Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.
Issue link: http://todaysveterinarypractice.epubxp.com/i/840151
68 IMAGING ESSENTIALS PEER REVIEWED The internal iliac (formerly "hypogastric") and sacral lymph nodes are found between the origin of the external and internal iliac arteries and alongside the median sacral artery, respectively. These lymph nodes receive afferent lymphatics from the rectum, pelvic canal, anal glands, and perineal region. Although these nodes are not routinely identified, this area should be evaluated as metastases from tumors in these regions do occur with enlargement of these specific lymph nodes, and the internal iliac lymph nodes may then be appreciated. 18,19 Unless severely enlarged, the sacral lymph nodes are typically not visible ultrasonographically due to their position in the pelvic canal. They are obscured by the shadow from the pubic bones. Visceral Nodes The jejunal or mesenteric lymph nodes are the largest lymph nodes in the abdomen. They are located around the cranial mesenteric artery and vein in the right cranial to middle abdomen just to the right of the umbilicus ( Figure 11 ). These lymph nodes are vermiform, cylindrical, and elongated and measure up to 0.5 cm thick and up to 3 to 4 cm long. 20 Contrast ultrasonography has been described to better characterize lymph node enlargement patterns. 21 The jejunal lymph nodes are usually reactive and enlarged in young dogs and cats up to 1 year of age ( Figure 11 ). 3,4,13 They can be heteroechoic with multiple peripheral hypoechoic nodules. The jejunal or mesenteric lymph nodes are commonly enlarged in inflammatory (eg, secondary to inflammatory bowel disease), infectious (eg, pythiosis), and neoplastic (eg, metastatic disease from adenocarcinoma or involvement in multicentric round cell neoplasia; Figures 12 and 13 ) disorders of the gastrointestinal tract. The appearance of the cisterni chyli has been reported as an anechoic tubular structure, without detectable flow, at the right dorsolateral aspect of the aorta at the level of the cranial mesenteric artery. The shape and size of the cisterna chyli in an individual dog can vary during the same ultrasound examination and between different examinations. 22 SUMMARY As in all cases of abdominal disease, increases or decreases in overall echogenicity are subjective, and sonographers must be familiar with how the peritoneal and retroperitoneal spaces and abdominal lymph nodes appear in normal dogs and cats when scanned with their machines. Severe enlargement of abdominal lymph nodes is usually an indicator of neoplasia (multicentric or metastatic); however, mild to moderate enlargement can indicate either neoplasia or reactive lymphadenopathy secondary to inflammation or infection. FIGURE 11. Mildly enlarged (10 mm) mesenteric lymph nodes (arrows) from a 4-month-old dog. This degree of mild lymphadenomegaly is normal in puppies. Clifford R. Berry Clifford R. Berry, DVM, DACVR, is a professor of diagnostic imaging at University of Florida College of Veterinary Medicine. His research interests include cross-sectional imaging of the thorax, nuclear medicine, and biomedical applications of imaging. He received his DVM from University of Florida and completed a radiology residency at University of California–Davis. Elizabeth Huynh Elizabeth Huynh, DVM, is a diagnostic imaging resident and graduate student at University of Florida College of Veterinary Medicine. Her interests include ultrasonography, cross-sectional imaging, and nuclear medicine. She received her DVM from Ross University, finished her clinical year at Ohio State University, and completed a diagnostic imaging internship at Animal Specialty and Emergency Center in Los Angeles, California. Danielle Mauragis Danielle Mauragis, CVT, is a radiology technician at University of Florida College of Veterinary Medicine, where she teaches diagnostic imaging. She coauthored the Handbook of Radiographic Positioning for Veterinary Technicians and received the Florida Veterinary Medical Association's 2011 Certified Veterinary Technician of the Year award. To see the references for this article, please visit tvpjournal.com.