FEASIBILITY OF CONTRAST-ENHANCED ULTRASOUND-GUIDED BIOPSY OF SENTINEL LYMPH NODES IN DOGS HYLTON R. GELB,LYNETTA J. FREEMAN,JACOB J. ROHLEDER,PAUL W. SNYDER Our goal was to develop and validate a technique to identify the sentinel lymph nodes of the mammary glands of healthy dogs with contrast-enhanced ultrasound, and evaluate the feasibility of obtaining rep- resentative samples of a sentinel lymph node under ultrasound guidance using a new biopsy device. Three healthy intact female adult hounds were anesthetized and each received an injection of octafluoropropane- filled lipid microspheres and a separate subcutaneous injection of methylene blue dye around a mammary gland. Ultrasound was then used to follow the contrast agent through the lymphatic channel to the sentinel lymph node. Lymph node biopsy was performed under ultrasound guidance, followed by an excisional biopsy of the lymph nodes and a regional mastectomy procedure. Excised tissues were submitted for histopathologic examination and evaluated as to whether they were representative of the node. The ultrasound contrast agent was easily visualized with ultrasound leading up to the sentinel lymph nodes. Eight normal lymph nodes (two inguinal, one axillary in two dogs; two inguinal in one dog) were identified and biopsied. Lymphoid tissue was obtained from all biopsy specimens. Samples from four of eight lymph nodes contained both cortical and medullary lymphoid tissue. Contrast-enhanced ultrasound can be successfully used to image and guide minimally invasive biopsy of the normal sentinel lymph nodes draining the mammary glands in healthy dogs. Further work is needed to evaluate whether this technique may be applicable in patients with breast cancer or other conditions warranting evaluation of sentinel lymph nodes in animals. r 2010 Veterinary Radiology & Ultrasound, Vol. 51, No. 6, 2010, pp 628–633. Key words: contrast-enhanced ultrasound, image-guided biopsy, sentinel lymph node. Introduction T HE SENTINEL LYMPH node is the first lymph node in a drainage sequence to receive lymphatic drainage from a tumor and is therefore at highest risk for regional me- tastasis. 1 Localization of the sentinel lymph node involves a combination of techniques including preoperative and intraoperative lymphoscintigraphy, indirect lymphography, and peritumoral blue dye injection to stain the lymphatic channels leading up to the sentinel lymph node. 1–4 Over the last decade, contrast-enhanced ultrasound has been used experimentally in dogs, pigs, and rabbits to visualize the lymphatic channels leading to the sentinel lymph node. 5–13 Advantages of using contrast-enhanced ultrasound for sentinel lymph node detection include the ability to directly visualize the node, the increased specificity for first-order lymph nodes, and the lack of ionizing radiation. A com- mon practice for sentinel node detection in human patients is injection of a radiopharmaceutical and blue dye around the tumor site and using a hand-held gamma probe to lo- cate the lymph node indirectly. An open dissection is then performed over the area of interest. With this technique, second-order nodes are also detected, which can increase the invasiveness of the approach. 14 In human patients with breast cancer, spread from the tumor to the axillary lymph node is an important predictor for survival and recurrence. 15 Sentinel lymph node biopsy allows accurate staging of human patients with invasive breast cancer. 16 If a patient is negative for metastasis by sentinel lymph node biopsy, then radical axillary lymph node dissection can be avoided, which reduces morbidity. 17 To our knowledge, there are no published reports of mam- mary gland sentinel lymph node detection and biopsy using contrast-ultrasound guidance in dogs or people. Our objectives of this feasibility study were to evaluate a means of identifying the mammary sentinel lymph nodes in normal dogs using contrast-ultrasound imaging and to ob- tain representative samples of the sentinel lymph node un- der ultrasound guidance using a new handheld, vacuum- assisted biopsy device. Materials and Methods Before beginning the study, a phantom was used to en- sure the user acquired and demonstrated the ability to Supported by a grant from the Hologic Inc., Indianapolis, IN. Presented at the American College of Veterinary Radiology Annual Scientific Meeting, October 2009, Memphis, TN. Address correspondence and reprint requests to Dr. Lynetta J. Free- man, at the above address. E-mail: ljfreema@purdue.edu Received March 2, 2010; accepted for publication April 17, 2010. doi: 10.1111/j.1740-8261.2010.01712.x From the Department of Veterinary Clinical Sciences, Purdue University (Gelb, Rohleder), the Department of Veterinary Clinical Sciences (Free- man), and the Department of Comparative Pathobiology (Snyder), Purdue University School of Veterinary Medicine, West Lafayette, IN 47907, USA. 628