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Home , Gastric lymph nodes, Ileocecal fold, Lymph node

ULTRASONOGRAPHIC OF ABDOMINAL NODES IN THE NORMAL CAT

ELKE SCHREURS,KATHELIJN VERMOTE,VIRGINIE BARBERET,SYLVIE DAMINET,HEIKE RUDORF,JIMMY H. SAUNDERS

Lymph nodes are essential structures to be evaluated in an ultrasonographic examination of the feline . It was hypothesized that current technical proficiency would allow all feline abdominal lymph nodes to be identified ultrasonographically. Ten clinically normal, adult, domestic shorthair cats were examined using real- time compound ultrasonographic imaging. The medial iliac lymph nodes were visible in 100% of the cats, the jejunal lymph nodes in 90%, the hepatic lymph nodes in 70%, the aortic lumbar, the splenic, and the pan- creaticoduodenal lymph nodes in 60% each, the ileocecal and the colic lymph nodes in 50% each, and the renal, the gastric, the sacral and the caudal mesenteric lymph nodes in 40%, 30%, 20%, and 10% of the cats, respectively. The inconsistent presence of lymph nodes, their poor echocontrast and interposed gas of the explain the lower percentages of identification. The ultrasonographic length and diameter of the lymph nodes were determined. The majority of these measurements corresponded to those in the lit- erature. We conclude that ultrasonography is a valuable tool for the identification and evaluation of most abdominal lymph nodes in the normal cat. Average ultrasonographic measurements are presented as a preliminary guideline for normal feline abdominal lymph nodes. Veterinary Radiology & Ultrasound, Vol. 49, No. 1, 2008, pp 68–72.

Key words: abdomen, cat, lymph nodes, ultrasonography.

Introduction lymph nodes in the normal cat as well as the frequency one succeeds in identifying them. HE ANATOMY OF abdominal lymph nodes in the cat has Tbeen described, and minor variations exist concerning presence, location, size, and shape of the lymph nodes.1–4 Materials and Methods Ultrasonographic information on the appearance of Ten cats were imaged. All cats had a clinical problem normal feline and canine lymph nodes is available: they other than abdominal disease. The general condition, clin- have an elongated shape and homogeneous echotexture, ical examination, and complete blood count were normal, and are slightly hypoechoic compared with mesenteric fat.5 and tests for FIV and FeLV were negative. All cats were In the dog, the ultrasonographic examination of normal adult, domestic shorthair cats with age between 1 and 10 abdominal lymph nodes has been described.6 Criteria have years. Gender was not a selection criterion. Four uncoop- been defined to differentiate normal and diseased canine erative cats were sedated with medetomedine (100 mg/kg superficial lymph nodes, using B-mode and Doppler ultra- intramuscular). The ultrasonographic examinations were sonography (US).7 performed by one and the same observer (J.H.S.), who We hypothesized that advances in ultrasonographic scanned the abdomen of all cats. Real-time compound US technology might enable to obtain more information re- with a 7–14 MHz linear transducer was used.Ã Machine garding ultrasonographic imaging of abdominal lymph settings were adjusted for optimal image quality. nodes in the cat. Hence, the aim of this study was to further During the examination, particular attention was given describe the ultrasonographic anatomy of the abdominal to identification of the abdominal lymph nodes, based on available anatomic description (Fig. 1a and b).1 Aortic From the Department of (Schreurs, Barberet, Rudorf, lumbar, renal, hepatic, splenic, gastric, pancreaticoduode- Saunders) and the Department of Small Animal Medicine (Vermote, Daminet), Faculty of Veterinary Medicine, Ghent University, Salisbury- nal, jejunal, ileocecal, colic, caudal mesenteric, medial iliac, laan 133, Merelbeke B-9820, Belgium. and were evaluated. The aortic lumbar Presented at the 2005 European Association of Veterinary Diagnostic lymph nodes are oriented along the abdominal aorta and Imaging Meeting, Naples, Italy, and at the 2005 British Medical Ultra- sound Society Meeting, Manchester, UK. caudal vena cava, spread between the diaphragm and the Address correspondence and reprint requests to Jimmy H. Saunders, deep circumflex iliac . One to four of these lymph Medical Imaging, Faculty of Veterinary Medicine, Ghent University, nodes are associated with the renal vessels and are named Salisburylaan 133, Merelbeke B-9820, Belgium. E-mail: Jimmy.Saun- [email protected] renal lymph nodes. The hepatic lymph nodes are located at Received December 1, 2006; accepted for publication June 16, 2007. doi: 10.1111/j.1740-8261.2007.00320.x ÃLogiq 7, GE Medical Systems, Milwaukee, WI.

68 Vol.49,No.1 ULT RA S OU N D O F FELINE ABDOMINAL LYMPH NODES 69

Fig. 1. (A) Feline parietal abdominal lymph nodes with surrounding anatomy. Right is to the left of the image, cranial is to the top of the image. LN, (s). (B) Feline visceral abdominal lymph nodes with surrounding anatomy. Adapted from Barone1 with permission. Right is to the left of the image, cranial is to the top of the image. LN, lymph node(s). the junction of the splenic and gastroduodenal with the number of cats in which a particular lymph node could the portal and in the hilus of the . The splenic be identified. For each lymph node, the maximal length lymph nodes can be found adjacent to the splenic vessels in and the maximal diameter were measured once in each cat. the hilus of the . The are em- The maximal diameter was defined to be perpendicular to bedded in the lesser omentum along the lesser curvature of the maximal length. Depending on where the parameters the , adjacent to the cardia or occasionally adja- were largest, length and diameter were identified on the cent to the pylorus. The pancreaticoduodenal lymph nodes same image or on two separate images. Subsequently, the are oriented at the caudal aspect of the pylorus, where the mean maximal length and the mean maximal diameter of cranial pancreaticoduodenal and the right gastroepiploic each lymph node were calculated by averaging the mea- veins meet. One or two pancreaticoduodenal lymph nodes surements of the 10 cats. If more than one lymph node was may be present adjacent to the right pancreatic lobe. Mul- identified in one location, the largest one was measured. tiple jejunal lymph nodes are located adjacent to the cranial If only one lymph node was visible, it was considered mesenteric and the origin of the jejunal arteries at representative of the group of lymph nodes. As soon as one the root of the . In 50% of the cats, some lymph lymph node was identified during the ultrasonographic nodes can be found along the jejunal vessels in the more examination, no further attempt was made to find other distal part of the mesentery, near the and the lymph nodes of the same group. . The ileocecal lymph nodes are embedded in the ileocecal fold at both sides of the concavity of the . The mesocolon contains the colic lymph nodes near the Results ascending and transverse colon, and the caudal mesenteric The results are summarized in Table 1 and compared lymph nodes near the descending colon. The medial iliac with the range of normal anatomic values.1–4 lymph nodes are found adjacent to the abdominal aorta The medial iliac and the jejunal lymph nodes were the and the caudal vena cava. They are caudal to the deep most frequently identified lymph nodes, visible, respective- circumflex iliac artery and vein, and cranial to the external ly, in 100% and 90% of the cats. The caudal mesenteric iliac artery and common iliac vein. The sacral lymph nodes and the sacral lymph nodes had the lowest detection fre- are located caudal to the origin of the internal iliac arteries quencies, which were 10% and 20%, respectively. Other and at the origin of the median sacral artery. They may detection frequencies ranged between 30% and 80%. follow the course of these vessels. Thelengthofalllymphnodeswasinaccordancewith A normal lymph node was recognized ultrasonograph- the anatomy literature,1–4 except for one ileocecal lymph ically as a hypoechoic, homogeneous, elongated structure node. This lymph node had a length of 23.2 mm, which in its expected anatomic location. A record was made of exceeds the reported 15 mm. 70 SCHREURS ET AL. 2008

Ta ble 1. Ultrasonographic Frequency of Detection and Measurements of Feline Abdominal Lymph Nodes

Frequency (%) USÃ Length (mm) Anatomic Length (mm) USÃ Diameter (mm) Anatomic Diameter (mm) Aortic lumbar 60 9.9 (2.1–16.7) 0.5–18 3.2 (0.3–7.4) 3–4 Renal 40 6.1 (4.7–7.7) 0.5–14.5 3.5 (2.9–4.1) Not available Hepatic 70 7.6 (5.9–9.5) 1.5–30.5 2.9 (2.5–3.6) 10 Splenic 60 8.4 (5.0–11.2) 2–22 3.2 (1.9–4.8) 2–22 Gastric 30 5.1 (4.6–6.4) 1–20 1.9 (1.9–1.9) Not available Pancreaticoduodenal 60 8.4 (6.6–13.0) 3–15.5 4.6 (3.6–6.2) 5 Jejunal 90 20.1 (11.4–39.0) 5–80 5.0 (2.8–7.2) Max 10 Ileocecal 50 11.8 (6.7–23.2) 3–15 4.1 (2.7–4.8) 5–9 Colic 50 9.0 (4.6–12.1) 1–30 3.1 (1.9–5.2) Not available Caudal mesenteric 10 6.0 (6.0–6.0) 5–15 2.1 (2.1–2.1) 5–15 Medial iliac 100 13.5 (5.0–23.3) 1–28 4.5 (1.3–14.0) 2–7 Sacral 20 9.6 (9.2–10.0) 1–28 2.2 (1.7–2.7) Not available

Results of the ultrasonographic examination of the abdomen of 10 cats. The ultrasonographically measured maximal length and diameter are represented as mean and range. The ranges of anatomic measurements out of literature are available for comparison. ÃUltrasonographic.

The ranges for normal lymph node diameters are avail- area.10 This is higher than the 50% frequency reported in able in anatomy texts for aortic lumbar, splenic, jejunal, our study. Nevertheless, the diameter of both lymph nodes ileocecal, caudal mesenteric, and medial iliac lymph ranged between 1.9 and 4.9 mm, which was similar to our nodes1–4 and matched the measured diameter in 23/36 range of maximal diameter, 1.9–5.2 mm. individual lymph nodes (diameter of one ileocecal lymph In the dog, normal abdominal lymph nodes are difficult node was lost during the procedure). In 11/36 lymph nodes, to identify due to their small size and as their echogenicity the diameter was below the anatomic range, and 2/36 is similar to those of the surrounding tissues.6 Only the lymph nodes had a diameter above the anatomic range. medial iliac and the jejunal lymph nodes are regularly While the reported approximate diameters of the hepatic identified. In another study, the medial iliac lymph nodes and the pancreaticoduodenal lymph nodes are 10 and were identified in 45% (left) and 82% (right) of 11 normal 5 mm, respectively, the corresponding ranges in our study dogs.11 In our study, at least one medial iliac lymph node were 2.5–3.6 mm, for six hepatic lymph nodes (diameter of was found in each cat and a jejunal lymph node was visible one hepatic lymph node was lost during procedure), and in nine of 10 cats. 3.6–6.2 mm, for six pancreaticoduodenal lymph nodes. Not all abdominal lymph nodes were consistently found in cats in the present study. According to anatomic de- scriptions, most abdominal lymph nodes are present in Discussion individual cats, although their number may be variable. Real-time compound imaging, a technique based on Individual cats may occasionally be missing the aortic multiple angles of insonation per scan plane, was used lumbar, renal, splenic, gastric, ileocecal, or sacral lymph in this study. Compared with conventional B-mode US, nodes.1–3 However, in this study, they were identified, re- it produces superior border definition of rounded struc- spectively, in 60%, 40%, 60%, 30%, 50%, and 20% of the tures, less image speckle and improved soft tissue cats. It is not known if the lymph nodes that could not be contrast.8 These advantages are beneficial in imaging seen in our 10 cats were actually absent or just not detected lymph nodes, known for having poor contrast with sur- during the ultrasonographic examination, as no gold stan- rounding tissue. dard for deciding on the presence or absence of the nodes is Few reports are available on the ultrasonographic char- available. There was no tendency for the lymph nodes with acteristics of normal abdominal lymph nodes in the cat. the lowest detection frequencies to be identified within the The appearance of feline gastric lymph nodes has been same individual cat, which would suggest a better visibility described in connection with the normal .9 In that of the abdominal lymph nodes in these specific cats. study, only one gastric lymph node was found craniome- Visceral and vascular landmarks can be used to locate dial to the pylorus. Its largest size was 10 Â 6 mm, while abdominal lymph nodes ultrasonographically. In the liter- our largest measurement was 6.4 Â 1.9 mm. In the same ature, an ultrasonographic map of abdominal vessels is study, the gastric lymph node was identified in six of 20 available for the dog, but not for the cat.12 In our study, we normal cats, which is similar to our study. used both visceral and vascular landmarks. Color or power Regarding the ileocecocolic region in normal cats, all of Doppler sonography was used whenever necessary (Figs. 31 cats had at least two colic lymph nodes identified in this 2–6). Vol.49,No.1 ULT RA S OU N D O F FELINE ABDOMINAL LYMPH NODES 71

Fig . 2. The aortic lumbar lymph nodes area located along the abdominal Fig. 4. The jejunal lymph nodes are located adjacent to the cranial mes- aorta (AA). Length and diameter are indicated by the callipers. Cranial is to enteric artery (CMA) and the origin of the jejunal arteries at the root of the the left of the image. mesentery. Length and diameter are indicated by the callipers. Cranial is to the left of the image. SI, small intestines.

In humans, interposed gas makes perigastric and perisplenic lymph nodes difficult to access ultrasonogra- lumbar aortic, splenic, jejunal, and medial iliac lymph phically.13 A similar problem was noted in our study, with nodes were. The maximal diameters of the individual il- gas obscuring lymph nodes near the stomach, cecum, and eocecal and the caudal mesenteric lymph nodes were con- colon (gastric, pancreaticoduodenal, ileocecal, colic, and sistently lower than those of the anatomic references. Also, caudal mesenteric lymph nodes). Small intestinal loops the maximal diameter of the individual hepatic lymph were not detrimental to lymph node identification, as they nodes did not approach the reference value of 10 mm. No mostly contained mucus and could be displaced during anatomic reference values are available for diameters of scanning. renal, gastric, colic, and sacral lymph nodes. Apart from one ileocecal lymph node, all lymph nodes To our knowledge, the accuracy of ultrasonographic had their lengths falling within the published range.1–4 Not measurement of lymph nodes has not been validated. We all diameters of the individual lymph nodes were in har- propose our measurements as a preliminary guideline of mony with the literature, although the mean diameters of the expected sizes of abdominal lymph nodes in normal

Fig. 3. The hepatic lymph nodes are located in the hilus of the liver (L) and near the junction of the splenic and gastroduodenal veins with the portal Fig. 5. The ileocecal lymph nodes are located on both sides of the cecum vein. The latter are not in the field of view in this image. Length is indicated (C). Length and diameter are indicated by the callipers. Cranial is to the left by the callipers. Cranial is to the left of the image. S, stomach. of the image. I, ileum. 72 SCHREURS ET AL. 2008

Pathologic abdominal lymph nodes are easier to image ultrasonographically because they are usually enlarged, have decreased echogenicity and are more rounded.5,6,14 In advanced disease, they may become irregularly shaped, heterogeneous, and poorly marginated.15 A good optimal knowledge of the lymph node drainage pattern is impor- tant to increase specificity of detected abdominal abnor- malities.1–4 Attempts to characterize abnormal lymph nodes as benign or malignant have lead to numerous ultrasonographic parameters in humans and animals.7,16 It is concluded that in humans the Doppler characteristics described for superficial lymph nodes are difficult to apply to abdominal lymph nodes because of the deeper location of the latter ones.17 To conclude, most of the abdominal lymph nodes in the normal cat can be assessed ultrasonographically. We sug- Fig. 6. The sacral lymph nodes are located caudal to the origin of the gest using the proposed ultrasonographic measurements as internal iliac arteries (IIA). Length and diameter are indicated by the calli- pers. Cranial is to the left of the image. a guideline for the assessment of abdominal lymph nodes in normal cats.

ACKNOWLEDGEMENT cats. This is especially important due to the similar body The authors thank Karen Bonte, DVM, for her enthusiastic support conformation among adult cats of most breeds. at the start of this study.

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