Mediastinal Paraganglioma as a Cause of Hemothorax and Thoracic Spinal Cord Compression in a Quarter Horse Gelding

Neuroendocrine tumors are rarely diagnosed in horses. This report describes a case of a neuroendocrine tumor with strong similarities to descriptions of posterior mediastinal paragangliomas in humans and dogs. A 12-year-old Quarter Horse gelding was presented initially for management of hemothorax of unknown origin that responded to medical management. Nineteen months later, the horse was presented again with acute-onset hindlimb ataxia, at which time a thoracic mass adjacent to the vertebral bodies was detected on radiography. The gelding was euthanized after failing to respond to anti-inflammatory therapy, and on necropsy, the mass was identified as a paraganglioma invading the spinal canal. Despite its locally invasive behavior, the tumor showed no evidence of metastasis, and its apparent slow progression was in sharp contrast to more common thoracic neoplasms such as hemangiosarcoma. Combined with the reported success of surgical excision in human mediastinal paragangliomas, this suggests that early diagnosis of such tumors could provide the opportunity for successful treatment.