Recent studies have demonstrated that removal of lymph nodes can affect long-term outcomes and survival, especially for patients with mast cell tumors. Since mass excision procedures for skin malignancies are frequently performed in primary care veterinary practice, it is important for clinicians to know how to identify the appropriate lymph node(s) to remove. Focusing on techniques that are easily accessible in primary care practice, including blue dyes and radiographic lymphography, this article discusses the indications for lymph node mapping and describes step-by-step techniques.<\/p>\n
Take-Home Points<\/strong><\/p>\n <\/div><\/div><\/p>\n In veterinary oncology, identification of metastatic disease allows for accurate patient staging<\/a> and guides both treatment and prognostication. For many skin cancer types, such as squamous cell carcinoma, mast cell tumors, and melanoma, identification of metastatic lymph nodes is important in understanding the extent of disease to guide treatment recommendations (<\/span>TABLE 1<\/b><\/span>). In some cases, removing metastatic lymph nodes may also have survival benefit.3,4,7,8,10-12<\/sup><\/span><\/p>\n .<\/span><\/p><\/div>\n The gold standard for assessing lymph nodes for metastasis is histopathology.13,14<\/sup> In most cases, the entire lymph node is removed, or extirpated, to allow full assessment for evidence of disease.15<\/sup> Studies in human medicine have shown the accuracy of ultrasonography, computed tomography, and palpation in detecting lymph node metastasis to vary depending on tumor type.16,17<\/sup> Fine-needle aspiration and cytology of the lymph nodes<\/a> is considered an inferior method of assessing for metastatic disease; reasons for inaccurate results include failure to reach the metastatic region of the lymph node during sampling and failure to sample the metastatic lymph node when sampling a single lymph node within a chain or cluster.18-20<\/sup><\/span><\/p>\n Two main challenges exist when attempting to identify and remove the lymph nodes involved with draining malignant skin tumors. The first is that the first draining lymph node, or sentinel lymph node (SLN), is not always the lymph node(s) closest to the tumor (regional lymph node). The second is identifying and surgically removing the correct lymph node(s).<\/span><\/p>\n The SLN can be identified using a technique called SLN mapping, or lymphography. Preoperatively, this technique uses injection of a contrast agent and subsequent radiographs or advanced imaging to identify uptake of the agent by lymph nodes; intraoperatively, dye is used to aid in visual identification of the SLN. Each has limitations; therefore, it is recommended that clinicians use a combination of preoperative and intraoperative lymphography to guide which lymph node(s) to remove.<\/p>\n The equipment and supplies needed for both preoperative and intraoperative SLN mapping are shown in <\/span>FIGURE 1<\/b><\/span>. The syringe size (1 to 5 mL) depends on the volume to be injected; use of a ruler and skin marker depends on clinician preference. For preoperative mapping, nonsterile gloves may be used in place of sterile gloves if desired.<\/span><\/p>\n\n
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<\/a>Identifying Metastatic Lymph Nodes<\/h2>\n
Identifying the Sentinel Lymph Node<\/h2>\n
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