Virtual colonoscopy

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Ct colonography
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Virtual colonoscopy
CT colonography of a rectal mass. Left image is a volume rendering and right image is a thin slice. It also shows the rectal tube used for insufflation of gas to distend the colon.
MeSHD023881
MedlinePlus007253

Virtual colonoscopy (VC, also called CT colonography or CT pneumocolon) is the use of

colon (large intestine), from the lowest part, the rectum, to the lower end of the small intestine, and to display the images on an electronic display device.[1][2] The procedure is used to screen for colon cancer and polyps, and may detect diverticulosis
. A virtual colonoscopy can provide 3D reconstructed endoluminal views of the bowel. VC provides a secondary benefit of revealing diseases or abnormalities outside the colon.

Procedure

This video shows a virtual colonoscopy of the rectosigmoid colon performed in a retrograde fashion. There is a 10-mm colonoscopically-proven polyp in the sigmoid colon seen at the top of the frame at the midpoint of the movie. The movie concludes at the tip of the rectal tube which was used to insufflate the colon.

While preparations for VC vary, the patient will usually be asked to take

consultant radiologist), viewing the 3D images to effectively subtract the left-over faeces, which may otherwise give false positive results.[citation needed
]

VC takes place in the

sedatives.[citation needed
]

During the procedure:[citation needed]

  • The patient is placed in a supine position on the examination table
  • The patient may be given a dosage of
    Butylscopolamine
    intravenously to minimize muscle activity in the area.
  • A thin tube is inserted into the rectum, so that air can be pumped through the tube in order to inflate the colon for better viewing.
  • The table moves through the scanner to produce a series of two-dimensional cross-sections along the length of the colon. A computer program puts these images together to create a three-dimensional picture that can be viewed on the video screen.
  • The patient is asked to hold his/her breath during the scan to avoid distortion on the images.
  • The scan is then repeated with the patient lying in a prone position.

After the examination, the images produced by the scanner must be processed into a 3D image, +/- a fly through (a cine program which allows the user move through the bowel as if performing a normal colonoscopy). A radiologist evaluates the results to identify any abnormalities.

The patient may resume normal activity after the procedure, but if abnormalities are found and the patient needs conventional colonoscopy, it may be performed the same day.[3]

Advantages

VC may be more comfortable for some individuals, as it does not require the use of a colonoscope. As a result, no sedation is needed, and the patient can return to his/her usual activities or go home after the procedure without the aid of another person. The lack of sedation also lowers the risk of the procedure since some people may have adverse reactions to sedative medications used during conventional colonoscopy. VC provides clearer, more detailed images than a conventional x-ray using a

barium enema, sometimes called a lower gastrointestinal (GI) series. Further, about 1 in 10 patients will not have a complete right colon (cecum) evaluation completed with conventional colonoscopy.[4] It also takes less time than either a conventional colonoscopy or a lower GI series.[5]

VC provides a secondary benefit of revealing diseases or abnormalities outside the colon.[6] One study of asymptomatic adults undergoing routine VC found that approximately one unsuspected extracolonic cancer was detected per 300 screenings in addition to about one invasive colorectal cancer per 500 screenings, for an overall rate of approximately one unsuspected cancer of any type detected per 200 screenings. Invasive colorectal cancer was the most common malignancy detected, followed by renal cell carcinoma.[7]

Disadvantages

During virtual colonoscopy, it is not possible to take tissue samples (biopsy) or remove polyps, so a conventional colonoscopy must be performed if abnormalities are found.[8] Also, VC does not show as much detail as a conventional colonoscopy, so polyps smaller than between 2 and 10 millimeters in diameter may not show up on the images.[9] Furthermore virtual colonoscopy performed with CT exposes the patient to ionizing radiation, on the order of a milligray.[10] Some research has demonstrated that ultra-low dose VC can be just as effective in demonstrating bowel disease due to the great difference in x-ray absorption between air and the tissue comprising the inner wall of the colon. Optical colonoscopy is taken as the "gold standard" for colorectal cancer screening by the vast majority of the medical and research communities. However, some radiologists recommend VC as a preferred approach to colorectal screening. Virtual colonoscopy is favored by some professionals because it permits complete visualization of the entire colon, hence providing more opportunity to identify precancerous polyps and cancer, and to then do prompt diagnostic biopsies or therapeutic removal of these lesions.[citation needed]

Alternatives

MRI colonography (MRC) allows similar visualizing without radiation exposure. It can detect larger adenomas and neoplasia with high specificity, but less sensitivity than conventional colonoscopy.[11]

Notes

  1. PMID 16361129
    .
  2. S2CID 22167728
    .
  3. ^ "Virtual Colonoscopy" Archived 2014-10-09 at the Wayback Machine - National Digestive Diseases Information Clearinghouse - NIH
  4. S2CID 12918901
    .
  5. ^ Virtual Colonoscopy - Mayo Clinic. "Virtual colonoscopy is typically faster than traditional colonoscopy. A scan of your colon takes about 10 minutes. Expect the entire virtual colonoscopy procedure to take 20 to 30 minutes."
  6. PMID 16040909
    . Retrieved 2008-12-22.
  7. PMID 20308446
    .
  8. ^ "Virtual Colonoscopy". National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), US. Retrieved 11 December 2018.
  9. ^ Findings presented at the American College of Gastroenterology annual scientific meeting in Las Vegas, Nev. An abstract of the study was printed in the September 2006 issue of The American Journal of Gastroenterology.
  10. S2CID 20987597
    .
  11. PMID 23415805
    .

References

External links

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