Canine intrapericardial extracardiac myxosarcoma causing pericardial effusion and tamponade.

A 1-year and 4-month-old neutered male shar-pei dog was brought to the emergency department for evaluation of pericardial effusion and a suspected cardiac mass. The presence of a mass with adhesions to the pericardium, right auricle, and right vzentricle was confirmed through computed tomography, thoracic radiography, and echocardiography. The mass was surgically excised and diagnosed through histopathology as a myxoma or low-grade myxosarcoma with mineralization and osseous metaplasia. This case report describes the diagnostic tests completed, the surgical excision, and the outcomes of a rare cardiac neoplasia in an uncommon location. Key clinical message: This report describes the clinical presentation, diagnosis, and surgical management of an intrapericardial extracardiac myxosarcoma in a dog with cardiac tamponade. This rare type of neoplasia should be considered as a differential diagnosis in dogs with intrapericardial masses. Surgical excision of these masses should be considered as a treatment option in applicable cases.