Ectopic thyroid carcinoma causing right ventricular outflow tract obstruction in a dog.

Area of Science:

• Veterinary Cardiology
• Veterinary Oncology
• Comparative Pathology

Background:

• Intracardiac masses are uncommon in dogs and can lead to significant clinical signs.
• Ectopic thyroid carcinoma is a rare neoplasm that can occur in various locations.
• Chylous pleural effusion can be a sign of cardiac compromise or lymphatic obstruction.

Observation:

• A 9-year-old Bouvier des Flandres presented with coughing, lethargy, chylous pleural effusion, and a heart murmur.
• Echocardiography identified an intracardiac mass obstructing the right ventricular outflow tract.
• The mass was surgically excised using total inflow occlusion.

Findings:

• Histopathology and immunohistochemistry confirmed the intracardiac mass as ectopic thyroid carcinoma.
• The dog survived surgery but experienced nonresolving chylothorax.
• Euthanasia was performed 11 months post-diagnosis at the owner's request due to persistent chylothorax.

Implications:

• This case highlights the importance of considering rare differentials for intracardiac masses in dogs.
• Surgical intervention for intracardiac tumors can be technically challenging but feasible.
• Ectopic thyroid carcinoma, though rare, should be included in the differential diagnosis for canine cardiac masses and associated effusions.
• Long-term management of chylothorax secondary to cardiac compromise remains a clinical challenge.