INTRODUCTION Colorectal carcinoma (CRC) is the Second most common cancer in United States and second leading cause of cancer related death Colorectal Cancer Incidence & Mortality 2000-2003 United States Kentucky African Americans Caucasians Incidence 64.4 53.1 61.2 Per 100,000 Mortality 28.4 19.8 23
INTRODUCTION The benign colorectal polyp is the core of colorectal cancer
HISTOLOGIC CLASSIFICATIONOF POLYPS Adenomas are one histologic subtype of colorectal polyps. Other histologic subtypes include mucosal polyps, hyperplastic/ serrated polyps, juvenile polyps, and inflammatory polyps. In addition, certain types of polyps can arise from layers deeper than the mucosa, including lipomas, carcinoid tumors, gastrointestinal stromal tumors (GIST), and serosal lesions.
HISTOLOGIC CLASSIFICATIONOF POLYPS. Adenomas constitute approximately half of colorectal polyps; hyperplastic and serrated lesions make up about one third or more; and mucosal polyps make up approximately 10%. The remaining histologic subtypes constitute only a tiny percentage. The histologic classification of polyps cannot be reliably determined by gross evaluation either at endoscopy or at CTC; they require pathologic examination for final diagnosis.
POLYP MORPHOLOGY. Polyps measuring 3 cm are generally divided into three major morphologic categories: sessile, pedunculated, and flat. Invasive masses are generally bulky annular or semiannular tumors.
The ideal target for screening and prevention of colorectal cancer is the “advanced adenoma,” which is defined as an adenoma that is large (10 mm) and/or contains histologic findings of either high-grade dysplasia or a prominent villous component
Methods for Screening Colonoscopy Air contrast barium enema CT colonoscopy
Clinical Indications for PerformingCTCSCREENING INDICATIONS Asymptomatic adults at average risk Asymptomatic patients with positive family history Asymptomatic patients at increased risk for colonoscopyDIAGNOSTIC INDICATIONS Following incomplete optical colonoscopy Evaluation of suspected submucosal lesions Surveillance of unresected 6-9-mm polyps detected at previous CTC Unexplained GI bleeding, iron deficiency anemia, or other GI symptoms Symptomatic patients at increased risk for colonoscopy Surveillance following resection of polyps or cancer
CTC TECHNICAL CONSIDERATIONSThe technique for CTC involves the following steps: (1) Bowel preperation. (2) Colon insufflation. (3) Image acquisition. (4) Image processing and interpretation.
Large fl at hyperplasticpolyp detected at CTC screening. 3Dendoluminal (A) and 2D transverse(B) CTC images show a large butrelatively subtle 15-mm nonpolypypoidlesion (arrowheads) within thetransverse colon. A central depressionis suggested on the 3D view. Thelesion was confirmed at same-day OC(C) and proved to be hyperplastic.
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) Air contrast barium enema: failed to identify up to 50% of polyps greater than 10mm in diameter
Virtual vs. Optical Colonoscopy Patients reported less discomfort with virtual colonoscopy Shorter examination time with VC 72.3% of patients preferred VC as screening technique compared to 5% preferred CC as screening technique More patients were willing to repeat a VC at shorter intervals than CC.
Benefits Of CT VirtualColonography Faster examination time and this is a non invasive test. It provides three-dimensional images that can depict many polyps and other lesions as clearly as when they are directly seen by optical Colonoscopy. Reduced patient risk, CT Colonography has a markedly lower risk of perforating the colon than conventional Colonoscopy.
Limitations of CT VirtualColonography CT Virtual Colonography is strictly a diagnostic procedure. If any significant polyps are found, they will have to be removed by conventional colonoscopy. The immediate risks of CTC include a small rate of perforation related to gas distension, which is lower than the risk from colonoscopy. Potential long-term risk from radiation exposure.