Department of Radiology resumes CT colonography services

These studies, also called CTC or virtual colonoscopy, offer a minimally invasive examination of the colon and are an alternative to optical colonoscopy (OC) for colon cancer screening particularly in cases where OC is contraindicated or unable to be performed or completed.

The study requires a prep equivalent to that utilized in OC.  In addition, tagging agents (Barium sulfate and Gastrografin) are administered the day before CTC to enable identification of any residual stool and fluid.  At UNC hospitals the prep and instructions are mailed to patients by outpatient pharmacy.

The study utilizes pressure controlled distension of the cleansed colon with carbon dioxide via a small bore catheter placed in the rectum.  CT images are then obtained in both supine and prone positions and computer processed to provide multiplanar and 3D reconstructions.  These are evaluated by the radiologist for luminal deforming lesions such as polyps or most cancers.  Truly flat lesions can be difficult to detect but are thought to be uncommon in a western population.  CTC is also not felt to have sufficient sensitivity and specificity for lesions less than 6 mm and these are not routinely reported or felt to be clinically relevant.   Radiation exposure is generally less than that of a single abdomen pelvic CT.  Please note that because of the low dose nature of the exam and the absence of IV contrast, evaluation of the extracolonic organs is limited and CTC should not be considered an adequate replacement of the standard abdominal pelvic CT.

Present guidelines from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer and the American College of Radiology recommend CTC as a screening test beginning at age 50 and continuing on a q 5 year basis.  At present screening (no symptoms present)  and diagnostic (performed for symptoms) CTC is covered by BlueCross Blue Shield of NC.   Medicare will pay only for diagnostic CTC performed after an incomplete colonoscopy.  Self pay options run approx $1500-2300 for both professional and technical charges.

Questions regarding CTC can be addressed to Drs. Joseph KT Lee or David Warshauer or our CTC technologist - coordinators at 843-6254.

Recent review articles and commentary have appeared in  Radiology (Pickhardt et al, Colorectal Cancer:  CT Colonography and colonoscopy for  detection - Systematic review and meta-analysis, Radiology 2011, 259:393-405),  and Am . J  Gastroenterol . (Burke et al.  CT Colonography: Ready for Prime Time? , Am J Gastroenterol,  2010 105: 2128-2138.)  Guidelines are discussed in Levin et al, Screening and Surveillance for the Early Detection of Colorectal Cancer and Adenomatous polyps, 2008:  A Joint Guideline from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology, CA Cancer J Clin 2008; 58:130-160.

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