Ex vivo sentinel node mapping in carcinoma of the colon and rectum

Increasing evidence supports that the sentinel node (SN) is at greatest risk for harboring metastatic disease. This study describes a novel technique to identify the SN in colorectal carcinoma.

Within 30 minutes of resection, colorectal specimens were injected submucosally with isosulfan blue in four quadrants. Blue lymphatic channels were identified in the mesentery and followed to the blue-stained SN(s), which were then harvested. The specimen was fixed in formalin and subsequently analyzed in the usual fashion. Blue-stained nodes that were negative by hematoxylin and eosin staining were further analyzed by immunohistochemical staining.

During a 6-month period, 26 patients with adenocarcinoma of the colon and rectum undergoing routine resection were studied. There were 18 men and 8 women ranging in age from 29 to 86 years (median 66). Blue-stained SNs were identified in 24 of 26 specimens. The mean number of SNs identified per patient was 2.8 +/- 1.6. Seventy-three SNs were identified from a total of 479 lymph nodes harvested. The mean number of nodes identified per patient was 18.4 +/-7. A total of 67 lymph nodes in 12 patients were identified by hematoxylin and eosin staining to have evidence of metastatic disease. Fourteen (20%) of these nodes in six patients were stained blue. However, with immunohistochemical staining, only one blue node did not have evidence of metastatic tumor in a lymphatic basin with tumor present. Four patients (29%) whose lymphatic basins were negative by hematoxylin and eosin staining were upstaged by immunohistochemical staining of the SN.

Ex vivo mapping of the colon and rectum is technically feasible and may provide a useful approach to the ultrastaging of colorectal carcinoma.