pregnant—and discuss the possibility of a different procedure.

After the procedure

Following the imaging test, you may feel bloated from the air in the intestines and may feel some cramping. But most patients are able to resume normal activities right away.

Post-procedure, seek medical care immediately if you experience any of these symptoms:

  • Significant, severe stomach pain
  • Fever
  • Dizziness
  • Weakness
  • Bowel movements that are bloody
  • Bleeding that’s coming from the anus

Reviewing the results

Normal results mean the intestinal tract is healthy. Abnormal results may indicate polyps, tumors, precancerous lesions or cancerous growths in the intestines. A virtual colonoscopy may also detect diverticulosis (abnormal pouches on the intestines), colitis (inflamed intestines from a digestive disease), ulcers or other digestive problems.

If possible abnormalities have been identified, a full colonoscopy may be recommended to take samples and potentially remove any growths.

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