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VIRTUAL COLONOSCOPY

VIRTUAL COLONOSCOPY. DR DEEPIKA SOLANKI. Medical imaging procedure. Also known as CT colonography . Non invasive procedure. Uses X rays and computers. 2D and 3D images of rectum and entire colon with 3D reconstructed endoluminal views of the bowel. ACCEPTED INDICATIONS.

JasminFlorian
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VIRTUAL COLONOSCOPY

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  1. VIRTUAL COLONOSCOPY DR DEEPIKA SOLANKI

  2. Medical imaging procedure. • Also known as CT colonography . • Non invasive procedure. • Uses X rays and computers. • 2D and 3D images of rectum and entire colon with 3D reconstructed endoluminal views of the bowel.

  3. ACCEPTED INDICATIONS • Incomplete colonoscopy due to an occlusive mass or stricture preventing examination of the proximal colon. • Incomplete colonoscopy due to colonic tortuosity, adhesions, severe diverticular disease or patient intolerance of colonoscopy. • Inability to perform colonoscopy due to requirement for anticoagulant therapy or risks of sedation. • Patients who adamantly refuse to undergo colonoscopy but have a strong indication for diagnostic colonoscopy.

  4. CT COLONOSCOPY is under analysis as a screening tool for colorectal cancer because of its relative safety and greater patient acceptance as compared with other screening methods. • Follow up on colon cancer or polyps.

  5. Why Screen? • Best method for controlling colorectal cancer • 70-75% of CRC occurs in asymptomatic individuals • Detect and remove adenomatous polyps, precursor lesions for CRC, and detection of early stage carcinoma • Reduce mortality

  6. Barriers to Screening • Lack of health care coverage • Low education levels • Fear of pain • Fear of complications during procedure • Embarrassment of preparation process • Morbidly obese adults • Cost issues • Lost time from work • Lack of access

  7. Risk factors for CRC • Family history of colorectal cancer • Personal history of adenomas or ovarian/uterine cancer • Long standing IBD (8-15 years) • Environmental factors (diet and meds) • Lifestyle factors (physical inactivity, obesity, and cigarette smoking)

  8. Pathophysiology • Current belief is that most CRCs stem from preexisting adenomas • Adenomas that are large and/or have a villous component determine likelihood of containing invasive carcinoma • Polyps are slow growing and must grow for five years before they are clinically significant • Normal colonic mucosa is transformed into benign adenoma, followed by progression to polyp containing cancer, which can become invasive

  9. Methods for Screening • Colonoscopy • Flexible sigmoidoscopy • Air contrast barium enema • Fecal occult blood test (FOBT) • CT colonoscopy

  10. TECHNIQUE • COLONIC CLEANSING (pt needs to empty bowels by taking laxatives a day before the test) • COLONIC DISTENSION (done by using room air / carbon dioxide) • IMAGE ACQUISITION (done after colonic insufflation in supine and prone positions on a helical CT using low dose technique) • POST PROCESSING OF ACQUIRED DATA

  11. Intravenous contrast improves detection of medium sized polyps (6-9 mm) especially in a suboptimally prepared colon. • After acquiring supine and prone scans, various software packages are used to display images in both 2D and 3D (endoluminal) views.

  12. The table moves through the scanner to produce a series of 2 dimensional cross sections along the length of colon. • 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 prone position.

  13. CONTRAINDICATIONS • ALLERGY to contrast. • Suspected colonic PERFORATION. • Acute colonic INFECTION ( acute diverticulitis, severe infective colitis). • Acute lower GI BLEEDING. • Complete colonic OBSTRUCTION. • Very recent colonic SURGERY (<1 week). • MEDICALLY UNSTABLE patients. • REFUSAL to undergo colonic preparation.

  14. Detection Rates • Colonoscopy: Sensitivity of 88.2 (>10mm) Sensitivity of 90.0 (<6mm) • CT colonoscopy: Sensitivity of 92.2 (>10mm) Sensitivity of 85.7 (<6mm) • FOBT: detected 23.9% of advanced neoplasia • Flex Sig: 76% when used with FOBT • Air contrast barium enema: failed to identify up to 50% of polyps greater than 10mm in diameter

  15. Advantages • Virtual colonoscopy is less invasive, safer, and takes less time than a regular colonoscopy • A thin tube to insert air into the colon is placed in the rectum rather than long flexible tube that is moved up your colon. • Patients do not require sedation or anesthesia and can return home on their own or get back to work immediately after the test. • VC provides clearer, more detailed images. • Extra colonic findings.

  16. DISADVANTAGES • A radiologist cannot take tissue samples (biopsy) or remove polyps during VC, so a conventional colonoscopy must be performed if abnormalities are found. • May not show polyps smaller than 10 mm. • Exposure to radiation. • Slight risk of perforation while colonic distension.

  17. Virtual vs. Optical Colonoscopy • Patients reported less discomfort with virtual colonoscopy • Shorter examination time with VC • VC less embarrassing • More patients were willing to repeat a VC at shorter intervals than CC

  18. Conclusion • Not screening for CRC has great cost. • Very high detection rates in people with polyps over 5mm • Low detection rates for polyps less than 5mm could be acceptable because majority of polyps this size do not progress to CRC • Studies underway concerning technology advances that can affect the sensitivity and specificity for polyps and malignancy

  19. Conclusion (Cont.) • Studies with stool tagging and digital subtraction are going on to eliminate bowel preparation, which would increase patient acceptance

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