Radiologic imaging modalities in the diagnosis and management of colorectal cancer

Colorectal carcinoma poses a serious public health threat. Detection in its early stages is the best predictor for long-term survival, which is the impetus for population-based screening programs. We believe that full-colon imaging by either DCBE or colonoscopy is necessary for colon cancer screening because flexible sigmoidoscopy, even if perfect, only detects 50% to 60% of colon cancers, a rate far worse than even the worst rate reported for single-contrast barium enema. Screening for colon cancer with flexible sigmoidoscopy is equivalent to performing a "left" mammogram for the detection of breast cancer. The role of CT colonography is still to be determined. When confronted with a symptomatic patient, barium enema is applied in conjunction with CT to detect primary colorectal carcinoma, to differentiate it from other benign and malignant processes involving the colon, and to assess for disease extent before surgery in selected high-risk patient populations. Pelvic MRI may be useful in the preoperative assessment of patients with rectal carcinoma as a means for assisting surgical planning. CT, MRI, and barium enema are used in postoperative follow-up for detecting local recurrence and distant spread. In response to known difficulty in discriminating between normal postoperative changes and tumor recurrence and in determining the nature of certain liver lesions, FDG-PET has been approved for the detection and localization of recurrent colorectal cancer in patients with rising CEA levels and indeterminate findings on standard imaging studies. Given its current promise of offering high sensitivity, specificity, and accuracy, the indications for PET may well expand in the future, but its final role is still to be determined.