Today’s case is a 13-year-old Fox terrier with increased respiratory rate on excitement or in lateral recumbency. What are your findings?
On both lateral projections, there is increased soft tissue opacity in the cranial thorax, cranial to the hilus of the lungs and projecting dorsal to it on the left lateral projection. On the dorsoventral projection, the mass is located more in the left hemithorax and displaces the trachea to the right. The vasculature to the cranial lung lobes appears small, and the left caudal lobar arteries and veins are less visible than the right. In the portion of the abdomen included, the liver is enlarged. There is a diffuse bronchointerstitial pattern throughout the lungs. In the portion of the abdomen included, the liver is enlarged.
Differential diagnoses for the origin of the thoracic mass include the left cranial lung lobe, the mediastinum, or less likely the thoracic wall. The central location of the mass on both lateral projections suggests a dorsal mediastinal origin, however this should be confirmed with thoracic ultrasonography or echocardiography. The location is less typical of a ventral mediastinal mass such as thymoma. The small pulmonary vessels may suggest compression of the pulmonary artery by the mass. The diffuse bronchointerstitial pattern may be inflammatory or fibrotic in nature.
Thoracic ultrasonography and echocardiography were performed and the mass was seen to originate in the region of the aortic arch and surrounded the main pulmonary artery. A fine needle aspirate was non-diagnostic. Differential diagnoses included chemodectoma and ectopic thyroid carcinoma.