Figure 1
Assessment for lymph node metastasis is a critical component of staging for many tumor types. Historically, non-selective regional lymphadenectomy has been performed to ensure that all draining lymph nodes are removed. In humans, this technique results in extensive dissection and morbidity. In veterinary medicine, regional lymphadenectomy is not as extensive as in humans, and sampling focuses on a small number of easily accessible lymph nodes. Consequently, this approach can result in inadequate sampling if the draining lymph node is not within the sampled basin. Sentinel lymph node (SLN) mapping involves identification of the first draining lymph node(s) from a primary tumor to improve accuracy and decrease the extent of the surgical approach. Both pre and intraoperative methodologies are utilized to ensure all SLN(s) are sampled. The most commonly described SLN mapping techniques involve a combination of lymphoscintigraphy and blue dye. While these techniques are well established in the human literature, several limitations exist, which leads to investigation of other methodologies including contrast-enhanced ultrasound, radiographic lymphography, computed tomography lymphography (CTL), and intraoperative near-infrared fluorescence (NIR). Many SLN techniques are limited by cost, equipment and operator skill. Preoperative CTL has several advantages but may be less sensitive. Intraoperative NIR imaging agents have shown promise but may be less specific. A combination of several techniques helps to increase sensitivity of SLN identification but the correlation between the SLN and metastasis identification is not yet known in veterinary medicine.
In this lecture, Michelle Oblak will discuss the various SLN mapping techniques that have been described in surgical oncology and describe the current evidence available in veterinary medicine.