When thoracic radiographs show an enlarged right heart and tortuous vessels, what is the likely diagnosis?

The presence of an enlarged right heart and tortuous vessels on thoracic radiographs is suggestive of heartworm disease. In this condition, the heartworm parasites reside within the pulmonary arteries, leading to inflammation and obstruction. This can increase the load on the right side of the heart, resulting in right ventricular hypertrophy and eventual right heart enlargement. Additionally, the tortuous appearance of the vessels can be attributed to the changes in the pulmonary arteries themselves, which may become distorted due to increased pressure and the presence of the parasites.

Other conditions, such as chronic bronchitis and canine dilated cardiomyopathy, can have their own specific radiographic findings but typically do not produce the characteristic combination of right heart enlargement and tortuous pulmonary vessels seen in heartworm disease. Similarly, while pulmonary hypertension can cause right heart enlargement, it is often secondary to other conditions rather than solely due to heartworm involvement. In this scenario, the specific interpretation of the radiographs aligns most clearly with heartworm disease as the primary concern.