ULTRASONOGRAPHIC ANATOMY OF ABDOMINAL LYMPH 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 abdomen. 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 gastrointestinal tract 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 Medical Imaging (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 sacral lymph nodes 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 arteries. 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, lymph node(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 veins with the number of cats in which a particular lymph node could the portal vein and in the hilus of the liver. 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 spleen. The gastric lymph nodes 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 stomach, 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 artery and the origin of the jejunal arteries at representative of the group of lymph nodes. As soon as one the root of the mesentery. 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 jejunum and the lymph nodes of the same group. ileum. The ileocecal lymph nodes are embedded in the ileocecal fold at both sides of the concavity of the cecum. 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.