The American Society of Clinical Oncology developed in 1999 a set of guidelines for the surveillance of the post-operative patient with colorectal cancer after thorough review of the literature of common surveillance protocols. Protocols were reviewed on the basis of reduction in morbidity and five-year disease free survival. Monitoring carcino-embryonic antigen (CEA) levels and colonoscopy were found to be the most effective in many protocols, with liver function evaluation, fecal occult blood testing, liver ultrasound and chest X-ray being less effective in overall outcome (Desch et al. 1999). Colonoscopy appears to have the best predictive value for morbidity. A pre-operative or peri-operative evaluation of the entire colon is essential in the surveillance algorithm with a polyp free colon a must. Metachro-nous adenomas and neoplasms have been reported on surveillance colonoscopy at a fairly high rate (Fukutomi et al. 2002). Surveillance colonoscopy can be performed in three to five years if polyp free after surgery. However, colorectal surgeons surveyed stated they typically use a more frequent algorithm, such as 6-12 months intervals for the first 5 years.
The role of CT colonography has been evaluated specifically in this patient population. Incomplete colonoscopies secondary to post-operative strictures and rigid mesentery have been reported. In 2002, Gollub et al. reported a conventional colonoscopy failure rate of 4%-29% in post-operative or post-radiotherapy patients (Gollub et al. 2002). These patients would undergo a double contrast barium enema for complete evaluation of the colon. As discussed, CTC sensitivity for polyp detection is greater than DCBE and thus makes it a superior surveillance tool in this subset of patients.
The additional benefit of CTC for surveillance includes evaluation of the abdominal and pelvic viscera. The anastomosis can be specifically evaluated. In some surveillance algorithms, patients undergo colonoscopy and liver ultrasound. Laghi et al. reported on a group of patients undergoing surveillance with CEA, liver ultrasound, colonoscopy and chest X-ray (Laghi et al. 2003). In his study, the patients underwent contrast-enhanced CTC and findings were directly compared to conventional colonoscopy findings. CTC detected all polyps seen with conventional colonoscopy with two false positives. The study was also able to diagnose liver metastases and basal lung nodules. Therefore, contrast-enhanced CTC appears to be a valuable alternative surveillance tool in post-operative patients at increased risk for adenomas and cancer.
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