Answers:

 

 

 

 

1) What is the most likely diagnosis, and what other differentials should be considered?
-given the radiographic appearance of a solitary lung mass with no evidence of lymphadenopathy, a primary lung tumor (pulmonary carcinoma) is the top differential. Other etiologies to consider include other primary lung tumors such as histiocytic sarcoma, metastatic disease, fungal granuloma, abscess.

2) What additional diagnostics should be considered?
-a CT scan of the thorax and abdomen is appropriate for staging a suspected primary lung tumor. Aspiration cytology of the lesion is beneficial to help refine the diagnosis. 

3) Assuming there is no evidence of metastatic disease, what is the treatment of choice for a primary lung tumor?
-en bloc surgical excision via thoracotomy is the treatment of choice for primary lung tumors. Chemotherapy may have a role in the treatment of tumors with a more aggressive histology, although this role is not clearly defined. 

In this particular case the CT scan did not show any evidence of metastasis. Cytology of the mass was consistent with carcinoma. Therefore, the dog was taken to surgery via a lateral thoracotomy approach. The accessory lung lobe was removed with en bloc excision and the tissue was submitted for histopathology. Histopathology results demonstrated a grade II pulmonary adenocarcinoma with complete excision and no evidence of vascular or lymphatic invasion. Outcomes are typically good to excellent in cases like this, although grade III tumors have a higher metastatic rate.