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VIEWS: 34 PAGES: 21

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									  Virtual and Optical Colonoscopy:
Combining methods for effective colon
           cancer screening
            Objectives
Understand epidemiology of colon cancer
and current screening
Evaluate results of virtual colonoscopy
Understand advantages and
disadvantages of virtual CT
Raise further questions regarding future
use of virtual colonoscopy
           Epidemiology
Colon Cancer
2nd leading cause of cancer related death,
lifetime risk of 6%.
Approximately 60,000 deaths per year.
Known pathophysiology for cancer
 progression results in effective
           sceening.
Adenomas are a known precursor to invasive
colorectal adenocarcinoma. They double in size
every 10 years, allowing a window for detection
and cancer prevention.
 Adenomas are more common in older patients
(40-50% after age 60), as they take time to
develop and then grow, providing a defined
population to screen.
Three varieties of adenoma based on epithelial
architecture, with varying incidence and
malignant potential of each type.
                     Tubular Adenoma
    Most common adenoma, >90%. Cancer is rare in these
      lesions, but there is no way to determine malignancy
      grossly, so biopsy and pathology must be used.




http://www.endoatlas.com,
http://www-medlib.med.utah.edu/WebPath/GIHTML/GIIDX.html
           Tubulovillous Adenoma
 25-50% villous architecture on path. Malignant potential
   between tubular and villous adenoma




http://www.endoatlas.com,
http://www-medlib.med.utah.edu/WebPath/GIHTML/GIIDX.html
                   Villous Adenoma
 Least common adenoma. Most likely to be malignant, with
   40% of polyps with diameters of >4 cm found to be
   malignant




http://www.endoatlas.com,
http://www-medlib.med.utah.edu/WebPath/GIHTML/GIIDX.html
   Current Screening Guidelines
   USPTF suggests one or more of the
   following, for all adults >50 y/o;
       Annual FOBT
       Flexible simoidoscopy every 5 years
       Double contrast barium enema every 5 years
       Colonoscopy every 10 years



Pignone, Rich, et al. “Screening for Colorectal Cancer in Adults at Average Risk:
   A Summary of Evidence for the U.S. Preventative Task Force.” Annals of Int.
   Med, 137 (2);E132-E141, 2002.
     Current Screening Success
Only 53.1% of adults >50 y/o have had any sort of colon
cancer screening




Seeff, Nadel, Blackman et al. “Colorectal Cancer Test Use Among Persons Aged
>50 Years - United States, 2001.” MMWR, 52(10);193-196, 2003.
    Virtual CT Colonoscopy
First described in 1994, and until recently
only tested in populations with moderate-
high risk of colonic neoplasia.
It may be possible to replace invasive,
direct visualization of polyps via
colonoscopy with a less invasive, indirect
imaging technique.
  Virtual CT as a screening test in an
        average risk population
     First study done to screen an average risk
     population in 2003.
     Large (1233 patients), prospective study
     which compared virtual CT colonoscopy
     and same day conventional colonoscopy.
     Gold standard was unblinded conventional
     colonoscopy, where the endoscopist was
     told location of all lesions found on virtual
     CT after performing initial exam.
Pickhardt, Choi, Hwang et al. “Computed Tomographic Virtual Colonoscopy to
Screen for Colorectal Neoplasia in Asymptomatic Adults.” NEJM, 349 (23);
2191-2264, 2003.
                                Methods
     Used multi-detector CT, water soluble and
     barium contrast to tag remaining stool, and
     thereby remove from final image, and
     used 3D reconstructions for better
     visualization of bowel lumen
     6 experienced radiologists performed CT
     colonoscopy, and then immediately
     followed by conventional colonoscopy.

Pickhardt, Choi, Hwang et al.
                                Results
     Sensitivity of each test was compared through
     different size polyps.
   Size of polyp
                       10 mm        8 mm    6 mm
   Sensitivity of
   Virtual
                       93.8%        93.9%   88.7%
   Colonoscopy

   Sensitivity of
   Conventional
                       87.5%        91.5%   92.3%
   Colonoscopy




Pickhardt, Choi, Hwang et al.
                        Results (cont)




Fig A. Scout image identifying lesion in cecum of asymptomatic 55- y/o man. Fig B.
3D reconstruction of image.
Pickhardt, Choi, Hwang et al.
                       Results (cont)




Fig C. 2D CT image of same polyp. Fig D. Same polyp on optical colonoscopy.
Arrow is at appendiceal orifice.
Pickhardt, Choi, Hwang et al.
Conclusions from Pickhardt, Choi,
          Hwang et al.
Virtual colonoscopy is a reasonable
screening method which can detect
lesions as small as 6 mm with sensitivity of
88%.
Advantages to CT colonoscopy
Minimally invasive, with less risk of bleeding,
perforation, or anesthetic side effects.
May be attractive to the 50% of the population
which has thus far evaded traditional methods
for colon cancer screening.
No recovery time needed, making for a shorter
procedure.
Can find other incidental cancers.
Less likely to pick up non-adenomatous polyps.
Disadvantages to CT colonoscopy
Requires bowel prep.
Pneumocolon uncomfortable, and no sedation is
provided as in optical colonoscopy.
Once polyps are found they must then be
biopsied by optical colonoscopy.
Incidental findings may lead to unnecessary
procedures.
Requires coordination between radiology and
gastroenterology for same day colonscopy so
bowel prep is not repeated.
Directions for further research
If CT colonoscopy is widely adapted, then
a threshold size for polyps for biopsy and
removal by optical colonoscopy must be
determined.
Cost effectiveness should be determined.
622 out of the 1233 patients studied by
Pickhardt et al. would have required
optical colonoscopy for polyp removal if all
polyps were removed.
               Summary
Although not yet a USPTF accepted technique
for colon cancer screening, virtual CT
colonoscopy is emerging as a legitimate option.
Current uses include evaluation of patients who
were not able to undergo a full colonoscopy due
to obstucting cancer, but as techniques improve
and more radiologists gain experience virtual CT
may gain acceptance as a less invasive
screening method.
                           References
1.   Cotran, Kumar, Collins. Robbins’ Pathologic Basis of Disease, 6th ed. Philadelphia:
     W.B. Saunders Co, 1999. (826-830)
2.   http://www.endoatlas.com
3.   http://www-medlib.med.utah.edu/WebPath/GIHTML/GIIDX.html
4.   Lieberman, Weiss, Bond et al. “Use of Colonoscopy to Screen Asymptomatic
     Adults for Colorectal Cancer.” NEJM, 343 (3); 162-168, 2000.
5.   Pickhardt, Choi, Hwang et al. “Computed Tomographic Virtual Colonoscopy to
     Screen for Colorectal Neoplasia in Asymptomatic Adults.” NEJM, 349 (23); 2191-
     2264, 2003.
6.   Pignone, Rich, et al. “Screening for Colorectal Cancer in Adults at Average Risk: A
     Summary of Evidence for the U.S. Preventative Task Force.” Annals of Int. Med,
     137 (2);E132-E141, 2002.
7.   Seeff, Nadel, Blackman et al. “Colorectal Cancer Test Use Among Persons Aged
     >50 Years - United States, 2001.” MMWR, 52(10);193-196, 2003.

								
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