Abstract

A 15-yr-old aquarium-housed female Atlantic walrus (Odobenus rosmarus rosmarus) presented with a non-painful cervical enlargement that had progressed over a few months. Cervical ultrasound showed bilateral masses, located 2.5 to 5 cm from the skin surface and non-adherent to deep planes. These masses were composed of a cystic and vascularized glandular tissue, delineated by a well-demarcated capsule. Within 10 mo, the lesion’s size increased from 10 cm to greater than 25 cm in diameter. Repeated fine needle aspirations were inconclusive. Hematology and biochemistry were unremarkable. Total T4 concentrations (9.2 and 9.6 nmol/L) were markedly lower than values obtained in wild walruses (unpublished data). Serum TSH levels (IMMULITE®, Diagnostic Products Corporation, Los Angeles, CA, USA) of 7.51 ng/ml were markedly increased compared to values obtained in three other aquarium-housed walruses (0.06–1.01 ng/ml, n=7 samples). Hypothyroidism associated with hyperplastic thyroid glands was suspected. Nutritional factors including iodine and selenium intake were evaluated. Dietary modifications were implemented including a switch to a mineral supplement without iodine. Treatment with levothyroxine was initiated with follow-up TSH level measurements for dose adjustment. A maintenance dose of 0.02 mg/kg orally twice daily produced a reduction of TSH concentration to 0.27 ng/ml. Mass diameter decreased to 10 cm in diameter within 4 mo; however, hormonal factors or immunity modulation associated with pregnancy cannot be ruled out as this female was pregnant during treatment. Even if not reported in the scientific literature, this case, as well as anecdotal reports, suggests that thyroid hyperplastic lesions should be considered in the presence of cervical enlargement in this species.

Acknowledgments

The authors thank the team of veterinarians and veterinary residents, as well as animal care team and trainers from the Aquarium du Québec for their help with the management of this animal.