Synovial myxoma in the vertebral column of a dog: MRI description and surgical removal.

A 12 yr old castrated male mixed-breed dog presented with a 2 wk history of progressive tetraparesis. Neurologic deficits included a short-strided choppy gait in the thoracic limbs and a long-strided proprioceptive ataxia in the pelvic limbs. Withdrawal reflexes were decreased bilaterally in the thoracic limbs. Signs were consistent with a myelopathy of the caudal cervical/cranial thoracic spinal cord (i.e., the sixth cervical [C] vertebra to the second thoracic [T] vertebra). A mass associated with the C6-C7 articular facet on the left side was identified on MRI of the cervical spinal cord. The lesion was hyperintense to spinal cord parenchyma on T2-weighted images, hypointense on T1-weighted images, and there was strong homogenous contrast enhancement. Significant spinal cord compression was associated with the lesion. The mass was removed through a C6-C7 dorsal laminectomy and facetectomy. Histopathology of the mass was consistent with a synovial myxoma of the articular facet. A postoperative MRI showed complete surgical resection. Albeit rare, synovial myxomas should be included in the list of differential diagnoses for neoplasms affecting the vertebral columns in dogs.