Non-Invasive Assessment of Sentinel Lymph Nodes That Drain the Tumoral Mammary Glands in Female Dog

Introduction: Mammary gland tumours occupy a significant place in the pathology of this species. Female dogs that are not spayed after their first heat cycle have a higher predisposition of developing mammary tumours. Most tumours metastasize at distance via the lymphatic system. In these conditions, the sentinel lymph nodes of the mammary glands must be assessed prior to surgical treatment. Aims: Considering the insufficient usage of non-invasive investigative methods of the sentinel lymph nodes, the aim of this study is to describe the sonographic anatomy of the lymph nodes that drain the mammary gland tumours in female dog. Materials and Methods: Twelve dog females presenting tumours of the cranial and caudal abdominal mammary glands (A1 and A2), inguinal mammary gland (I) and cranial thoracic mammary gland (T1) were examined (group I). In addition, a control group composed of eight dog females was used (group II). The axillary and superficial inguinal lymph nodes were evaluated using an algorithm composed of gray-scale ultrasound, Doppler technique, contrast enhanced ultrasound (CEUS) and real time elastography. Surgical excision of the sentinel lymph nodes was performed and samples for histopathological examination were taken. Results: The following ultrasonographic findings revealed on gray-scale examination were suspected for the metastatic infiltration: hypoechoic pattern, round shape, hillus absence and heterogenicity. Doppler technique showed an aberrant and mixed vascularisation of the lymph nodes, while the CEUS revealed incomplete enhancement of lymph nodes parenchyma. On real time elastography, the presence of blue areas in more than 50% from the lymph nodes parenchyma led us to conclude that the lymph node stiffness was caused by metastatic infiltration. Histopathological examination confirmed the presence of the metastatic infiltration in 97% of the examined lymph nodes. Conclusion: The algorithm composed of gray-scale ultrasound, Doppler technique, CEUS and real time elastography proved to be efficient in diagnosing the metastatic infiltration of sentinel lymph nodes of mammary gland. Further studies are needed to validate the proposed algorithm.