In vivo mapping of pulmonary lymphatic pathways: A new technique

Recently we reported on a simple method of tracing the regional lymphatic drainage of the tracheobronchial tree using radiocolloids in patients undergoing bronchoscopy. The specificity and accuracy of the technique were evaluated in a series of canine experiments. Using a rigid bronchoscope and a long injecting needle, a mixture of 0.5 cc of radioactive colloid (200 μCi ¹⁹⁸Au, 2 mCi ^99mTc sulfur colloid, or 2 mCi ^99mTc antimony sulfide), and 0.5 cc of a colored colloidal marker (trypan blue) was injected submucosally in selected bronchial regions in a series of five dogs. Four hours after injection the distribution of the injected radioactivity was demonstrated by scanning with a gamma camera. The animals were killed and autopsies performed. Thoracic lymph node dissections showed the distribution of the colored colloidal marker. This was compared with the radioactivity of the lymph nodes which had been excised and counted in vitro with a scintillation counter. The radioactivity of histologically proven lymphatic tissue was compared with that of adjacent nonlymphatic tissue. The study showed that 95% of the most radioactive lymph nodes found on scintillation counting were visualized on scanning with the gamma camera. On the other hand, in the early part of the study, not all radioactivity visualized with the gamma camera could be accounted for on scintillation counting of excised lymph nodes. With technical refinement in the latter experiments lymph nodes were found to account for 100% of the images found on scanning. On histological examination the radioactivity was found to be concentrated in lymphatic tissue. This study demonstrates that: (1) Radioactive spread following injection is located in the lymph nodes, (2) In vitro mapping of primary lymphatic drainage patterns of regional bronchi is feasible, and (3) Lymph node patterns visualized on scanning may help in surgical lymph node dissections.