PET/CT is useful for determining overall stage and identifying patients with metastatic disease (sensitivity of 89% and specificity of 64%); however, the accuracy on a lesion-by-lesion basis is relatively low compared with contrast- enhanced CT and MRI for liver metastases (55% versus 89% in a study comparing PET/CT to MDCT) [128,129]. PET/CT may help to exclude other sites of disease beyond the liver or, in complex cases, to improve staging accuracy in which it has been shown to result in a change in management in up to 8% to 11% of patients [128,130- 132]. Caution should be exercised, however, as the findings of PET/CT may be nonspecific and could result in a negative impact on patient care in up to 9% of patients [128]. Additionally, PET/CT has further reduced sensitivity Staging of Colorectal Cancer for lesions in the setting of neoadjuvant therapy and should be used in conjunction with IV contrast CT or MRI for presurgical planning of liver metastases [133]. PET/CT may add influence in the positive predictive value of avid lymph nodes because it has a higher specificity than other modalities. The sensitivity of detecting nodal metastases is only 43% with a specificity of 80%, and again size is not a helpful characteristic. Because of limited sensitivity of MRI for lung nodules, a chest CT can be utilized in addition to abdominal MRI for complete staging. The National Comprehensive Cancer Network recommends that patients with newly diagnosed colorectal cancer undergo staging chest CT, because staging chest CT has been shown to detect more lung metastases than chest radiography [119]. In a series of 74 patients with newly diagnosed rectal cancer who underwent both chest CT and chest radiography, 37% of patients with a normal chest radiograph had a lesion visible only on the chest CT, and 17% of these patients were found to have at least one pulmonary metastasis [119].
Staging of Colorectal Cancer. PET/CT is useful for determining overall stage and identifying patients with metastatic disease (sensitivity of 89% and specificity of 64%); however, the accuracy on a lesion-by-lesion basis is relatively low compared with contrast- enhanced CT and MRI for liver metastases (55% versus 89% in a study comparing PET/CT to MDCT) [128,129]. PET/CT may help to exclude other sites of disease beyond the liver or, in complex cases, to improve staging accuracy in which it has been shown to result in a change in management in up to 8% to 11% of patients [128,130- 132]. Caution should be exercised, however, as the findings of PET/CT may be nonspecific and could result in a negative impact on patient care in up to 9% of patients [128]. Additionally, PET/CT has further reduced sensitivity Staging of Colorectal Cancer for lesions in the setting of neoadjuvant therapy and should be used in conjunction with IV contrast CT or MRI for presurgical planning of liver metastases [133]. PET/CT may add influence in the positive predictive value of avid lymph nodes because it has a higher specificity than other modalities. The sensitivity of detecting nodal metastases is only 43% with a specificity of 80%, and again size is not a helpful characteristic. Because of limited sensitivity of MRI for lung nodules, a chest CT can be utilized in addition to abdominal MRI for complete staging. The National Comprehensive Cancer Network recommends that patients with newly diagnosed colorectal cancer undergo staging chest CT, because staging chest CT has been shown to detect more lung metastases than chest radiography [119]. In a series of 74 patients with newly diagnosed rectal cancer who underwent both chest CT and chest radiography, 37% of patients with a normal chest radiograph had a lesion visible only on the chest CT, and 17% of these patients were found to have at least one pulmonary metastasis [119].