Magnetic resonance imaging findings of a metastatic chemodectoma in a dog.

A 6-year-old, male, Collie-cross was presented with a non-weight bearing right thoracic limb lameness, right m. deltoideus, m. infraspinatus and m. supraspinatus atrophy, and severe neck pain with spasm of the cervical epaxial muscles. MRI revealed complete destruction of the 5th and 6th cervical vertebral bodies with lateral extradural spinal cord compression at the level of the 4th and 5th cervical vertebrae. These lesions were very clearly demonstrated on magnetic resonance images, while only subtle changes were seen on survey radiographs. Post mortem investigation revealed a large heart base chemodectoma with multiple smaller tumours in the cranial mediastinum and a single tumour nodule on the thoracic aorta. The 5th cervical vertebral body had necrotic, haemorrhagic and lytic changes. Histopathology of the heart base tumour, the nodules in the cranial mediastinum and on the thoracic aorta and samples from the 5th cervical vertebra confirmed the presence of a malignant aortic or carotid body tumour originating from the chemoreceptor organs. Diagnostic imaging features and post mortem findings are described. To our knowledge, this is the first report of the magnetic resonance features of a metastatic chemodectoma in a dog.