There are several points during the natural history of colorectal cancer when radiology can have an impact on the outcome. Radiologic techniques can be used in screening; establishing a diagnosis in symptomatic patients; presurgical staging; monitoring the effects of non-curative therapy; and surveillance after "curative" surgery. Of all of those roles, postoperative surveillance probably is the most contentious and the subject of this review.
The goal of postoperative surveillance is to identify asymptomatic recurrences in patients after curative surgery so that further treatment can be initiated and survival improved. The principal assumption is that the early detection of locally persistent tumor or metastases increases the likelihood of further treatment being curative. Consequently, the design of a surveillance strategy requires an effective means of identifying residual or recurrent disease and an effective treatment. This process can be aided greatly by understanding the biology of the disease. The key surveillance issues, from a radiologic perspective, are (a) whether patients should undergo postoperative surveillance at all; (b) whether imaging should play any part in a surveillance program and, if so, which imaging techniques should be employed and-how often; and (c) whether the postoperative surveillance should be universal or targeted. Inevitably, there is an economic consideration given the costs of investigations and the numbers of patients involved.