Role of preoperative local and distant staging in rectal cancer.

Preoperative imaging in rectal cancer is very important, as accurate staging determines optimal treatment strategy. In this review, imaging modalities for locoregional and distant staging in rectal cancer are discussed. For local staging, superficial tumors are best staged using endorectal US (EUS), as EUS is the most accurate modality for assessment of tumor ingrowth into the rectal wall layers. The more advanced tumors are best imaged using MRI, because MRI accurately predicts the distance from tumor to mesorectal fascia, and thus the circumferential resection margin (CRM), as well as possible invasion into surrounding organs. For the prediction of the nodal status none of the three imaging modalities - EUS, MRI and CT - can be reliably used for clinical decision-making. Only MRI using lymph node specific contrast (such as ultrasmall paramagnetic iron oxide-enhanced MRI) seems promising for the detection of nodal disease. For the detection of distant metastases transabdominal ultrasound and chest X-ray are used as a primary screening tool. However, for the high prevalence group (stage III) both methods are insufficiently sensitive, and CT of the chest plus abdomen is preferred.