Clinical features and imaging findings for a mediastinal hemangiosarcoma in a dog.

An 8-year-old neutered male mixed-breed dog weighing 29.7 kg was presented because of peracute restlessness. Abdominal radiographs revealed mild gastric gas dilation. Thoracic radiographs demonstrated a mild caudodorsal mediastinal mass effect with moderate cranial mediastinal widening and mild accompanying pleural effusion. Pleural fluid cytology was consistent with hemorrhage (packed cell volume: 58%). Computed tomography revealed findings consistent with active pancreatitis and a noninvasive, pre-contrast hyperattenuating, non-enhancing caudodorsal mediastinal mass suggestive of an acute hematoma of unknown etiology. The dog was discharged for supportive care of pancreatitis and the mediastinal lesion was monitored. One month later, the dog was presented for a follow-up computed tomographic reevaluation. A persistent caudodorsal mediastinal mass with findings suggestive of an acute or chronic hematoma was appreciable. A newly noted nodular lesion in close association with the presumed hematoma became evident. In addition, new multifocal pulmonary nodules were visualized. Both findings were concerning for a caudodorsal mediastinal neoplasia with ongoing hemorrhage and pulmonary metastasis. The owners elected for supportive care without further diagnostic tests. The dog was presented again 3 wk later because of restlessness and a newly observed, rapidly growing subcutaneous mass that ultimately led to the decision for humane euthanasia. Histopathology of the caudodorsal mediastinal mass was consistent with hemangiosarcoma. This is a unique case report of a primary caudodorsal mediastinal hemangiosarcoma in which the initial diagnostic imaging only revealed a secondary hematoma, and the primary neoplastic lesion eventually became evident on a recheck imaging study. Key clinical message: Primary hemangiosarcoma should be considered as a differential diagnosis for a caudal mediastinal hematoma. Furthermore, given the progression of findings in this case, follow-up imaging is recommended in cases in which a cause of a mediastinal hemorrhage or hematoma is not identified with initial imaging.