Pathologic evaluation of sentinel lymph nodes in colorectal carcinoma

Background.-The identification of lymph node metastases in colorectal resec tion specimens is necessary for accurate tumor staging. However, routine ly mph node dissection by the pathologist yields only a subset of nodes remove d surgically and may not include those nodes most directly in the path of l ymphatic drainage from the tumor. Intraoperative mapping df such sentinel l ymph nodes (SLNs) has been reported in cases of melanoma and breast cancer. We applied a similar method to cases of colorectal carcinoma, with emphasi s on the pathology of the SLNs. Methods.-Eighty-three consecutive patients with colorectal carcinoma were e valuated after intraoperative injection of 1 to 2 mL of 1% isosulfan blue d ye (Lymphazurin) into the peritumoral subserosa. Blue-stained lymph nodes w ere suture-tagged by the surgeon within minutes of the injection for identi fication by the pathologist, and a standard resection was-performed. Design ated SLNs were sectioned at 10 levels through the block; a cytokeratin immu nostain (AE1) was also obtained. To evaluate the possibility that increased detection of metastases in the SLN might be solely due to increased histol ogic sampling, all initially negative non-SLNs in the first 25 cases were s ectioned also at 10 levels. Results.-Sentinel lymph nodes were identified intraoperatively in 82 (99%) of 83 patients and accounted for 152 (11.9%) of 1275 lymph nodes recovered, with an average of 1.9 SLNs per patient. A total of 99 positive lymph node s (38 positive SLNs and 61 positive non-SLNs) were identified in 34 node-po sitive patients. The SLNs were the only site of metastasis in 17 patients ( 50%); while 14 patients (41%) had both positive SLNs and non-SLNs. Three pa tients (9%) had positive non-SLNs with negative SLNs, representing sk;ip me tastases. In patients with positive SLNs, 91 (19%) of 474 total lymph nodes and 53 (12%) of 436 non-SLNs were positive for metastasis. In patients wit h negative SLNs, 8 (1%) of 801 total lymph nodes and 8 (1.2%) of 687 non-SL Ns were positive for metastasis. Multilevel sections of 330 initially negat ive non-SLNs in the first 25 patients yielded only 2 additional positive no des (0.6%). All patients with positive SLNs were correctly staged by a comb ination of 4 representative levels through the SLN(s) together with a singl e cytokeratin immunostain. Conclusions.-Intraoperative mapping of SLNs in colorectal carcinoma identif ies lymph nodes likely to contain metastases. Focused pathologic evaluation of the 1 to 4 SLNs so identified can improve the accuracy of pathologic st aging.