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Abdominal lymph nodes

image of Abdominal lymph nodes
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Abstract

Lymph nodes are part of the lymphatic system, which acts as a defense system, and are found throughout the body. Lymph nodes may become enlarged as a response to infection, inflammatory stimuli or secondary to invasion by other cells, as seen with primary neoplasia or metastases. An evaluation of the lymph nodes is therefore important for staging in all ongoing disease processes, particularly in cancer patients. When an abnormal lymph node is encountered it is important to know which anatomical structures it drains to enable a closer evaluation of these regions. It is also important to know which lymph nodes to examine when a particular organ or region is diseased. Lymph nodes are located close to blood vessels and knowledge of the vessel distribution within the abdomen allows the veterinary surgeon to routinely examine the regions where the major lymph nodes are located. The chapter focuses on Normal abdominal lymph nodes; Radiographic features of abdominal lymph nodes; Ultrasonographic features of lymph nodes; Overview of additional imaging modalities; and Biopsy techniques.

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Figures

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7.1 Superficial visceral and deep visceral abdominal lymph nodes in the dog. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and are printed with her permission.
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7.2 Ultrasonogram showing the vasculature of a normal lymph node.
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7.4 A normal hepatic lymph node (ln) in a cat, with an oval shape and an echogenic hilus, just caudal to the liver (L).
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7.5 A normal splenic lymph node (arrowed) next to the splenic vein. Colour Doppler ultrasonography often aids in the detection of lymph nodes as they are always found close to a vessel and also enables distinction of small lymph nodes from vessels and other structures. A small vessel is seen entering the lymph node in the hilar region.
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7.6 Normal pancreaticoduodenal lymph nodes (arrowed) in a cat. This lymph node is not always visible. The lymph nodes are oval and isoechoic compared with the surrounding organs. d = Duodenum; s = Stomach. a dog. This lymph node is not always visible. The lymph nodes are oval and isoechoic compared with the surrounding organs. d = Duodenum; l = Liver.
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7.7 Normal cranial mesenteric lymph nodes. These nodes are variable in length and the whole node can often not be imaged in one plane due to their elongated, often curving, shape. These lymph nodes are most commonly located near the root of the mesentery, but they may also be seen more peripherally in the omentum. Normal nodes have small amounts of hilar flow or appear avascular.
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7.8 Normal colic lymph nodes (arrowed) in a cat and a dog. These lymph nodes are seen next to (a) the ileum and (b, c) the colon. These lymph nodes are small (<4 mm), oval, isoechoic and have an echogenic hilus. Vessels may be used as landmarks to detect the lymph nodes. C = Colon; i = Ileum.
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7.9 Normal medial iliac lymph node in a dog, located near the aortic bifurcation of the caudal aorta. These lymph nodes are almost always visible. ao = Aorta; cvc = Caudal vena cava; eia = External iliac artery.
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7.10 Normal lymph nodes located adjacent to the aorta. These are variable in number and often small. They may be difficult to detect when normal in size. Colour Doppler ultrasonography may aid in the detection and distinction of normal lymph nodes from vessels and surrounding tissues (e.g. fat).
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7.11 Enlarged sublumbar lymph nodes due to different disease processes. The soft tissue mass in the sublumbar area of this dog is a reactively enlarged lymph node, most likely secondary to pyometra. However, the diagnosis needs to be verified with cytology and/or biopsy. Ventral displacement of the colon is common with enlarged sublumbar lymph nodes; in this case a metastatic lymph node secondary to an anal gland carcinoma. This dog has generalized lymphadenopathy due to multicentric lymphoma. However, the radiograph only shows signs of sublumbar node enlargement, demonstrating the low sensitivity of abdominal radiography in detecting abnormal lymph nodes. This dog has three soft tissue masses within the abdomen (arrowed). Firstly, the mass visible in the sublumbar area is a medial iliac lymph node containing metastases of a carcinoma in the colon. Secondly, the colon is displaced ventrally and the soft tissue mass superimposed over it is a carcinoma originating from the wall of the colon. Thirdly, there is a visible mass within the mid-abdomen. Gas-filled small intestinal loops are seen partly superimposed over the soft tissue mass. It is not possible to determine the origin of this mass with radiography alone, but the presence of an enlarged mesenteric lymph node was confirmed by ultrasonography. Cytology confirmed metastatic involvement of this lymph node. Soft tissue mass (arrowed) in the caudal abdomen of a cat. The mass is partly superimposed upon the colon. An enlarged sublumbar lymph node may be suspected from this radiograph; however, if this were the case, the colon would be expected to be displaced ventrally. Same cat as in (e). Ultrasonography confirmed that the mass was a granuloma, involving the wall of the colon, due to feline infectious peritonitis.
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7.12 Lateral thoracic radiographs of a cat and a dog with sternal lymphadenopathy. The increased soft tissue opacity (arrowed), centred dorsal to S3 in the cat and dorsal to S2 in the dog, represents enlarged sternal lymph nodes. Enlarged sternal lymph nodes may suggest mammary gland disease or disease processes within the abdomen.
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7.13 An enlarged medial iliac lymph node in a dog with a metastatic mammary gland carcinoma. The node is asymmetrically thickened, hypoechoic compared with the surrounding tissue, and without a visible echogenic hilus.
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7.14 Normal mesenteric lymph nodes in two dogs. This lymph node is almost isoechoic compared with the surrounding fatty tissue, which may make the detection and identification of the lymph node more difficult. In cases where the lymph node is similar to the surrounding tissue, it may be helpful to use Doppler ultrasonography, as lymph nodes are always found close to vessels. Vascularity may also be detected within the suspicious node, thereby differentiating the lymph node from the surrounding fat. In this case a small hilar signal was seen (arrowed).
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7.15 Enlarged colic lymph node in a cat with feline infectious peritonitis. The lymph node is isoechoic with a hypoechoic rim, and contains a few focal hypoechoic areas that result in a heterogenous echopattern. This appearance is not uncommonly seen, particularly with lymphadenitis. A similar appearance is shown in Figure 7.16 .
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7.16 Medial iliac lymph node in a dog with pyometra. The node is slightly enlarged but has maintained a normal shape. It is hypoechoic compared with the surrounding tissue with an echogenic hilus. An echoic nodule (arrowed) is visible at the cranial pole. There is no detectable blood flow within the node. Fine-needle aspiration of the node showed reactive hyperplasia. It is not certain whether the echoic nodule itself was sampled separately. This appearance may suggest necrosis or an accumulation of fat, but cytology and/or histopathology are required for verification of the diagnosis.
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7.17 Lymphadenitis in a mesenteric lymph node of a dog. The node is isoechoic with a hypoechoic rim and has a normal shape. Note the focal hypoechoic areas with echoic bands within them (arrowed). This pattern may be seen with lymphadenitis.
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7.18 Enlarged medial iliac lymph node in a dog. The node has a heterogenous echopattern with both hypo- and hyperechoic areas. The hypoechoic area corresponded to necrosis on histopathology. ao = Aorta; eia = External iliac artery.
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7.19 Medial iliac lymph node in a dog with a metastatic carcinoma. The node is hypoechoic with a slightly asymmetrical enlargement. Note the distal acoustic enhancement, which is often seen in lymph nodes containing necrosis.
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7.20 Normal ileocolic lymph node in a cat. Normal mesenteric lymph node in a dog. Note that in both cases the lymph nodes are located close to vessels and that a small amount of hilar flow is present in the nodes, which is a typical vascular pattern in normal nodes.
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7.21 Reactive hyperplasia in a medial iliac lymph node in a dog with pyometra. The node is oval, slightly hypoechoic and with a moderate amount of primarily hilar flow, which is typically seen with reactive hyperplasia and lymphadenitis.
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7.22 Metastatic medial iliac lymph node in a dog with mammary gland carcinoma. Metastatic lymph node within the omentum, secondary to an adenocarcinoma of the small intestine. Both nodes are hypoechoic and show primarily a peripheral vascular pattern, typical of metastatic nodes. Note that some of the smaller blue colour signals in (b) are artefacts (noise).
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7.23 Medial iliac lymph node in a dog with lymphoma. The node is richly vascularized with a mixed hilar and peripheral pattern, typical of lymphoma nodes. Colour Doppler ultrasonogram of the lymph node. Power Doppler ultrasonogram of the same node. Power Doppler ultrasonography is more sensitive in detecting flow in small vessels with slow flow, thereby often showing more vessels than seen on colour Doppler ultrasonography. However, the technique is more sensitive to blooming artefacts caused by motion. Therefore, it may often be easier to use colour Doppler ultrasonography, particularly in conscious animals. Ao = Aorta; Eia = External iliac artery.
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7.24 Metastatic colonic lymph node in a cat with neoplasia. The node is richly vascularized with a mixed vascular pattern. There is no detected vascularity in the caudal pole of the node. It is not uncommon to find areas of hypoperfusion in metastatic nodes. Areas of hypoperfusion may correspond to areas of necrosis.
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7.25 Different vascular patterns that may be seen in lymph nodes. Normal vascularity with a hilar pattern. Displacement of the hilar vessel, which may be seen due to deposits of cells within the node secondary to, for example, metastases. Peripheral and subcapsular vessels are typical of malignant nodes as metastases are primarily seen in the peripheral areas of the nodes initially. Aberrant feeding vessels are also a sign of malignancy.
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7.26 Spectral Doppler ultrasonography can be used to measure flow velocities in vessels and to calculate the resistive index (RI) and the pulsatility index (PI). The actual values for RI and PI are not shown in this image; however, the tracing shows that the velocity within the vessel is high, suggesting that the RI and PI will also be high. This finding is commonly seen with malignancy. The RI and PI may vary in a lymphoma node but are often found to be around the same values as benign nodes, as seen here.
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7.28 Lymph nodes are rarely seen on radiographs unless severely enlarged. Lateral radiographs of the abdomen of a Great Dane. Note that there are several soft tissue opacities within the abdomen (arrowed). VD radiographs of the abdomen of a Great Dane. The three soft tissue opacities are seen on the right-hand side of the abdomen (arrowed). It is not possible to determine the origin of these opacities by radiography alone, although there was a strong suspicion that one of them would be the right kidney and the other two could be enlarged lymph nodes. This diagnosis was verified by ultrasonography. Typical ultrasonographic appearance of lymphoma nodes. (e) Two mesenteric nodes (arrowed) and (f) lymph nodes caudal to the liver on the right-hand side (arrowed). The nodes are severely enlarged, asymmetrical in size and outline, markedly hypoechoic, and with clearly defined borders towards the surrounding tissue. As involvement of several lymph nodes is common in animals with lymphoma, it may be helpful to evaluate the surrounding nodes. If several lymph nodes with these characteristics are identified, it is almost certain that lymphoma is present.
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7.29 Dog with a recurring grade II mastocytoma that has metastasized to regional and distant lymph nodes. Metastases were found in the popliteal lymph node, the inguinal nodes and the medial iliac nodes. (a) The popliteal node is severely enlarged, around three times its normal size. It has a heterogenous echogenicity and echopattern. There are ill defined hypoechoic areas, which may represent areas of necrosis or tumour growth. Distal acoustic enhancement is present. (b) Colour Doppler ultrasonographic evaluation of the same node shows rich vascularization. There is an increased amount of vascularity in the periphery of the hypoechoic region. (c) This can be seen even more clearly with the use of power Doppler ultrasonography. This finding suggests that the hypoechoic area may represent an area of growing metastases, which may have induced local angiogenesis. (d) Metastases were also found in the medial iliac nodes. This node is not as enlarged as the popliteal node. It is hypoechoic and well defined, but has an increased amount of flow with a mainly peripheral distribution, which may suggest malignancy. However, the diagnosis should still be verified by cytology and/or pathology.
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7.30 Medial iliac lymph node in a dog with generalized multiple myeloma. The metastatic node is severely enlarged, hypoechoic and has an irregularly outlined border. It is not possible to distinguish between different types of malignancy based on the results of ultrasonography. Ao = Aorta; Eia = External iliac artery.
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7.31 Caudal mesenteric lymph node in a cat with a metastatic adenocarcinoma in the descending colon. The node is hypoechoic and well delineated from the surrounding tissue. Distal acoustic enhancement is present. The node is richly vascularized with a mixed hilar and peripheral flow. There is no detectable blood flow in the ventral portion of the node and this may represent a region of hypoperfusion, commonly seen in areas of necrosis.
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7.32 Normal to slightly prominent colic lymph nodes (arrowed) in a puppy with local inflammation of the caudal part of the ileum (arrowheads). Lymph nodes are often more prominent in young individuals and are therefore considered within normal limits in this case.
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7.33 Enlarged hypoechoic mesenteric lymph nodes in a cat with multicentric lymphoma. The border of the lymph node is slightly irregular and there is no detectable echoic hilus.

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