[Contribution of nuclear medicine to lymphatic mapping and sentinel node identification in oncology]

An overview of the current applications of nuclear medicine for lymphatic mapping and sentinel node identification is given. The validation of the sentinel node concept in oncology has led to the rediscovery of lymphoscintigraphy. By combining preoperative lymphatic mapping with intraoperative gamma probe detection this nuclear medicine procedure is increasingly used to identify and detect the sentinel node in melanoma, breast cancer, and in other malignancies such as penile cancer and vulvar cancer. In melanoma, the adequate combination of dynamic and static gamma camera images enables lymph node visualization with identification of the sentinel node in more than 97% of the cases. The variability in drainage in areas such as trunk, head and neck makes lymphoscintigraphy indispensable in protocols of sentinel node biopsy. The reproducibility of lymphoscintigraphy for sentinel node detection varies from 85% to 88% and the method appears to have a high interobserver agreement. In contrast to the procedure of lymphoscintigraphy for melanoma, for which the only dilemma remaining is probably the choice of the tracer, in breast cancer there has not yet been reached a consensus for many topics such as tracer characteristics, injection volume, and principally the site of administration. Lymphoscintigraphy by subdermal tracer administration is able to detect axillary lymph nodes in 98% of the cases but the method is accompanied by a low visualization incidence (2%) of drainage outside the lower axilla such as the internal mammary chain. This latter aspect appears to occur in 16% to 35% in the series using peri- or intratumoural administration with an axillary rate of visualization of 75% to 98%. Although peritumoural administration is predominantly associated with late lymph node detection, the early appearance observed after subdermal and intratumoural tracer injection justifies the obtention of early gamma camera images. The strategies of identification of the sentinel node depend strongly on the results of lymphoscintigraphy. In melanoma, the rapid lymphatic drainage and the visualization of afferent lymphatic vessels enables sentinel node identification by lymphoscintigraphy in almost the totality of the cases and intraoperative probe detection may subsequently be performed. In breast cancer, the slower drainage pattern may hamper image interpretation and diagnostic conclusion. Considering the first appearing node and the visualization of an afferent lymphatic vessel as the major criteria to identify the sentinel node, scintigraphy may be considered conclusive in approximately 75% of the cases, and not conclusive in about a fourth part of the cases in which 2 or more lymph nodes appear simultaneously without lymph vessel delineation. When lymphoscintigraphy is not conclusive, additional lymphatic mapping with blue dye is recommended to definitively identify the sentinel node. The use of nuclear medicine techniques for the sentinel node procedure will become an important part of clinical work in the nuclear medicine and surgical oncology practice of the next years. Principally mammary lymphoscintigraphy demands from the nuclear medicine community and allied disciplines a prompt standardization of the technique to solving some controversial aspects such as tracer requirements, administration route and interpretation criteria.