Minimally invasive sentinel lymph node mapping of the pig colon with Lymphoseek.

Background: Minimally invasive surgery and sentinel node mapping are being utilized increasingly in colon cancer surgery. Making these techniques efficient and easy to perform will be essential for the future of this and other gastrointestinal operations. The purpose of this study was to test a new laparoscopic gamma detection probe for minimally invasive sentinel node mapping of the colon, while utilizing Lymphoseek, a radiopharmaceutical specifically designed for sentinel lymph node (SLN) detection.

Methods: Eight anesthetized pigs received an endoscopic co-injection of Lymphoseek and Isosulfan Blue in the colon. The laparoscopic gamma detector, inserted via a 12-mm trocar, was used to identify radioactive sentinel lymph nodes. The reliability of the side-viewing probe was tested using a radioactive source. All blue and radioactive lymph nodes were excised and the signal-to-background ratio (S/B) and percent of injected dose (%ID) were measured.

Results: The probe was easy to maneuver and led to efficient visualization of the radioactive node. The side port allowed for better distinction between injection site scatter and sentinel node activity. The reliability of the probe was validated by an identification rate of 97%. At least one SLN was detected for each pig; two SLNs were detected in two pigs. All SLNs were stained blue. The SLN S/B ranged from 38 to 315 and the %ID ranged from 0.06% to 2.01%. Sentinel nodes were found within 10 minutes.

Conclusions: Minimally invasive sentinel node mapping with the radiopharmaceutical Lymphoseek and a side-viewing gamma detector yielded high S/B and directionality for accurate mapping of gastrointestinal sentinel lymph nodes within minutes of radiotracer administration.