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 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 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. An oval lymph node with a short matrix, a reconstruction index of 0.5–1 and a medium fre- axis/long axis ratio >0.5 was classified as rounded. Bilo- quency reconstruction algorithm. Postcontrast images were bar or multilobar lymph nodes were classified as elongated. made 1–13 min following manual injection of 700 mg I/kg Lymph nodes were considered miscellaneous in shape if body weight of iodinated contrast (Iobitridol, XenetixR 612 BEUKERS,GROSSO,VOORHOUT 2013

TABLE 1. Number of Lymph Nodes Identified per Lymph Node Group in Abdominal CT Studies of 19 Dogs with No Suspected Lymphadenopathy

Number and percentage of dogs in which 0, 1, 2, and 3 or more lymph nodes were visible (n = 19 dogs) Lymph node Total number of lymph nodes identified (n = 19 dogs) No lymph node 1 lymph node 2 lymph nodes 3 or more lymph nodes Hepatic 34 1 (5%) 6 (32%) 8 (42%) 4 (21%) Splenic 19 4 (21%) 12 (63%) 2 (10%) 1 (5%) Gastric 12 7 (37%) 12 (63%) 0 (0%) 0 (0%) Panceaticoduodenal 17 6 (32%) 10 (53%) 2 (10%) 1 (5%) Lumbar aortic 31 4 (21%) 5 (26%) 6 (32%) 4 (21%) Renal 4 15 (79%) 4 (21%) 0 (0%) 0 (0%) Medial iliac 42 0 (0%) 0 (0%) 15 (79%) 4 (21%) Internal iliac and sacral 23 5 (26%) 7 (37%) 5 (26%) 2 (10%) Jejunal >55∗ 0 (0%) 0 (0%) 6 (32%) 13 (69%) Ileocolic 18 10 (53%) 3 (16%) 3 (16%) 3 (16%) Colic 0 19 (100%) 0 (0%) 0 (0%) 0 (0%) Caudal mesenteric 22 5 (26%) 7 (37%) 6 (32%) 1 (5%)

∗For the jejunal lymph nodes, the exact number of lymph nodes could not always be reliably assessed.

350, Guerbet Nederland BV, Gorinchem, the Netherlands) into the cephalic vein. Twelve dogs were scanned in dorsal recumbency, seven in ventral recumbency. Short-term ap- nea was induced with manual hyperventilation for all dogs. The number of lymph nodes visible in each lymph node group was variable (Table 1). The total number of identified lymph nodes in each dog ranged from 11 to 22. A colic lymph node was not identified in any of the dogs. At least one hepatic lymph node was visible in most dogs and at least two jejunal and two medial iliac lymph nodes were visible in all dogs. The course of the jejunal lymph nodes and their close relation to the mesenteric vessels and small intestines made it difficult to reliably assess their size and number in many dogs.

Hepatic Lymph Nodes The hepatic lymph nodes were located along the course FIG. 1. Postcontrast transverse CT image of left and right hepatic lymph of the portal vein, between the hilus of the liver and the ter- nodes (arrows) located along the portal vein (asterisk) in a dog. The left side mination of the splenic vein (Fig. 1). Twenty lymph nodes of the dog is on the right side of the image. were located on the left side of the portal vein, 13 on the right side and one on the dorsal side. All except one dog that TABLE 2. Number and Percentage of Lymph Nodes Detected for each had a lymph node at the right side also had one or more Shape Classification Group in Abdominal CT Studies of 19 dogs with no lymph nodes on the left side. Hepatic lymph node shape Suspected Lymphadenopathy was mostly elongated (74%) or rounded (24%) (Table 2). Lymph node Elongated Rounded Miscellaneous Hepatic (n = 34) 25 (74%) 8 (24%) 1 (3%) Splenic (n = 19) 7 (37%) 9 (47%) 3 (16%) Gastric (n = 12) 0 (0%) 5 (42%) 7 (58%) Panceaticoduodenal (n = 17) 2 (12%) 10 (59%) 5 (29%) Lumbar aortic (n = 31) 15 (48%) 8 (26%) 8 (26%) Most splenic lymph nodes (79%) were located along the Renal (n = 4) 1 (25%) 2 (50%) 1 (25%) cranial or dorsal aspect of the splenic vein, approximately Medial iliac (n = 42) 32 (76%) 3 (7%) 7 (17%) Internal iliac and sacral (n = 23) 17 (74%) 5 (22%) 1 (4%) two centimeters from its termination in the portal vein Jejunal (n = 19)∗ 19 (100%) 0 (0%) 0 (0%) (Fig. 2). The other lymph nodes were also located along Ileocolic (n = 18) 4 (22%) 13 (72%) 1 (6%) the splenic vessels, but relatively closer to the . The Caudal mesenteric (n = 22) 4 (18%) 15 (68%) 3 (14%) shape of the lymph nodes was variable, being elongated in ∗Jejunal lymph node values were based on the shape of the largest lymph 37%, rounded in 47%, and miscellaneous in 16%. node detected per dog. VOL. 54, NO.6 CTCHARACTERISTICS OF CANINE ABDOMINAL LYMPH NODES 613

FIG. 2. Postcontrast transverse CT image of a splenic lymph node (white arrow) at the craniodorsal aspect of the splenic vein (black arrow) in a dog. The portal vein is also visible (asterisk).

FIG. 4. Postcontrast transverse CT image of a pancreaticoduodenal lymph node (white arrow), located ventral to the duodenum (black arrow), and near the pylorus in a dog. The (asterisk) is also visible.

Lumbar Aortic and Renal Lymph Nodes Thirty-five lymph nodes were found close to the caudal vena cava and the aorta, between the diaphragm and the deep circumflex iliac artery. In four dogs, a lymph node was found parallel to the right renal artery. These were classified as renal lymph nodes. All other nodes had their longest dimension parallel to the aorta and caudal vena cava. Most of the lymph nodes were present dorsolateral to the aorta or caudal vena cava at the level of the left phrenicoabdominal artery or vein and the right renal artery and vein. Approximately half of the lumbar aortic lymph nodes had an elongated shape (48%). The other half either FIG. 3. Postcontrast transverse CT image of a gastric lymph node (arrow), had a rounded shape or were classified as miscellaneous. located in the lesser curvature of the in the region of the antrum (asterisk) in a dog. This lymph node has an irregular three-dimensional shape and was classified miscellaneous. Medial Iliac Lymph Nodes

Gastric Lymph Node In all dogs, at least one left and one right medial iliac lymph node was identified. In four dogs a total of three The gastric lymph node was always single and located lymph nodes was visible, all of which had two lymph nodes in the lesser curvature of the stomach in the region of the present at the left side. In most dogs, the medial iliac lymph antrum, often closer to the body of the stomach than to nodes were located at the level of and/or caudal to the tri- the pylorus (Fig. 3). The shape was either rounded (42%) furcation of the aorta. The other lymph nodes were located or miscellaneous (58%). more cranially, at the level of and/or cranial to the tri- furcation. Nine lymph nodes extended cranial to the deep circumflex iliac artery.All lymph nodes were located ventral Pancreaticoduodenal Lymph Nodes to the sixth and/or seventh lumbar vertebrae (L6 and/or The pancreaticoduodenal lymph nodes were always lo- L7), except for two that also extended more cranially, ven- cated ventral to the body of the pancreas and/or the duo- tral to the fifth lumbar vertebra (L5). In one dog a lymph denum, close to the pylorus (Fig. 4). The majority of lymph node was present between the left external and internal iliac nodes were rounded (59%) and 29% had a shape classified artery, but at the same level of a larger left and right medial as miscellaneous. iliac lymph node. 614 BEUKERS,GROSSO,VOORHOUT 2013

FIG. 5. Postcontrast transverse CT image of left and right medial iliac lymph nodes (arrows) in a dog. Notice the dorsal and dorsolateral locations of the lymph nodes with respect to the external iliac arteries (asterisk). Both FIG. 6. Postcontrast transverse CT image of two ileocolic lymph nodes lymph nodes also show peripheral enhancement. (arrows) at the medial aspect of the ascending colon (asterisk) in a dog. The position of this image is immediately cranial to the ileocolic junction.

Medial iliac lymph nodes were more often located on the dorsal or dorsolateral aspect of the external iliac arteries trifurcation of the aorta. Few were located lateral or medial than on the lateral aspect (Fig. 5). When located at the to the descending colon. Most of both ileocolic and cau- dorsal aspect, the lymph nodes were in close relation to the dal mesenteric lymph nodes were rounded (72% and 68%, common iliac veins. The majority of the medial iliac lymph respectively). The other lymph nodes had variable shapes. nodes (76%) had an elongated shape. There was a significant correlation between the number of identified lymph nodes per dog and subjective intraab- < dominal fat ranking (rs = 0.83, P 0.0001). More lymph Internal Iliac and Sacral Lymph Nodes nodes were identified in dogs with more intraabdominal fat. A total of 23 lymph nodes were visible along the left There was no correlation between the number of identified = = (43%) and right sides (57%) of the median sacral artery. A lymph nodes and body weight (rs 0.11, P 0.64) or slice = = clear differentiation between internal iliac and sacral lymph thickness (rs 0.07, P 0.76). nodes could not be made. In only one dog two lymph nodes Sizes of the identified lymph nodes are summarized in were found ventral to the sacrum. In the other dogs lymph Table 3. Before contrast administration, most lymph nodes nodes were found ventral to the lumbosacral junction or had a homogeneous structure, but mild heterogeneity was L7. Most lymph nodes were elongated (74%,) or rounded noted in five nodes. Additionally, 11 nodes were more hyper (22%). attenuating in the periphery than centrally. After contrast administration a mild heterogeneous structure was visible in 22 nodes and peripheral enhancement in 25 (Fig. 5). Of Jejunal Lymph Nodes these 25 lymph nodes, eight were medial iliac lymph nodes, In all dogs two or more jejunal lymph nodes were found. and 13 were jejunal lymph nodes. All 11 lymph nodes that The lymph nodes were present along the cranial mesenteric were relatively more hyper attenuating in the periphery be- artery and vein. The two largest nodes all had an elongated fore contrast administration, showed peripheral enhance- shape, some of which were bilobar. The smaller nodes were ment. The attenuation was measured in 100 lymph nodes elongated or rounded. and ranged from 20 to 52 HU before contrast administra- tion (mean 37 HU, median 37 HU), and from 36 to 223 HU after contrast administration (mean 109 HU, median Ileocolic, Colic, and Caudal Mesenteric Lymph Nodes 105 HU). The ileocolic lymph nodes were located at the medial or Discussion dorsomedial aspects of the ascending colon, close to the ileocolic junction (Fig. 6). No colic lymph node could re- In this group of dogs, not all abdominal lymph nodes liably be identified along the transverse colon. Nearly all could be consistently identified on CT. The number of caudal mesenteric colic lymph nodes were located dorsal identified lymph nodes was positively correlated to the or dorsomedial to the descending colon at the level of the amount of intraabdominal fat present, but no relationship VOL. 54, NO.6 CTCHARACTERISTICS OF CANINE ABDOMINAL LYMPH NODES 615

TABLE 3. Mean Lymph Node Length, Width, and Thickness in Abdominal CT Studies of 19 Dogs with no Suspected Lymphadenopathy

Lymph node Length (range) (mm) Width (range) (mm) Thickness (range) (mm) Hepatic (n = 34) 16.1 (4.5–35.0) 6.7 (2.4–10.4) 5.2 (1.7–8.2) Splenic (n = 19) 10.7 (4.0–21.9) 5.7 (3.1–10.5) 4.4 (1.9–8.2) Gastric (n = 12) 8.7 (4.3–14.0) 7.2 (3.3–11.1) 5.3 (2.1–10.0) Panceaticoduodenal (n = 17) 7.8 (3.1–14.0) 5.9 (3.0–11.4) 4.4 (2.7–9.1) Lumbar aortic (n = 31) 9.2 (3.0–21.0) 4.5 (2.0–7.9) 3.1 (1.7–5.9) Renal (n = 4) 8.8 (3.4–14.0) 5.3 (3.0–7.0) 3.1 (1.7–4.0) Medial iliac (n = 42) 22.8 (3.0–56.0) 6.7 (2.4–11.2) 4.6 (1.2–9.6) Internal iliac and sacral (n = 23) 10.3 (4.5–16.0) 4.8 (2.0–9.2) 3.7 (2.0–7.1) Jejunal (n = 19)∗ 42.0 (24.0–65.0)∗ 9.6 (5.0–15.0)∗ 7.1 (4.0–12.3)∗ Ileocolic (n = 18) 9.7 (3.0–19.0) 6.1 (2.7–14.0) 4.9 (2.7–10.6) Caudal mesenteric (n = 22) 8.8 (4.5–14.0) 6.1 (3.8–9.6) 4.5 (2.0–6.4)

∗Mean size and range values for jejunal lymph nodes were based on the largest lymph node detected per dog. between the number of identified lymph nodes and both In our study, a minimum of two jejunal lymph nodes and body weight and slice thickness was found in our dogs. Dogs two medial iliac lymph nodes was detected in all dogs. This included in this study were carefully selected in an attempt is more than what has been reported in ultrasonographic to avoid including patients with lymphadenopathy. How- studies.2–4, 6 This finding is likely explained by the negative ever, histopathologic examination of the identified lymph influence of gas and food in the gastrointestinal tract on ul- nodes was not performed and this was a limitation of this trasonographic detection of small abdominal structures.2,6 study. The retrospective nature of the present study also in- When an increased number of medial iliac lymph nodes troduced other limitations such as variable scanning param- was detected by ultrasonography in a previous report, con- eters and time of scanning after contrast administration. trol dogs could be differentiated from dogs with lymphoma The presence and location of normal abdominal lymph or metastatic lymph nodes.3 However, in our report, more nodes is well described in anatomic textbooks, and except than two medial iliac lymph nodes were visible in 21% of for the gastric, renal, and sacral lymph nodes, all lymph the dogs and this was in agreement with findings reported nodes have been reported to be consistently present.14,19 It in an anatomic textbook.14 Objective data of visibility of is not known whether the gastric, renal and sacral lymph the other lymph nodes is not available for other imaging nodes that were not identified in our 19 dogs were actually modalities. absent or just not detected, while for the other lymph nodes Small differences in location of the medial iliac, internal that were not identified it is assumed that they were present iliac, and were identified when compar- but undetected. Eight of the ten dogs in which no ileocolic ing them to anatomic and ultrasonographic references.3–5,14 lymph node was recorded had lymph nodes present close Medial iliac lymph nodes in this study were almost always to the ileocolic junction, but these could not reliably be dif- located ventral to L6–L7, opposed to the previously re- ferentiated from jejunal lymph nodes. The small size of the ported location ventral to L5–L6. Also, the cranial end lymph nodes, their close relation to other soft tissue struc- of the nodes did not extend as often cranial to the deep tures, the amount of intraabdominal fat and slice thickness circumflex iliac vessels as previously reported.14 Caudally likely had an effect on the visibility of the lymph nodes. We they often extended on the dorsal aspect of the external iliac found that more lymph nodes were visible in dogs that had arteries. The internal iliac lymph nodes were never visible more intraabdominal fat, most likely because fat surround- cranial to L7, opposed to previously published anatomic ing a lymph node makes it easier to differentiate it from descriptions.14 The gastric lymph nodes were located in the adjacent soft tissue structures. In our study there was no lesser curvature at the level of the antrum, similar to previ- correlation between the number of identified lymph nodes ous reports, but were often closer to the body of the stomach and body weight or slice thickness. Ultrasonographic stud- than the pylorus. The location of all other detected lymph ies showed a positive correlation between lymph node size nodes were consistent with previous reports. and body weight.2,4,20 Therefore one could expect more In general, our measurements of the hepatic, splenic, lymph nodes to be visible in larger patients, but this was jejunal, lumbar aortic, medial iliac, and ileocolic lymph not found in our study. This finding may be explained by nodes as presented in Table 3 were lower than published the fact that slice thickness was based on patient size or anatomic data.14 For the other lymph nodes, no reference by the fact that the sensitivity of CT for detecting small values were found in the literature (except for the colic abdominal structures is sufficiently high for the differences lymph node, which was not identified in our study). It is in size of lymph nodes in small and large dogs to be less possible that CT measurements may have been lower due to important. limited visualization of the full length or width of the lymph 616 BEUKERS,GROSSO,VOORHOUT 2013

nodes due to border effacement with adjacent abdominal lymphoid hyperplasia in the paracortex and cortex.24 It is organs or vessels. Also size and shape may be different in not known whether peripheral flow patterns on ultrasound cadavers used for anatomic reference texts. Accuracy of CT or the histologically visible lymphoid hyperplasia could be measurements could also have been influenced by calliper related to peripheral enhancement on CT. In the veterinary placement, an oblique position of lymph nodes in cranio- literature, a heterogeneous and/or ring enhancement caudal direction and slice thickness. Because craniocaudal pattern on CT was previously related to metastatic disease dimension was estimated based on all transverse slices that in canine tracheobronchial lymph nodes.7 Interobserver contained part of the lymph node and the lymph nodes agreement for subjective grading severity of intrathoracic may not have been present in the full thickness of the most lymphadenopathy in dogs with histiocytic sarcoma is only cranial and most caudal slices, this dimension may have moderate.25 In the human literature, a heterogeneous CT been overestimated. Nevertheless, mean medial iliac lymph appearance of neck lymph nodes can also be caused by node length, and width values identified in the current study local areas of fat or hilar fat and is a known pitfall in were consistent with previously published ultrasonographic diagnosing abnormal lymph nodes on CT.26,27 Sensitivity findings.3–5 Jejunal lymph node width was also consistent for detection of normal sized vs. metastatic abdominal with previously reported maximal transverse diameter on lymph nodes in human literature is low.28,29 The clinical ultrasonographic examination.2 significance of a heterogeneous structure or peripheral The shapes of the lymph nodes described in our study enhancement in abdominal lymph nodes and its relation to were similar to those reported by others.2–4, 14 Although abnormal flow patterns as described in ultrasound needs a rounded shape of lymph nodes was reported to be in- to be investigated further in nodes with a histopathological dicative of malignancy,3,18,21 we found rounded abdominal diagnosis. lymph nodes with a short axis/long axis ratio >0.5 in all The X-ray attenuation of lymph nodes before contrast lymph node groups in our dogs (Table 2). Because over- administration as reported here (mean 37 HU, range 20– estimation of the craniocaudal dimensions, as mentioned 52 HU) was similar to that of previously reported canine before, also influences the short axis/long axis ratio, these cervical lymph nodes (36.6 ± 13.3 HU).10 Though mean shapes may not represent the true lymph node shape. All attenuation after intravenous contrast administration was of the reported rounded lymph nodes were relatively small. also similar for abdominal and cervical lymph nodes (109 The relationship between size and a rounded shape on CT HU and 110.3 HU, respectively), the range that was mea- needs further investigation for discriminating normal from sured in our study was very broad. A large variation in time abnormal lymph nodes. after scanning was most likely responsible for this. Post- Before contrast administration, 11 nodes were more hy- contrast scans were delayed in some of our patients where per attenuating in the periphery than centrally. This could the abdomen was not the primary region of interest or be explained by fat in the hilus of the nodes.10,15 To the multiphase scans were performed before scanning the com- authors’ knowledge, differences in CT attenuation of the plete abdomen. Differences in attenuation between normal lymph node cortex and medulla have not been previously and abnormal lymph nodes have been described in the hu- reported. Though no pronounced heterogeneous structure man literature,30 but have not been investigated in dogs. was observed, mild heterogeneity was observed in some Severe lymph node enhancement was described in a dog nodes before and after contrast administration. Peripheral with granulomatous lymphadenitis of a tracheobronchial enhancement was visible in 25 nodes and was mainly lymph node,7 but no HU values were reported. The clinical present in jejunal and medial iliac lymph nodes, the largest significance of the lymph nodes with pronounced contrast nodes of the abdomen. A possible explanation could again enhancement in our study is not known. Normal and ab- be hilar fat, as 11 of 25 lymph nodes were more hyper normal tracheobronchial lymph nodes that did not show attenuating in the periphery than centrally before contrast contrast enhancement have been previously reported,7 but administration. Areas of abcessation, necrosis, cyst forma- this was not found in any of the lymph nodes in our tion, haemorrhage, or foci of mineralization can cause a study. heterogeneous structure in inflamed or neoplastic lymph In conclusion, abdominal CT lymph node locations de- nodes.15 Additionally, abnormal enhancement patterns scribed in this study were generally in agreement with those can be caused by circulation disruption and can be seen in described in the anatomic literature. Lymph node visibil- malignancy.18,22 Ultrasonographic examination of normal ity, size, shape, structure and X-ray attenuation in pre- ad lymph nodes usually shows a hilar flow pattern whereas postcontrast CT images were variable, although none of the a peripheral flow pattern is more often seen in malignant lymph nodes were evaluated histopathologically to confirm lymph nodes.18,23 Inflammation in the draining area of a normal status. Significantly more lymph nodes were visible lymph node can trigger an immunological response causing in dogs with more intraabdominal fat. VOL. 54, NO.6 CTCHARACTERISTICS OF CANINE ABDOMINAL LYMPH NODES 617

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