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There is a large soft tissue opaque mass with irregular amorphous mineralization associated with the cranioventral thorax, silhouetting with the cranial cardiac margin and resulting in dorsal and caudal displacement of the carina. There is generalized increased soft tissue opacity to the ventral thorax, with a scalloped margin towards the dorsal lung fields. This opacity obscures the caudal margin of the heart and the ventral aspect of the diaphragm. A small amount of gas outlines the caudodorsal lung lobes. The lung lobes are retracted but no obvious pulmonary abnormalities are detected. A small amount of gas is noted within the thoracic esophagus. Thoracic drains are in place, and tubing material is superimposed over the cranioventral abdomen.
Cranioventral mediastinal mass, mostly of soft tissue opacity with evidence of dystrophic mineralization. In this species, thymoma is the primary differential diagnosis. Neoplastic lesions of a different etiology such as lymphoma or an inflammatory lesion such as a large granuloma cannot be excluded. Pleural effusion secondary to cranial mediastinal mass. Mild pneumothorax, likely secondary to placement of thoracic drains.
Ultrasound-guided fine needle aspiration or biopsy of the cranial mediastinal mass. Orthogonal views of the thorax could be considered but would likely not be possible in a patient of this size.
Comments on candidate performance:
Most candidates did poorly on this case. Many candidates mistook bilateral chest drains for metallic foreign bodies and jumped to a conclusion of traumatic reticuloperitonitis (Note: If candidates asked specifically if the patient had thoracic drains in place this information was provided). Most candidates identified increased opacity in the ventral thorax, but many failed to include pleural effusion in their list of differential diagnoses. Many candidates missed the cranial mediastinal mass entirely. Most candidates identified amorphous mineralization caudal to and overlying humeri and triceps musculature but erroneously interpreted it as mineralization within the forelimbs not noting that the position of the opacities changed in relation to the humeri on successive radiographs. Some candidates correctly identified a cranial mediastinal mass but attributed it to migration of foreign material secondary to traumatic reticuloperitonitis. Successful candidates identified the mineralized cranial mediastinal mass, pleural effusion and thoracic drains and listed the most likely differential diagnosis (thymoma) given the species.
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