Study objectives: Although the sentinel lymph node (SLN) concept has traditionally been applied to solid organs, we hypothesized that the pleural space might drain into a specific SLN group. The identification of such a nodal group could assist in the staging and treatment of pleural-based diseases, such as mesothelioma, or other lung cancers with visceral pleural invasion. The purpose of this study was to determine whether the pleural space has an SLN group.
Design: Sixteen rats underwent right or left pleural space injection of a novel lymph tracer, quantum dots (QDs), which have a hydrodynamic diameter of 15 nm and fluoresce in the near-infrared (NIR) spectrum. Nodal uptake of the entire thorax was imaged with a custom system that simultaneously acquired color video, NIR fluorescence of the QDs, and a merged picture of the two in real-time. Six pigs underwent right or left pleural space injection of QDs and similar imaging.
Measurements and results: In the rat, the QDs drained solely to the highest superior mediastinal lymph node group, corresponding to lymph node station 1, according the regional lymph node classification for lung of the American Joint Committee on Cancer. In one rat, the injection of QDs in the left pleural space resulted in migration to the contralateral station 1 lymph node group. The injection of QDs in the right or left pleural space of the pig resulted in migration solely to the ipsilateral highest superior mediastinal lymph node group.
Conclusions: NIR fluorescence imaging in two species demonstrated that the highest superior mediastinal lymph nodes of station 1 are the SLNs of the pleural space. This study also provides intraoperative feasibility and proof of the concept for identifying lymph nodes communicating with the pleural space on a patient-specific basis, in real-time, and with high sensitivity.