COMPUTED TOMOGRAPHIC CHARACTERISTICS OF PRESUMED NORMAL CANINE ABDOMINAL LYMPH NODES MARTIJN BEUKERS,FEDERICO VILAPLANA GROSSO,GEORGE VOORHOUT Though identification of lymph nodes is essential in staging cancer patients, little has been reported about the CT features of canine abdominal lymph nodes. The purpose of this retrospective study was to describe the visibility, location, and characteristics of abdominal lymph nodes in abdominal CT studies of dogs considered unlikely to have lymphadenopathy. The relationship between the number of identified lymph nodes and intraabdominal fat ranking, body weight, and slice thickness was also investigated. A total of 19 dogs were included. At least two jejunal lymph nodes and both left and right medial iliac lymph nodes were identified in all dogs. Colic lymph nodes were not identified in any of the dogs. Visualization of all other lymph nodes varied. There were significantly more lymph nodes visible in dogs with more intraabdominal fat (P < 0.0001). No correlation between the number of identified lymph nodes and body weight (P = 0.64) or slice thickness (P = 0.76) was found. Though most of all identified lymph nodes had an elongated shape, a rounded shape was most common in splenic, pancreaticoduodenal, renal, ileocolic and caudal mesenteric lymph nodes. Most lymph nodes had a homogeneous structure before and following the intravenous administration of contrast medium. Some lymph nodes had a slightly irregular structure or were relatively more hyper attenuating in the periphery than centrally before and/or after contrast administration. Mean attenuation before contrast was 37 Hounsfield Units (HU) (range 20–52 HU), and 109 HU after contrast (range 36–223 HU). Findings indicated that the CT visibility, characteristics of different abdominal lymph nodes may be variable in dogs. C 2013 Veterinary Radiology & Ultrasound. Key words: abdomen, CT, dogs, lymph node. Introduction bar, iliosacral, and iliofemoral lymph centers. The visceral group contains the celiac, cranial mesenteric, and caudal N ESSENTIAL PART OF staging canine cancer patients mesenteric lymph centers. It has been reported that some A is the evaluation of regional and distant lymph abdominal lymph nodes can be detected more frequently on 1 nodes. Ultrasonographic appearance of several abdom- CT than others,15 but no objective data were found in the 2–5 inal lymph nodes has been described, but food and literature. The purpose of the present retrospective study gas in the gastrointestinal tract may have a negative ef- was to describe the visibility, location, and characteristics fect on the ultrasonographic detection of small abdomi- of abdominal lymph nodes in CT studies of adult dogs that 2,6 nal structures. In dogs, CT has proved to be a valuable were considered unlikely to have lymphadenopathy. We hy- imaging modality for the evaluation of tracheobronchial pothesized that not all lymph nodes would consistently be 7–9 lymph node metastasis. Computed tomographic visibil- identified in previously described anatomic locations, and ity and appearance of cervical lymph nodes have also been that more lymph nodes would be visible in dogs with more 10 described. Little is known about the CT features of ca- intraabdominal fat and/or a higher body weight, and when 11–13 nine abdominal lymph node abnormalities. In a previ- thinner CT slices were used. ous report of dogs with insulinomas, CT was able to detect more metastatic lymph nodes than ultrasonography and Single-Photon Emission Computed Tomography, but also Materials and Methods identified many false-positive lesions.13 Imaging data from dogs that underwent an abdominal Lymph nodes of the abdomen are divided in a parietal CT before and following the intravenous administration of and visceral group.14 The parietal group includes the lum- contrast medium at the Division of Diagnostic Imaging, Faculty of Veterinary Medicine, Utrecht University, be- From the Division of Diagnostic Imaging (Beukers, Grosso, Voorhout), Faculty of Veterinary Medicine, Utrecht University,Yalelaan 10, NL-3508 tween December 2009 and December 2012 were retrieved TD, Utrecht, The Netherlands. from the files. Dogs were selected for analysis if they were Address correspondence and reprint requests to M. Beukers, at the above address. E-mail: [email protected] Received March 1, 2013; accepted for publication May 18, 2013. doi: 10.1111/vru.12075 Vet Radiol Ultrasound, Vol. 54, No. 6, 2013, pp 610–617. 610 VOL. 54, NO.6 CTCHARACTERISTICS OF CANINE ABDOMINAL LYMPH NODES 611 at least 1 year old and there was (1) no primary malig- they could not be put clearly into one of the other two nancy or inflammatory process affecting organs within the categories. Lymph node structure before and following the abdominal cavity and/or pelvic canal, abdominal wall or intravenous administration of contrast medium was clas- perineum, (2) no primary malignancy known to commonly sified as (1) homogeneous, (2) mildly heterogeneous, (3) metastasize to abdominal organs (including mast cell tu- heterogeneous, and (4) relatively more hyper attenuating in mors, melanomas), (3) no multicentric malignancy (includ- the periphery than centrally or, on postcontrast scans, as ing lymphoma, leukemia, and histiocytic sarcoma), (4) no peripheral enhancement. When a lymph node was visible abdominal or pleural effusion, and (5) no motion artifacts on three or more consecutive transverse slices and large due to respiratory movement. enough to fit a region of interest of at least 4 mm2,theX- The scans were reviewed retrospectively using soft tissue ray attenuation was measured in Hounsfield Units (HU) in settings (WL 50, WW 350). Lymph nodes that were in- the central slice. Attenuation was measured before and fol- vestigated included the hepatic, splenic, gastric, pancreati- lowing the intravenous administration of contrast medium, coduodenal, jejunal, ileocolic, colic, and caudal mesenteric using a round or oval region of interest that was made as lymph nodes of the visceral group and the lumbar aortic, re- large as possible. nal, medial iliac, internal iliac (formerly called hypogastric), and sacral lymph nodes of the parietal group.14,16 For each Results lymph center, the number and location of the lymph nodes were recorded by a single observer (M.B.). Lymph node lo- Nineteen dogs met the inclusion criteria. There were cation was described using previously published anatomical three dogs with ectopic ureters, three dogs with portosys- landmarks.14,16 Dogs were subjectively ranked as having the temic shunting, two dogs with pituitary-dependent hyper- least to most amount of intraabdominal fat by a consensus adrenocorticism, two dogs with an inflammatory process of two observers (M.B., G.V.).The relationship between the on the front limb that were initially suspected of a neoplas- number of identified lymph nodes and intraabdominal fat tic process and were screened for metastatic disease, two ranking, body weight, and slice thickness was investigated. dogs with a neoplastic mass of the hind limb (a low grade A Spearman correlation test was performed by one of the fibrosarcoma and a haemangiopericytoma) that showed authors (M.B.) to evaluate statistical dependency.The num- no signs of recurrence or metastatic disease in a 2- and ber of identified lymph nodes per dog and intraabdominal 3-year follow-up period after surgical treatment, one dog fat ranking, body weight, and slice thickness were used as with segmental caudal vena cava aplasia, one dog with a independent variables. Statistical analyses were performed ureter calculus and a dilated renal pelvis, one dog with a with commercially available software (R: A Language and lumbosacral disc herniation that was scanned because of Environment for Statistical Computing. Ver: 2.15.2, R nonspecific pain-related symptoms, one dog with transient Foundation for Statistical Computing, Vienna).17 Results renal hematuria and remission of complaints before a final with P ≤ 0.05 were considered statistically significant. diagnosis was made, one dog with exercise intolerance that For each lymph node identified in CT images, a single was scanned as part of an extensive work-up but complaints observer (M.B.) recorded the size (length, width, and thick- were finally attributed to obesity, one dog with episodic ab- ness), shape, structure, and X-ray attenuation characteris- normal behavior that was finally attributed to neuropathic tics. Transverse dimensions were measured using an elec- pain and one dog with episodic vomiting and hypervolemia tronic calliper on the image containing the largest section of of unknown cause. The sample of dogs contained mixed and the lymph node. Craniocaudal dimensions were estimated pure breed dogs weighing between 3.8 and 50.7 kg (mean by multiplying slice thickness by the number of consecu- 23.8 kg, median 25.0 kg). The ages ranged from 1 to 13 tive transverse slices that contained part of the lymph node. years (mean 5.2 years, median 4.3 years). There were eight Length was defined as the maximal dimension of the lymph females (one intact, seven neutered) and 11 males (seven node, irrespective of its position in the abdomen. Width was intact, four neutered). defined as the second maximal dimension and thickness Computed tomographic images for all dogs were ac- as the remaining dimension perpendicular to the width. quired with the same single-slice helical CT scanner (Philips Lymph node shape was classified into one of three cate- Secura, Philips NV, Eindhoven, the Netherlands). Scans gories: (1) elongated, (2) rounded, and (3) miscellaneous. were made in helical acquisition mode with a slice thick- When an oval lymph node had a width that was half the ness of 3–7 mm and a pitch of 1–1.5, depending on patient length or less (short axis/long axis ratio ≤0.5, as reported size. Technical settings were 100–120 kV, 200–320 mA, 0,7– for ultrasonographic examination of lymph nodes),18 it was 1 s tube rotation time, 170–410 mm field of view, 512 × 512 classified as elongated.