Abstract

Oral squamous cell carcinoma (SCC) is the most frequently diagnosed malignant neoplasm of bottlenose dolphins (Tursiops truncatus).^1,2 The tumor’s biologic behavior is slowly progressive yet highly aggressive over time, with local invasion and potential for systemic metastasis.¹ At present, staging neoplastic disease in cetaceans is limited, however the superficial cervical lymph nodes (SCLN) hold promise for diagnostic imaging and sampling in dolphins due to their clinical accessibility.¹ In humans, ultrasound alone has been found to be an accurate, sensitive, and specific diagnostic tool for identifying cervical lymph node metastasis in patients with oral SCC, however, in dolphins ultrasonographic features for healthy and pathological SCLN are currently lacking.^3,4 The objectives of this study were to 1) establish normal SCLN ultrasonographic characteristics in clinically healthy bottlenose dolphins, and to 2) compare the newly established data to dolphins with confirmed oral SCC to establish potential indicators of metastasis and advance the clinical management. Twenty-one clinically healthy dolphins and 11 dolphins with a histologic diagnosis of oral SCC were included in the cervical ultrasonography study performed at two marine mammal care facilities. Two additional dolphins with malignant SCC SCLN postmortem data were included in the study to strengthen imaging conclusions. Lymph node ultrasound data was collected in longitudinal and transverse transducer orientations for the most prominent SCLN identified bilaterally in each dolphin. Maximum node dimensions and sonographic features were established in the healthy and SCC dolphin groups (n=42 and n=22 lymph nodes, respectively). The severity of oral SCC lesions and abnormal lymph nodes changes were each graded then compared. Normal dimension reference intervals were established from healthy dolphins; length 1.65–2.75 cm, width 0.84–1.90 cm, height 1.55–2.75 cm. Ultrasonographic features were highly conserved among healthy dolphins, appearing ovoid (86%, 36/42), homogenous (100%, 42/42), isoechoic to the diagonal masto-humeral muscle (83%, 35/42), smoothly marginated (95%, 40/42), with two lymph nodes most often identified bilaterally (range 1–4 lymph nodes). Dolphins with oral SCC had significantly larger lymph node dimensions when compared to the healthy animals (length, width, height; p<0.05) and were consistent with human sonographic features of malignancy;^3,4 appearing atypically shaped (59%, 13/22), heterogeneous (55%, 12/22), irregularly marginated (68%, 15/22), more numerous (2–3 lymph nodes identified), and possessed unique features such as hypoechoic protuberances or nodular appearance. The severity of oral SCC lesions correlated with the magnitude of SCLN abnormalities. However systemic metastasis was confirmed with a minor oral lesion following previous resection, thus time from SCC diagnosis was identified the most a valuable predictor for SCLN changes. In enlarged lymph nodes, the height measurement was typically the longest dimension, underscoring the importance of the transverse image view for complete SCLN examinations. Future lymph node sampling will confirm if ultrasound alone can be as accurate in diagnosing SCC metastasis in dolphins as in humans.³ The normal SCLN ultrasound criteria established in dolphins may serve as an important baseline reference, while the abnormal features described in the oral SCC population may indicate local spread, facilitating improved metastatic disease monitoring and advancing the management of neoplasia in dolphins.

Acknowledgments

The authors wish to thank their animal care specialist, veterinary, and technician colleagues for their support in conducting this study.

*Presenting author
+Student presenter

Literature Cited

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2.  Newman S. 2006. Marine mammal neoplasia: a review. Vet Pathol 43:865–880.

3.  Hodder SC, Evans RM, Patton DW, Silvester KC. 2000. Ultrasound and find needle aspiration cytology in the staging of neck lymph nodes in oral squamous cell carcinoma. Brit J Oral Max Surg 384:30–436.

4.  Ahuja AT, Ying M, Ho SY, Antonio G, Lee YP, King AD, Wong KT. 2008. Ultrasound of malignant cervical lymph nodes. Cancer Imaging 8:48–56.