Special Imaging Considerations In rectal tumors, because of the need for high-resolution anatomic detail in determining local tumor extension, the local staging of the tumor is often considered separately from the evaluation of distant metastatic disease, resulting in the need for a combination of modalities to fully stage the patient. In contrast, locoregional staging by imaging is not an issue for colon (nonrectal) cancers, and thus only the evaluation of distant metastatic disease is required. OR Discussion of Procedures by Variant Variant 1: Rectal cancer. Locoregional staging. Initial imaging. In this clinical scenario, a patient has been recently diagnosed with rectal cancer and presents for evaluation of local regional extent of the rectal cancer to determine if the person would benefit from neoadjuvant therapy before possible surgical resection. This variant excludes (nonrectal) colon cancers. For lymph node involvement, CT remains relatively nonspecific for N-stage determination. There is little agreement on the critical cut-off diameter to determine if lymph nodes are involved in the disease process. One study suggests 4.5 mm; however, nodal size is not seen as a predictor of nodal status at surgery [8,23]. Because detection of nodes involved with tumor remains a difficult problem, if a colonic resection is planned, local node groups should be encompassed in a properly performed cancer operation. Accuracies for CT detection of lymph node stage range from 56% to 84% [19,20,24-26]. Locoregional staging is not routinely performed for colon cancer; however, CT is Staging of Colorectal Cancer still useful in the initial evaluation of all patients scheduled for colorectal carcinoma surgery because of its ability to obtain a rapid global evaluation and demonstrate potential complications of the tumor (eg, perforation, obstruction) that may not be clinically apparent [18].
Staging of Colorectal Cancer. Special Imaging Considerations In rectal tumors, because of the need for high-resolution anatomic detail in determining local tumor extension, the local staging of the tumor is often considered separately from the evaluation of distant metastatic disease, resulting in the need for a combination of modalities to fully stage the patient. In contrast, locoregional staging by imaging is not an issue for colon (nonrectal) cancers, and thus only the evaluation of distant metastatic disease is required. OR Discussion of Procedures by Variant Variant 1: Rectal cancer. Locoregional staging. Initial imaging. In this clinical scenario, a patient has been recently diagnosed with rectal cancer and presents for evaluation of local regional extent of the rectal cancer to determine if the person would benefit from neoadjuvant therapy before possible surgical resection. This variant excludes (nonrectal) colon cancers. For lymph node involvement, CT remains relatively nonspecific for N-stage determination. There is little agreement on the critical cut-off diameter to determine if lymph nodes are involved in the disease process. One study suggests 4.5 mm; however, nodal size is not seen as a predictor of nodal status at surgery [8,23]. Because detection of nodes involved with tumor remains a difficult problem, if a colonic resection is planned, local node groups should be encompassed in a properly performed cancer operation. Accuracies for CT detection of lymph node stage range from 56% to 84% [19,20,24-26]. Locoregional staging is not routinely performed for colon cancer; however, CT is Staging of Colorectal Cancer still useful in the initial evaluation of all patients scheduled for colorectal carcinoma surgery because of its ability to obtain a rapid global evaluation and demonstrate potential complications of the tumor (eg, perforation, obstruction) that may not be clinically apparent [18].