Current imaging strategies for colorectal cancer.

Endoscopy and barium enema examinations are used to identify the primary site of disease in patients with clinical suspicion of colorectal cancer. Once colorectal cancer has been confirmed by imaging studies and biopsy, preoperative evaluation is directed toward accurate disease staging. Most currently available imaging techniques are inaccurate for detecting transmural extension, perienteric spread of tumors and distant lymph node involvement. Although both computed tomography (CT) and magnetic resonance imaging (MRI) have an unacceptably low sensitivity for accurate staging, CT is clearly superior to MRI for detecting extrahepatic metastases. Transrectal ultrasonography, however, is a promising new method for detecting perirectal spread of disease. The diagnostic efficacy of MRI and intravenous dynamic hepatic CT for detecting liver metastases is approximately equal. CT during arterial portography is recommended before resection of solitary liver metastases. Chest radiography is also part of the routine preoperative evaluation. Bone scans are rarely performed in patients without the skeletal pain suggestive of bone metastases. During the years following surgery for colorectal cancer, many patients undergo special imaging studies to identify local tumor recurrence, secondary tumor growth elsewhere within the large bowel and both regional and distant spread of disease. Thus, for the patient with a sharply increasing carcinoembryonic antigen level, CT of the abdomen and liver is the current recommendation. Immunoscintigraphy is a new imaging modality that addresses some of the limitations of current diagnostic procedures for colorectal cancer. This procedure gives whole body information on disease extent, especially in the extrahepatic abdomen and pelvis, and can therefore contribute to patient management decisions.