Improving lymph node yield in retroperitoneal lymph node dissection using fluorescent molecular imaging: a novel method of localizing lymph nodes in Guinea pig model

Objectives: To propose that fluorescent molecular imaging has utility in specifically identifying the lymph nodes, thereby enabling more definitive lymph node visualization and dissection. Retroperitoneal lymph node dissection (RPLND) is an invasive procedure with significant morbidity. A minimally invasive approach would be of great clinical benefit but has been limited by the extensive perivascular dissection required to remove all lymphatic tissue. Directed lymph node visualization would allow a limited dissection, making a laparoscopic approach more feasible.

Methods: Ten male Hartley guinea pigs underwent nonsurvival RPLND, 5 with the protease activatable in vivo fluorescent molecular imaging agent, ProSense and 5 without image guidance (control). ProSense was administered 24 hours before surgery and detected 24 hours later using a photodynamic detector. In group 1, RPLND was first performed without molecular imaging followed by image-guided lymph node dissection for residual nodes. In group 2, the near infrared detector was used initially for lymph node excision followed by traditionally unassisted extraction of the residual lymph nodes. The lymph nodes were extracted, counted, and sent for histopathologic analysis.

Results: With the assistance of molecular imaging, no additional lymph nodes were identified after complete dissection, and all tissue identified by ProSense was confirmed by histopathologic analysis to be lymph nodes. Without molecular imaging, all lymph nodes were not identified, and in 2 instances, the tissue was incorrectly thought to be lymphatic tissue.

Conclusions: Molecular image-guided RPLND is a promising technique to improve in vivo, live visualization and dissection of lymph nodes and has the potential for application in improving the diagnosis and treatment of other urologic malignancies.