Abstract

Abnormalities of the oral mucosa are a common clinical finding in wild and managed populations of bottlenose dolphins.¹ Early changes may appear as small proliferative and/or ulcerative lesions which may affect the lingual, sublingual and oropharyngeal mucosa. It has been suggested that these benign lesions undergo malignant transformation to squamous cell carcinoma (SCC), similar to viral induced neoplasms in other species.² However, although both papilloma and herpes viruses have been isolated from these lesions, a direct causal link has not been established.³

A variety of treatment modalities have been utilized to address the benign and neoplastic lesions.⁴ Recently, oral piroxicam has been anecdotally reported to stabilize oral SCC in some cetaceans.⁵ In one case report, the concurrent use of piroxicam and doxycycline lead to the resolution of a non-resectable tumor in the oropharynx of a Tursiops aduncus.⁶ However, the most common treatment of choice continues to be surgical excision of the tumor.

In 2004, a 31-year-old male Atlantic bottlenose dolphin (Tursiops truncatus) was diagnosed with oral SCC. Excisional biopsies using local anesthesia were performed to treat the original lesions. Subsequently, new papillomatous nodules or areas of persistent ulceration were managed with cryosurgery. However, in 2017, fine needle aspirates were obtained from three sub-mucosal nodular masses in the sublingual area. SCC was confirmed or suspected in all samples and surgical resection was recommended.

A combination of sedation and local anesthesia has commonly been used to facilitate the removal of both small and very large oral SCC tumors in dolphins. However, in recent years general anesthesia has been increasingly utilized to facilitate a variety of surgical procedures in cetaceans.^7-10 General anesthesia provides several benefits for oral surgery, including having a completely immobile patient who is pain free throughout the procedure. As with all anesthesia cases, patient factors such general physical condition and concurrent health issues should be considered to determine if the patient is a good candidate for general anesthesia and to address potential intra- and post-operative complications.

Although he was 44 years old, this dolphin was in overall good health and was therefore determined to be a good candidate for general anesthesia. He received oral diazepam 2 hours prior to the start of the procedure and an intramuscular injection of midazolam at the time he was removed from the water. Once in the surgical room, a catheter was placed in the left lateral subcutaneous caudal vein. General anesthesia was induced with propofol and was maintained with sevoflurane. Surgical excision of the 3 sublingual masses and a 1 cm oropharyngeal nodule was performed. Local anesthesia was achieved with lidocaine prior to the start of surgery and bupivacaine was administered at the end of the procedure. Total surgery time was 2 hours and recovery was uneventful.

In the event that a large resection is warranted to address an oral SCC, general anesthesia should be considered if the patient is determined to be in good physiological condition. To the authors’ knowledge he is the oldest dolphin to have successfully undergone general anesthesia.⁷

Acknowledgements

The authors would like to thank Todd Schmitt for sharing his experiences with dolphin anesthesia, and Carolina Le-Bert and Shawn Johnson for their technical assistance during the procedure. Thank you to the National Marine Mammal Foundation/Navy Marine Mammal Program and The Marine Mammal Center for supporting Dr. Le-Bert and Dr. Johnson, respectively. Finally, special thanks to our surgeons Philip Browning and Jolene Bachman and the Animal Care staff at SLPH.

* Presenting author

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