Retropharyngeal salivary adenomatous hyperplasia mimicking tumor metastasis in a dog.

This report describes the case of a 13-year-old castrated male poodle with respiratory distress and coughing. The dog had had its right thyroid gland and ipsilateral lymph node resected because of thyroid follicular carcinoma originating in the right thyroid gland and metastasis to the ipsilateral medial retropharyngeal lymph node. The dog was initially treated for chronic bronchitis but showed no resolution of the clinical signs. Ultrasonography revealed an enlarged hypoechoic left medial retropharyngeal mass. Computed tomography further revealed an enlarged, heterogeneously enhanced left medial retropharyngeal mass with irregular margins. The mass compressed the laryngeal borders and was considered responsible for the coughing and respiratory distress. Based on the dog's history of thyroid carcinoma, metastatic lymphadenopathy of the left medial retropharyngeal lymph node was suspected, and the mass was surgically removed. Histopathologic examination revealed mild adenomatous salivary hyperplasia with duct ectasia. No evidence of neoplasm or severe inflammation was observed. The final diagnosis was salivary adenomatous hyperplasia in the retropharyngeal region. Salivary adenomatous hyperplasia can be responsible for clinical signs, depending on size and location. Differentiating salivary adenomatous hyperplasia from malignancies based on imaging findings alone can be difficult. This case demonstrated how salivary adenomatous hyperplasia may mimic malignant tumors, particularly in animals with a history of adjacent tumor malignancy. Key clinical message: To the best of our knowledge, this is the first report in a dog of salivary adenomatous hyperplasia that mimicked tumor metastasis. Differentiating between malignant and salivary adenomatous hyperplasia can be difficult using imaging findings alone. Despite being histologically benign, salivary adenomatous hyperplasia may cause clinical signs.