Efficacy of manual dissection of lymph nodes in colon cancer resections

The adequacy of lymph node dissection of colonic resection specimens influences the clinical and pathologic staging, leading to important postsurgical treatment decisions. Although manual lymph node dissection is the current standard at most institutions, recent statistical studies indicate that all lymph nodes, including those measuring 1-2 mm, should be recovered to be assured of lymph node negative status. Thus, we tested the efficacy of gross dissection by submitting the entire residual mesenteric fat. We analyzed 15 randomly chosen colonic resections (2 pT1, 1 pT2, 11 pT3, 1 pT4). After standard gross dissection of lymph nodes and submission of colonic material for diagnosis, the entire remaining mesenteric material was dehydrated over several days by serial washing in alcohol and acetone. All of the mesenteric tissue was submitted for histology. The average number of nodes found by original gross inspection was 20.8, while the average number of additional nodes found after clearing was 68.6. In all, 83% of the additional nodes were 2.0 mm or less in size. There were seven pNO cases; one was upstaged by additional findings that may have been artifactual. There were four pN1 cases; three were upstaged to pN2 after submission of the mesenteric material. All four pN2 tumors had additional metastases identified. In all, 75% of all positive nodes were under 2.0 mm in size. In this limited sample, standard gross dissection proved sufficient for most pNO tumors to remain node negative. However, our findings within the pN1 group show that examination of all of the mesenteric material may be necessary to be assured of correct pN status.