Preclinical study of peripheral parenchymal lymphatic drainage in lung.

Background: This study aims to determine the regularity of sentinel lymph nodes of peripheral lung parenchyma and the lymphatic drainage between adjacent pulmonary segments in experimental animals. Methods: Thoracotomy was performed on 12 experimental Guizhou miniature pigs, and 1 mL methylene blue was injected into the superior segment of the lower lobe (S6) and the anterior segment of the upper lobe (S3), successively, to observe lymphatic drainage, in sentinel lymph nodes and the lymphatic drainage between adjacent segments. Results: A total of 161 lymphatic vessels were observed in 48 pulmonary segments, with an average of 3.4 lymphatic vessels per segment: RS6 (superficial 1.0±0.61, deep 2.5±1.00), RS3 (superficial 1.0±0.51, deep 2.0±1.07), LS6 (superficial 3.0±0.42, deep 1.0±0.38), LS3 (superficial 1.0±0.43, deep 2.0±0.62). There were significantly more lymphatic vessels in deep plexus than in superficial (p<0.01). As for sentinel lymph nodes, LS6 drained to the hilar, subcarinal and 4L lymph nodes; RS6 drained to the hilar and subcarinal lymph nodes; LS3 drained to the hilar and 4L lymph nodes; and RS3 drained to the hilar and 4R lymph nodes. In addition, methylene blue could drain from peripheral lung tissue of S3 and S6 directly to mediastinal lymph nodes through superficial plexuses. Lymphatic drainage regularity of S3 and S6 to adjacent pulmonary segments were also observed. The R6 rarely drained to the basal segment, while R3 could possibly drain to the posterior segment. Conclusion: The regularity of peripheral pulmonary parenchymal lymphatic drainage in experimental animals can provide a basis for the management of lymph nodes in pulmonary segmentectomy in humans, to a certain extent.