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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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