Ann Thorac Surg 2004;77:1037-1038
© 2004 The Society of Thoracic Surgeons
Original articles: general thoracic
Invited commentary
John A Odell, MD
Division of Cardiovascular and Thoracic Surgery, Mayo Clinic Jacksonville, 4500 San Pablo Rd, Jacksonville, FL 32224 , USA
e-mail: odell.john{at}mayo.edu
The authors have taken an opposite tack to the usual method of defining lymph nodes on computed tomography (CT). They have instead used a contrast agent to delineate the draining lymph nodes of presumed lung cancer, rather than silhouetting the nodes against the contrasted vascular tree of the lung and mediastinum. The depiction is a CT one and requires careful timing with the maximal attenuation occurring one minute after injection into the peripheral lung nodule. The study is helpful in that the surgeon may be directed to the site of lymph nodes, but does not indicate whether the lymph node is involved by cancer or not. In fact, in this series, there were no nodes involved by metastatic cancer.
Will the procedure result in directed excision or biopsy rather than lymph node sampling or excision of all mediastinal and hilar lymph nodes? This question is difficult to answer. At present, it is uncertain if the sentinel node hypothesis is valid in lung cancer. The authors have hypothesized that analysis of the time course of dynamic CT images with adequate fractionated intervals could identify the first draining lymph node. The disadvantage of the technique is that although careful analysis of the preoperative CT may guide the surgeon by "improved visualization", it does not take into account intraoperative factors including anatomy or skill of the surgeon, which may result in the node not being analyzed. In contradistinction to other techniques [1, 2], it does not mark or intraoperatively enhance the node so that it is more easily found.
The procedure appears to be demanding with respect to timing and labor intensive with respect to analysis. It is possible that with further study these issues may be refined. In contrast to the Swensen technique of measuring attenuation[3], attenuation is measured after contrast enhancement. In this study, the time taken for a steady state to occur is not stated, but presumably this is short. No complications were documented, but potential complications are discussed and predictably will occur as more cases are done.
Does the study offer potential? It may lead to a better understanding of lymph node drainage in lung cancer. Previously, knowledge of lymph node drainage of lung segments or lobes has been the result of pathological correlation of lesion and involved node. The presumption is that if nodes are consistently involved then drainage patterns have been demonstrated. It is quite possible that if this study is continued with or pursued more widely, that a different or better understanding of lung lymphatics will take place. Other questions can be posed. What happens when tumor cells occlude lymphatics? Will alternative channels be present? Will lymph node attenuation occur in these circumstances? Will attenuation be delayed in the presence of obstructed lymphatics? Does intravenous contrast need to be given? Is localization of lymph nodes using this technique better than traditional methods?
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- Sugi K., Fukuda M., Nakamura H., Kaneda Y. Comparison of three tracers for detecting sentinel lymph nodes in patients with clinical N0 lung cancer. Lung Cancer 2003;39:37-40.[Medline]
- Nakagawa T., Minamiya Y., Katayose Y., et al. A novel method for sentinel lymph node mapping using magnetite in patients with non-small cell lung cancer. J Thorac Cardiovasc Surg 2003;126:563-567.[Abstract/Free Full Text]
- Swensen S.J., Viggiano R.W., Midthun D.E., et al. Lung nodule enhancement at CT: multicenter study. Radiology 2000;214:73-80.[Abstract/Free Full Text]
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