Pulmonary lymphatic fluid predominately flows along the bronchi. However, there are reports suggesting that an alternative lymphatic pathway exist, which may result in skip metastases. The aim of this study was to evaluate the subpleural lymph flow in vivo using indocyanine green (ICG) fluorescence.
One hundred cases were enrolled. ICG was injected into the macroscopically healthy subpleural space. Intraoperative fluorescence images were then observed in real time.
ICG fluorescence was observed moving through subpleural channels in 58/100 cases. ICG flowed into adjacent lobes over interlobar lines in 18 cases and flowed from the visceral pleura directly into the mediastinum in 5 cases. The frequency of mediastinal detection without hilar lymph node detection was significantly higher in the left lung compared to the right (p < 0.05). The subpleural lymph flow detection rates were significantly lower in patients with smoking pack-years ≥ 40 than those with < 40 (p < 0.05).
The flow of lymphatic fluid directly into the mediastinum suggests one mechanism of skip metastasis. In addition, the reduction of the subpleural lymph flows in smokers with ≥ 40 pack-years suggests that smoking might modify lymph flow patterns. These findings may assist in selecting the optimal therapy for patients with possible skip metastasis.
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The authors would like to express their gratitude to Dr. Robert Qaqish and Ms. Cara Summers from University Health Network, Toronto, Canada, for their English editing.
Conflict of interest
All authors declare that they have no conflict of interest.
Electronic supplementary material
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Video 1. (a) The ICG flowed through the subpleural space forming obvious tracts, but stayed within the injected lobes (arrows). (b) The ICG flowed through the subpleural space to adjacent lobes over the interlobar lines (arrow). (c) The ICG flowed through the subpleural space directly into hilar LNs (arrow). (d) The ICG flowed through the subpleural space directly to the mediastinum (arrow). Abbreviations: UL: upper lobe, LL: lower lobe, PN: phrenic nerve, dAO: descending aorta, PA: pulmonary artery, AA: aortic arch (MP4 7265 KB)
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Takeda, A.H., Watanabe, Y., Nagata, T. et al. Detection of alternative subpleural lymph flow pathways using indocyanine green fluorescence. Surg Today 48, 640–648 (2018). https://doi.org/10.1007/s00595-018-1631-1
- Subpleural lymph flow
- Indocyanine green fluorescence
- Lung cancer
- Skip metastasis
- Lung remodeling