Acute necrotizing myelopathy from nucleus pulposus embolism in dogs with intervertebral disk degeneration

Two dogs that suddenly developed neurologic signs indicating a severe cervical spinal cord lesion were found at necropsy to have necrotizing myelopathy secondary to nucleus pulposus embolism. One dog had embolism of arteries and veins; in the other dog, veins alone were embolized. Each dog had early degeneration and extrusion of the C6--7 disk, from which emboli originated. In one dog, arterial emboli apparently entered inflammatory vasculature in the anulus fibrosus and were forced by extrusion back through the arterial system to the radicular artery and then to the cord. Venous embolism occurred secondarily to arterial embolism. In the other dog, venous embolism resulted from direct herniation of nucleus pulposus into the longitudinal venous sinus. A comparison of the pathogenesis of embolization in each case and a survey of other reported cases suggested that necrotizing myelopathy is a complication of early degeneration of intervertebral disks in large dogs.