Magnetic Resonance Imaging Diagnosis of Intervertebral Disc Disease and Myelomalacia in an American Black Bear (Ursus americanus)
A 23-year-old black bear (Ursus americanus) was examined because of paralysis. The onset of clinical signs was unknown due to seasonal torpor. An observational exam confirmed the absence of motor function in the pelvic limbs and normal thoracic limb function. The bear was immobilized using hydromorphone (Baxter Healthcare, Deerfield, Illinois 60015 USA; 0.08 mg/kg IM) and tiletamine/zolazepam (Telazol®, Fort Dodge Laboratories, Inc., Fort Dodge, Iowa 50501 USA; 4 mg/kg IM) for further evaluation. Radiography revealed increased mineral opacity and ventral bridging across vertebral segments T8–T11. Magnetic resonance imaging revealed a focal hypointense, extradural lesion dorsal to the cord at the T8–T9 intervertebral disc space on sagittal and transverse T2-weighted (T2W) images. The transverse images confirmed cord compression associated with the mass. A mildly ventrally compressive lesion also was seen at this level, hypointense to the cord on T1-weighted (T1W) and T2W images. This was compatible with herniated disc material and suggested that the dorsal lesion may have also been extruded disc in an unusual location. Based on these findings, along with the bear’s advanced age, euthanasia was elected. Necropsy exam revealed ankylosing spondylosis from T7–L3 and dorsal extradural extruded disc material in the area of T8–T9. Histopathology demonstrated the dorsal horns of the affected cord were replaced by foamy macrophages extending into the white matter compatible with focal, severe, chronic myelomalacia. This is the first report of intervertebral disc herniation in an ursid and the first report demonstrating the use of MRI to diagnose IVDD in any large carnivore.1-4
The authors would like to thank Berkley Boone and the Athens-Clarke County Department of Leisure for their willingness to pursue a complete work-up and for their excellent care of this bear while she was in their charge. The authors would also like to gratefully acknowledge the University of Georgia Bio-Imaging Research Center for donation of MRI time and Kim Mason for her MRI technical assistance.
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