Ectopic medullary (C cell) thyroid carcinoma in a dog with pericardial effusion

A six-year-old, female, neutered crossbreed was presented to the University of Liverpool Small Animal Teaching Hospital for evaluation of pericardial effusion. Diagnostic imaging confirmed pericardial effusion and cardiac tamponade in addition to a mass located at the heart base. Thoracic CT revealed a strongly contrast-enhancing soft-tissue mass right lateral to the ascending aorta and ventral to the cranial vena cava with no evidence of metastatic disease. Subsequently, a subtotal pericardectomy was performed, and the mass was incompletely excised. Histopathology and immunohistochemistry revealed the mass to be an ectopic thyroid carcinoma of medullary (C cell) origin. The patient was treated with adjunctive chemotherapy (toceranib phosphate). Repeat staging two months later revealed no evidence of macroscopic tumour recurrence or metastatic disease. The patient was subsequently euthanased two months later due to complications of concurrent but unrelated hepatic disease.