With accuracies for T staging varying between 69% and 97%, endorectal ultrasonography (US) is currently the most selleck chem ARQ197 accurate imaging modality for the assessment of T1 tumors[2]. ERUS and endorectal MRI have similar accuracy in the differentiation between superficial (T1 and T2) and T3 tumors[26]. However, endorectal MRI is related to high costs, limited availability and is less patient friendly. Consequently, endorectal MRI is not recommended by the European Society for Medical Oncology Guidelines as a preferred imaging modality for clinical T stage in colorectal cancer[22]. METASTATIC SPREADING OF CRC In 25% of patients with colonic cancer and in 18% of patients with rectal cancer, metastases are present at the time of the first diagnosis.
The most frequently used imaging modalities for the detection of CRC metastases are US, CT, MRI and PET/CT[27]. Current National Comprehensive Cancer Network guidelines for initial staging of CRC suggest the use of chest/abdomen/pelvis CT or MRI, while FDG-PET/CT is reserved for surveillance or problem solving. N staging ERUS, CT and MRI use the size as the main criterion in the assessment of nodal involvement, although the lymph node size is not an ideal indicator of metastasis and lacks sufficient accuracy for clinical decision-making[28]. FDG-PET gives better insight in tumor biology, however, due to limited spatial resolution it does not allow for reliable detection of small lymph node metastases. FDG-PET/CT may provide additional information and could increase the accuracy of lymph node involvement significantly with a sensitivity and specificity of 51% and 85% for local lymph nodes and 62% and 92%, for distant lymph nodes[29].
M staging Correct detection of hepatic and pulmonary metastases can be challenging considering the possible difficulties in differentiation with benign lesions in these organs. CT has a better diagnostic performance (sensitivity 74%-84%, specificity 95%-96%) compared to US in detection of CRC liver metastases[30]. A meta analysis of prospective studies comparing FDG-PET, MRI, and CT demonstrated a superior performance of MRI over the other two modalities on a lesion-by-lesion basis of the liver and in particular in evaluating lesions less than 1 cm in size (sensitivity 80%-88% and specificity 93%-97%)[6].
Recently, DWI and hepatobiliary phase MRI with new hepatobiliary contrast agents have been integrated for the detection of liver metastases demonstrating improved sensitivity over routine MRI alone[31]. The newest hepatobiliary contrast agent available is Gd-EOB Primovist? in Europe and Eovist? in United States and Canada (Bayer Healthcare, Leverkusen, Germany). Uptake of contrast GSK-3 within the hepatocytes results in peak parenchymal enhancement approximately 10-20 min p.i., referred to as the hepatobiliary phase.