Peer Reviewed SURGICAL SKILLS: LYMPHADENECTOMY Lymphadenectomy: Overview of Surgical Anatomy & Removal of Peripheral Lymph Nodes Tanya Wright, DVM, and Michelle L. Oblak, DVM, DVSc, Diplomate ACVS (Small Animal), ACVS Fellow of Surgical Oncology Ontario Veterinary College, University of Guelph In the field of veterinary oncology, lymphadenectomy INDICATIONS FOR LYMPH NODE can play an important role in our veterinary BIOPSY patients with regard to clinical staging, determining Research suggests that lymph node biopsy should prognosis, developing treatment plans, and be performed to determine regional lymph node decreasing tumor burden. status in patients in which malignant disease is a For a given oncologic disease, peripheral regional possibility.1-6 Lymph node biopsy methods include: lymph nodes should be carefully palpated for • Fine-needle aspiration and cytology enlargement, asymmetry, and degree of fixation. • Needle core biopsy While identification of palpably enlarged lymph • Incisional biopsy nodes is typically straightforward, identification and • Excisional biopsy. extirpation of peripheral lymph nodes when they are of normal size can be challenging. Palpation Techniques for surgical excision of peripheral Abnormal lymph node palpation may be helpful for lymph nodes are infrequently described in the raising suspicion for metastatic disease; however, literature. The goal of this article is to describe clinical judgment regarding metastasis to local the location and anatomy of commonly removed lymph nodes should not be based on palpation peripheral lymph nodes and illustrate effective alone, as lymph node size is not an accurate strategies for surgical excision of these nodes. predictor of metastasis.1-3 GENERAL LYMPH NODE FUNCTION & Aspiration & Cytology ANATOMY Lymph node fine-needle aspiration and cytology The lymph node is the structural and functional unit is easy, quick, noninvasive, and has been shown to of the lymphatic system. Lymph nodes act as a filter of be highly sensitive and specific for detecting solid lymph, as well as a germinal center for lymphocytes. tumor metastasis to regional lymph nodes.2,3 Lymph nodes are typically firm, smooth, and Within a lymph node, metastatic lesions may ovoid or bean-shaped. They contain a poorly be focal and missed by cytology. If metastasis is defined cortex and medulla, and have a concave suspected clinically, but cytology is negative for hilus region, which contains efferent lymphatics and neoplastic cells, histopathology is warranted to blood vessels. ensure the cytology sample is representative of the Lymph flows from lymph capillaries via the entire lymph node. afferent lymph vessels to the regional lymph node, In addition, for head and neck lesions, the and efferent lymph vessels leave the lymph node, sensitivity of cytology is only reported for mandibular carrying lymph that is filtered and enriched with lymph nodes. Access to the retropharyngeal lymph lymphocytes. nodes for aspiration can be challenging and typically Groups of neighboring lymph nodes that occur requires ultrasound guidance, which may be a in the same region of the body and receive afferent limitation of this technique. vessels from approximately the same region, in Mixed cell responses are often hard to interpret, CE as some cells do not readily exfoliate and, in some most species, are known as lymphocentrums or Article lymphocenters. cases, reactive hyperplasia can mimic neoplasia. 20 TODAY’s VeTERINARY PRACTICE | July/August 2016 | tvpjournal.com SURGICAL SKILLS: LYMPHADENECTOMY Peer Reviewed Needle Core & Incisional Biopsy We rarely perform needle core or incisional biopsies unless the lymph node is signifi cantly enlarged, due to the relative ease of excisional biopsy. If a needle core or incisional biopsy is performed, prolonged direct pressure to the lymph node or closure of the capsule may be required to address any hemorrhage that occurs. Excisional Biopsy When possible, excisional lymph node biopsy is considered the preferred method to determine if metastatic disease is present. Excisional lymph node biopsy is also warranted in patients with metastatic neoplasia in which lymph node biopsy is not only useful for diagnosis, but also to decrease tumor burden prior to adjunctive therapy. SELECTION OF LYMPH NODES Common peripheral lymph node biopsy sites (Figure 1) include: FIGURE 1. Illustration of the pertinent regional anatomy of the neck • Mandibular lymph nodes • Medial retropharyngeal lymph nodes In dogs and cats, the medial retropharyngeal • Superficial cervical (prescapular) lymph nodes lymph node group serves as the collecting center • Popliteal lymph nodes. for the head, receiving drainage from the lateral The mandibular lymph nodes are the easiest to retropharyngeal, parotid, and mandibular nodes. palpate and, subsequently, the easiest to surgically Based on lymphatic drain patterns, the medial remove. retropharyngeal lymph node may yield the most Techniques for removal include sharp or blunt tissue can be carefully grasped with thumb Lymphadenectomy: dissection or careful electrocautery, aiming to forceps, Allis tissue forceps, or a stay suture stay immediately outside the lymph node capsule placed through the node, depending on the size Approach & (Figure 2). Cotton tip applicators (ie, cotton and fragility of the node. Care must be taken to swabs) can be used to perform blunt dissection avoid crush artifact of the lymph node. Supplies of small or more delicate lymph nodes. Ligation of the lymph node’s blood supply, Maintaining a grip on the lymph node to provided via the vascular hilus, can be achieved be removed is recommended to avoid losing its using absorbable monofi lament suture (ie, location. To maintain a tight hold on the desired 4-0 or 3-0 PDS, depending on size) or with lymph node and aid in dissection, the perinodal electrocautery. A B C FIGURE 2. Extirpation of the lymph node is accomplished with a combination of blunt and sharp dissection (A). The lymph node is grasped with fi ngers or the perinodal tissue to prevent damage, as it can be very friable (B). Electrocautery, if avail- able, can be useful for dissection and coagulation of small vessels and the vascular bundle (C). tvpjournal.com | July/August 2016 | TODAY’S VETERINARY PRACTICE 21 SURGICAL SKILLS: LYMPHADENECTOMY information regarding regional metastasis of oral number and position, small in size, and require a neoplasms.7 However, these lymph nodes cannot be much more extensive dissection for removal. palpated when normal in size and are one of the most The popliteal lymph node is easily located caudal challenging types of lymph nodes to identify surgically. and distal to the stifle. This lymph center is typically In the neck, commonly, only the superficial present as a single node and it is the easiest lymph cervical lymph nodes are excised, as the deep node to sample when peripheral lymphadenopathy is cervical lymph nodes are deeply located, variable in present. MANDIBULAR LYMPH NODE CENTER typically long and ovoid, approximately TECHNIQUE 10 mm wide by 20 mm long, and flattened Anatomy transversely. The mandibular lymph nodes (Figure 3 and Table) are: Patient Positioning • Bilateral Position the patient in: • Comprised of groups of 2 or 3, and occasionally up • Lateral recumbency, with the affected side up, for to 5, nodes unilateral removal • Superficial in location. • Dorsal recumbency for bilateral removal (see The two most prominent and predictable lymph Patient Positioning, Medial Retropharyngeal nodes in the group lie immediately dorsal and ventral Lymph Node Center, page 24). to the facial vein: If bilateral lymphadenectomy of the mandibular • The dorsal mandibular lymph node is typically and retropharyngeal lymph nodes is desired, the flattened, 3-sided, and approximately 10 mm long midline ventral cervical technique is recommended in the dog. (see Surgical Technique, Medial Retropharyngeal • The ventral mandibular lymph node is Lymph Node Center, page 24). TABLE. Key Anatomical Landmarks for Lymph Nodes TECHNIQUE LYMPH NODE LANDMARKS Mandibular lymph • Just ventral and caudal to angular process of node center mandible • Caudoventral to masseter muscle • Located on either side of facial vein, craniomedial to bifurcation of linguofacial vein bifurcation • Cranial to mandibular salivary gland • Craniolateral to the basihyoid Medial • Ventral to wing of the atlas retropharyngeal • Bound by digastricus muscle cranially, longus lymph node colli muscle dorsally, and larynx and pharynx center ventromedially • Medial, dorsal, and slightly caudal to the easily palpable mandibular salivary gland • Medial and immediately caudal to linguofacial vein bifurcation • Caudal to hyoid venous arch Superficial • Located at cranial edge of supraspinatus muscle, just cervical under the omotranversarius muscle (prescapular) • Superficial cervical artery and vein are located medial FIGURE 3. Position of the mandibular (A) and lymph node to caudal portion of lymph node center medial retropharyngeal (B) lymph nodes relative to the anatomy of the neck, mandibular salivary Popliteal lymph • Located, along with surrounding subcutaneous fat, in gland (C), caudal extent of the mandible (D), node center the popliteal space caudal to stifle joint thyroid cartilage (E), cricoid cartilage (F), trachea • Lateral saphenous vein courses proximally to (G), external jugular vein (H), hyoid venous arch gastrocnemius muscle to the level of popliteal lymph (I), facial vein (J), and thyroid gland (K). node caudal to stifle joint