Abstract

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.

Acknowledgments

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

Literature Cited

1.  Bogomolni AL, Pugliares KR, Sharp SM, Patchett K, et al. Mortality trends of stranded marine mammals on Cape Cod and southeastern Massachusetts, USA, 2000 to 2006. Dis Aquat Org. 2010;88:143–155.

2.  Cornaglia E, Rebora L, Gilli C, Di Guardo G. Histopathological and immunohistochemical studies on cetaceans found stranded on the coast of Italy between 1990 and 1997. J Vet Med A Physiol Pathol Clin Med. 2000;47:129–142.

3.  Dunn JL, Buck JD, Robeck TR. Bacterial disease in cetaceans and pinnipeds. In: Dierauf LA, Gulland FMD, eds. CRC Handbook of Marine Mammal Medicine. 2nd ed. Boca Raton, FL: CRC Press; 2001:309–335.

4.  Venn-Wason S, Daniels R, Smith C. Thirty year retrospective evaluation of pneumonia in a bottlenose dolphin Tursiops truncatus population. Dis Aquat Org. 2012;99:237–242.

5.  Brook F, Van Bonn W, Jensen E. Ultrasonography. In: Dierauf LA, Gulland FMD, eds. CRC Handbook of Marine Mammal Medicine. 2nd ed. Boca Raton, FL: CRC Press; 2001:593–620.

6.  Smith CR, Solano M, Lutmerding BA, Johnson SP, Meegan JM, Le-Bert CR, Emory-Gomez F, Cassle S, Carlin K, Jensen ED. Pulmonary ultrasound findings in a bottlenose dolphin Tursiops truncatus population. Dis Aquat Org. 2012;101:243–255.

7.  Cowan DF, Smith TL. Morphology of the lymphoid organs of the bottlenose dolphin, Tursiops truncatus. J Anat. 1999;194:505–517.

8.  Ridgway SH. Diving by cetaceans. In: Brubakk AO, Kanwisher JW, Sudness G. Diving in Animals and Man. Trondheim, Norway: The Royal Norwegian Society of Science and Letters; 1986:33–62.