Although the absence of nodes at DWI is not a frequent finding, it appears to be a reliable predictor of yN0 status after CRT and may support the decision to consider organ-preservation treatment. Decreased lymph node size posttreatment is significantly associated with disease-free survival [103]. US Pelvis Transrectal A significant limitation of TRUS is the limited field of view that compromises assessment of relationship of the tumor, mesorectal tumor implants, tumor invasion in extramural vessels, and malignant nodes to the mesorectal fascia. In addition, TRUS is limited in its assessment of high rectal tumors and can only be used in nonstenotic patients. Local tumor staging in a direct comparison of TRUS to MRI in 34 patients, TRUS was accurate in tumor restaging after neoadjuvant CRT in 60% to 62% and high-resolution MRI in 68% [104,105], with a meta-analysis Staging of Colorectal Cancer demonstrating lower diagnostic accuracy than MRI post-CRT, and a statistically significant decline in T-stage accuracy compared with pre-CRT [106]. Sensitivity for complete response on TRUS is as low as 25% with a specificity of 94% [107]. Contrast-enhanced TRUS plus elastography was shown in one study to improve post-CRT local staging to 85% [108]. Detection of lymph node involvement with TRUS is limited to mesorectal nodes in the immediate vicinity of the tumor, which limits sensitivity. The sensitivity pretreatment ranges from 45% to 74% [63,64], and overall accuracy ranges from 62% to 83% [22], and this appears to be similar and even more variable posttreatment [105]. Post-CRT TRUS presents the same limitations of distance from the tumor as at baseline [104]. Variant 3: Colorectal cancer. Staging for distant metastases. Initial imaging. In this clinical scenario, a patient has been recently diagnosed with colon or rectal cancer and presents for evaluation of metastatic disease in the chest, abdomen, and pelvis.
Staging of Colorectal Cancer. Although the absence of nodes at DWI is not a frequent finding, it appears to be a reliable predictor of yN0 status after CRT and may support the decision to consider organ-preservation treatment. Decreased lymph node size posttreatment is significantly associated with disease-free survival [103]. US Pelvis Transrectal A significant limitation of TRUS is the limited field of view that compromises assessment of relationship of the tumor, mesorectal tumor implants, tumor invasion in extramural vessels, and malignant nodes to the mesorectal fascia. In addition, TRUS is limited in its assessment of high rectal tumors and can only be used in nonstenotic patients. Local tumor staging in a direct comparison of TRUS to MRI in 34 patients, TRUS was accurate in tumor restaging after neoadjuvant CRT in 60% to 62% and high-resolution MRI in 68% [104,105], with a meta-analysis Staging of Colorectal Cancer demonstrating lower diagnostic accuracy than MRI post-CRT, and a statistically significant decline in T-stage accuracy compared with pre-CRT [106]. Sensitivity for complete response on TRUS is as low as 25% with a specificity of 94% [107]. Contrast-enhanced TRUS plus elastography was shown in one study to improve post-CRT local staging to 85% [108]. Detection of lymph node involvement with TRUS is limited to mesorectal nodes in the immediate vicinity of the tumor, which limits sensitivity. The sensitivity pretreatment ranges from 45% to 74% [63,64], and overall accuracy ranges from 62% to 83% [22], and this appears to be similar and even more variable posttreatment [105]. Post-CRT TRUS presents the same limitations of distance from the tumor as at baseline [104]. Variant 3: Colorectal cancer. Staging for distant metastases. Initial imaging. In this clinical scenario, a patient has been recently diagnosed with colon or rectal cancer and presents for evaluation of metastatic disease in the chest, abdomen, and pelvis.