Thyroid carcinosarcoma masquerading as a paraesophageal abscess in a Cane Corso dog

A 12-year-old castrated male Cane Corso dog was presented with cervical swelling, lethargy, anorexia, and cough. An extensive neck mass with necrotic cysts was observed, severely adherent to surrounding tissues. Based on diagnostic imaging including ultrasound, computed tomography, and fine-needle aspiration cytology, paraesophageal abscess was tentatively diagnosed. However, after the mass was surgically removed, a diagnosis of thyroid carcinosarcoma composed of neoplastic cell populations with epithelial and mesenchymal origins was made via histopathology and immunohistochemistry. The dog died of a recurrent mass with pulmonary metastasis 105 d after surgery. This report describes a rare type of canine thyroid cancer, thyroid carcinosarcoma, preoperatively masquerading as an abscess and postoperatively confirmed by histopathology. Key clinical message: Thyroid carcinosarcoma, despite its rarity in dogs, should be included in the differential diagnoses of cervical mass especially with an aggressive progression.