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Approximately 50% of patients with RRC will have metachronous metastatic disease at the time of diagnosis of pelvic recurrence [56]. CT examination of the chest, abdomen, and pelvis is the primary technique for identification of metastatic disease [43]. PET‐CT utilizing fluorodeoxyglucose (FDG) can occasionally be helpful in troubleshooting indeterminate lesions such as borderline enlarged para‐aortic or inguinal nodes or for detection of CT occult disease. Some centers routinely use PET‐CT for initial assessment of all patients with advanced pelvic tumors, as it can alter management by detection of multifocal metastases [57–59]. In one study, the use of PET in preoperative staging of patients with RRC was identified as an independent predictor of overall survival after R0 resection [60]. However, the evidence supporting routine use of PET‐CT for evaluation of recurrent colorectal cancer is limited [61–63]. A meta‐analysis of the role of PET in staging patients with recurrent colorectal cancer found a pooled sensitivity and specificity for detection of distant metastases of 91 and 83% respectively, and 97 and 98% for detection of liver metastases alone [64]. However, there was significant heterogeneity among included studies. Overall, the consensus in many centers, including the authors of this chapter, is that PET‐CT should be used selectively in the following circumstances: to troubleshoot indeterminate findings from conventional imaging such as scar versus tumor in the postoperative pelvis or for assessment of borderline enlarged lymph nodes; to help exclude CT occult metastatic disease (for example bony and brain metastases) in patients with extensive malignancy or where a tumor is associated with poor prognostic features; and when assessing response of metastatic disease to chemotherapy and/or radiotherapy.

For liver metastases, MRI is the most accurate and preferred modality and also provides useful anatomical information regarding suitability for radiofrequency ablation or excision [61].

For peritoneal metastases, the main role of imaging is assessment of the number, volume, and distribution of peritoneal disease and extraperitoneal metastases. The Peritoneal Cancer Index (PCI) is the most widely used method of estimating the tumor burden [65–71]. However, CT consistently underestimates PCI [72], with only 11% sensitivity for nodules smaller than 0.5 mm [73]. Overall accuracy of CT for detection of peritoneal lesions in the nine abdomino‐pelvic regions has been estimated at 51–88% [74]. MRI has been shown to correctly predict surgical PCI in 91% of patients [72] and diffusion‐weighted MRI has a sensitivity and specificity of 90 and 95.5% respectively for depicting peritoneal metastases in gynecological malignancy [75]. In the authors’ experience, most “CT and MRI occult” metastases measuring 5 mm diameter or more are retrospectively visible on scan review and there is considerable interobserver variability when reporting peritoneal metastases.