The role of MR colonography for colorectal cancer screening.

Abstract

M OST COLORECTAL cancers (CRCs) develop over a period of several years from adenomatous polyps. ~ This pathogenesis makes CRC to a large extent preventable. Detection and removal of polyps eliminates the risk of subsequent malignant degeneration. Thus, colorectal screening for polyps could be one of the most successful preventive interventions in medicine. Indeed, screening has been shown to reduce the incidence of CRC by more than 80% compared with a nonscreened population. 2,3 Despite this pathogenesis-based, theoretical superiority over screening programs for breast or prostate cancer, CRC remains a considerable cause of morbidity and mortality with CRC being the second most common malignancy. 4 The apparent discrepancy between theoretical potential and clinical reality points to the lack of an ideal modality for colorectal polyp screening. Currently, a number of tests are used to detect colorectal mass lesions: testing for occult blood in fecal material, 5,6 tumor markers, v,8 sigmoidoscopy, 9 singleor double-contrast barium enema] ~ and colonoscopy. 1~,12 None fulfill all essential requirements needed for a screening test13: high diagnostic accuracy, particularly with regard to the negativepredictive value, low cost, and high patient acceptance/compliance. The most widely used noninvasive screening method--fecal occult blood testing-has been shown to be neither sensitive nor specific. 5 Hence, most efforts have concentrated on morphologic screening methods. Reflecting its projectional nature, double-contrast barium enema (DCBE) is characterized by limited sensitivity in the detection of polyps. 14,15 Higher sensitivities have been achieved with colonoscopy, which in most centers has replaced barium enema as the modality of choice in the diagnostic evaluation of the colon.ll A major advantage of colonoscopy lies in its ability to biopsy and perform a polypectomy in the same