EUS evaluation up to the rectosigmoid angle for nodal staging in rectal cancer: Limitation of the technique

Introduction: According to the TNM classification, there are four levels of nodal involvement in rectal cancer (NO-N3). N0 demonstrates no lymph node involvement, N1 demonstrates the presence of involvement in <4 perirectal lymph nodes, N2 demonstrates the presence of involvement in >4 perirectal lymph nodes, and N3 demonstrates the presence of involvement in central lymph node (internal iliac vein nodes or inferior mesenteric vein nodes). Since the lymphatic spread of rectal cancer occurs in a contiguous fashion via nodes lying along the course of either the systemic circulation or the portal circulation, a comprehensive EUS evaluation of lymph node involvement would start in the area of the tumor and would continue until either benign nodes are documented to determine the presence of locoregional node disease (N0, N1 or N2) or until the involvement of central lymph nodes can be documented to determine the presence of advanced nodal disease (N3). The extent of EUS evaluation to achieve such complete nodal staging of rectal cancer (up to N3) has not been determined. Hypothesis: A complete lymph node staging of rectal cancer (including N3) can be accomplished by an EUS evaluation that extends up to the rectosigmoid angle. Methods: Patients with resectable rectal cancer were referred for preoperative staging by EUS. The EUS scope was inserted up to the level of the rectosigmoid angle (dome of the bladder) under ultrasound guidance. The extent of regional node involvement was mapped out by EUS. All EUS staging was compared to surgical pathology as the "gold standard" to evaluate the accuracy of the technique. Results: 20 patients with resectable rectal cancer were referred for preoperative EUS evaluation 15/20 had no nodal involvement by surgical pathology. 5/20 patients had documented nodal involvement by surgical pathology which included 2 with N1 disease, 1 with N2 disease, and 2 with N3 disease. By evaluating the lymphatic drainage up to the rectosigmoid angle (dome of the bladder), EUS accurately staged all N1 and N2 patients, but missed all of the N3 patients. Conclusions: EUS evaluation up to the rectosigmoid angle (dome of the bladder) is insufficient for complete nodal staging of patients with rectal cancer.