Establishing Marginal Lymph Node Ultrasonographic Characteristics in Healthy Bottlenose Dolphins (Tursiops truncatus)
Pulmonary disease has been well documented in both wild and managed dolphin populations.1-4 Thoracic ultrasound has become a valuable diagnostic tool, allowing for prompt detection of peripheral pulmonary disease in cetaceans.5,6 Ultrasonographic evaluation of the thoracic lymph nodes has not been reported in cetaceans. The marginal lymph nodes of the dolphin thorax are of special interest because they provide lymphatic drainage to the lungs and can indicate pulmonary disease.5,7 The purpose of this study was to standardize a technique for efficient and thorough ultrasonographic evaluation of the marginal lymph nodes in bottlenose dolphins (Tursiops truncatus).
Thoracic ultrasonography was performed on 29 clinically healthy bottlenose dolphins at SeaWorld of California, San Diego, CA, USA and the United States Navy Marine Mammal Program in San Diego, CA, USA. Data variables were identified for various transducer orientations including: longitudinal, transverse, oblique, and an orientation optimized to the ultrasonographer's eye. Reference intervals and sonographic characteristics of normal marginal lymph nodes in healthy adult dolphins were determined. The relationship between the lymph node dimensions and age, gender, dolphin length, weight, morphotype, and management setting (above-ground pools versus open ocean enclosures) were also evaluated. The mean marginal lymph node dimensions were 5.26 cm for length (SD = 1.10 cm, min = 3.04 cm, max = 7.61 cm, reference interval = 3.78–6.55 cm) and 3.72 cm for width (SD = 0.59 cm, min = 2.64, max = 5.38 cm, reference interval 2.98–4.50 cm). Dolphins in the oldest age group (> 30 years) had longer lymph node lengths than those in the youngest age group (5–10 years old). No effect of gender, dolphin length, weight and management setting were found. The offshore dolphin morphotype were found to have smaller lymph node lengths when compared to the coastal form. This may be attributed to the larger lung tidal volume previously established in the offshore morphotype,8 contributing to the inability to fully evaluate the lymph node due to the larger field of air-associated acoustic shadowing. Marginal lymph node ultrasonographic characteristics varied greatly. Most commonly the node was found to be hyperechoic to surrounding tissues (98%), moderately heterogeneous (34%), to have a flat superficial border (67%), a triangular or rounded triangular shape (59%), ill-defined deep borders (84%), and irregular cranial (55%) and caudal borders (84%). A rapid and effective transthoracic ultrasound technique of the marginal lymph node in bottlenose dolphins was established. The ultrasound data reported in this study may serve as a baseline reference which may contribute to earlier detection of pleural and pulmonary disease of managed and wild cetacean populations.
The authors wish to thank our colleagues at SeaWorld California, the U.S. Navy Marine Mammal Program, and the National Marine Mammal Foundation. We are grateful for the numerous veterinary technicians, trainers, and support staff that have aided with the study.
* Presenting author
+ Student presenter
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