Rectal cancer: CT local staging with histopathologic correlation

Background: Many surgical options, eventually combined with neoadjuvant therapy, are available for the treatment of rectal cancer. Preoperative staging is essential to plan the correct treatment. Our aim was to evaluate the diagnostic accuracy of computed tomography (CT) in the local staging of rectal cancer. Methods: Between February 1995 and May 2000, 105 patients (65 male, 40 female; mean age = 58, range = 36-88 years) after preoperative locoregional CT staging underwent rectal resection for rectal cancer. In all patients, radiologic T and N staging was verified with pathologic examination of excised specimens. Patients were examined after air insufflation of the ampulla, during intravenous contrast injection; analysis of the rectoanal region was performed with thin (3-5 mm) contiguous slices. For T staging, Tis-T2, T3, and T4 groups were considered. For N staging, two groups of patients were considered: in 52 patients, N+ stage was attributed to all visible lymph nodes; in the other 53 patients, only lymph nodes >5 mm were recorded as N+. Results: Pathologic examination showed 61 T1-T2, 40 T3, and four T4 tumors; CT examination correctly identified 50 T1-T2 (81.9%), 33 T3 (82.5%), and three T4 (75%) lesions. With regard to N stage, pathologic examination in the first group (52 patients) showed only 11 cases of lymph node involvement. CT examination detected all 11 true-positive lymph nodes but overestimated 30 false-positive cases. In the second group (53 patients), pathology showed 26 cases of nodal involvement: CT examination identified 23 true-positive, 19 true-negative, eight false-positive, and three false-negative lymph nodes. Conclusion: CT correctly staged 86 (82%) of 105 lesions. Overestimation occurred in T2 patients (11 of 61, 18%) and underestimation in T3 patients (seven of 33, 21%), in accordance with other reports dealing with superior accuracy of endorectal ultrasonography in local staging of early disease. Conversely, the criterion we suggest for evaluating metastatic perirectal lymph nodes (diameter > 5 mm) provided 79.2% diagnostic accuracy, 88.5% sensitivity, and 86.5% negative predictive value. This can be useful in those patients in whom prompt surgery, soon after radiochemotherapy in the case of nodal involvement, may likely be curative. With further improvement with spiral CT in local staging and nodal involvement, a larger number of transanal curative resections can be predicted.