Looks Like Cancer, But Isn’t: Rare Salivary Hyperplasia Mimics Metastasis in Dog

Retropharyngeal salivary adenomatous hyperplasia mimicking tumor metastasis in a dog

Jeongyun Jeong, Minjoo Kim, Jaehwan Kim, Kidong Eom

Background
Salivary adenomatous hyperplasia (SAH) is a rare, benign proliferation of salivary tissue, previously reported in other organs in veterinary species but not in the canine salivary system. This report describes the first case of SAH in a dog mimicking metastatic disease. Given its imaging similarity to malignancies, especially in patients with a history of cancer, SAH may be misdiagnosed without histopathology.

Methods
A 13-year-old castrated male poodle with previous right thyroid carcinoma and ipsilateral lymph node metastasis presented with respiratory distress and coughing. Initial suspicion was chronic bronchitis. Imaging (ultrasound and CT) identified a mass in the left medial retropharyngeal region. Given its heterogeneous enhancement and the dog's oncologic history, metastatic lymphadenopathy was suspected. Surgical excision was performed, and the mass was submitted for histopathological analysis.

Results
CT revealed an enlarged, heterogeneously enhancing mass compressing the laryngeal wall. The mass was well-encapsulated and surgically removed without complications. Histopathology showed mild salivary adenomatous hyperplasia with duct ectasia and no evidence of neoplasia or significant inflammation. The dog's clinical signs resolved postoperatively, confirming the mass's role in the respiratory symptoms.

Limitations
Fine-needle aspiration was avoided due to anatomical concerns, delaying definitive diagnosis. The exact origin of the hyperplastic tissue (heterotopic, minor, or accessory salivary gland) was unclear due to absence of typical glandular structures in histology. As a single case report, findings are not broadly generalizable.

Conclusions
This case demonstrates that SAH can clinically and radiographically mimic malignant disease, particularly in patients with prior cancer history. Despite its benign nature, SAH may cause significant clinical signs depending on size and location. Definitive diagnosis requires histopathology, and it should be considered as a differential in retropharyngeal or salivary region masses.

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