History
An 8-year-old spayed female mixed-breed dog was referred to the neurology service because of a 1-month history of progressive hind limb weakness and ataxia. The referring veterinarian had treated the dog with carprofen,a which resulted in a minimal transitory response followed by worsening of the clinical signs. Neurologic examination at the time of referral revealed complete paralysis in the hind limbs, no evidence of conscious proprioception in the hind limbs, and normal spinal reflexes in the caudal region. Signs of mild discomfort were elicited on palpation of the thoracolumbar junction. These findings were consistent with a T3-L3 myelopathy.
The dog was anesthetized to obtain survey radiographic views of the thoracolumbar area, which were deemed within normal limits. Myelography was performed following injection of contrast medium in the subarachnoid space at the L5-6 space (Figure 1).
Right lateral (A) and ventrodorsal (B) myelographic views of the caudal cervical and cranial thoracic portions of the vertebral column of a paralyzed 8-year-old spayed female mixed-breed dog.
Citation: Journal of the American Veterinary Medical Association 230, 10; 10.2460/javma.230.10.1463
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
In the radiographic views, severe attenuation of the ventral, dorsal, and lateral contrast columns is centered over the body of T4 (Figure 2); on the ventrodorsal view, axial displacement of the left-sided contrast column is visible, indicating presence of a large extradural mass deviating the spinal cord to the right, dorsal to the body of T4 (Figure 2). On the ventrodorsal view, lysis of the left pedicle and body of T5 is also suspected.
Same myelographic views as in Figure 1. A—Notice attenuation of the ventral and dorsal contrast columns centered over the body of T4 (asterisk). B—Notice attenuation of the right and left contrast columns dorsal to the body of T4, with deviation of the spinal cord to the right (black arrowhead) and lysis of the left pedicle and body of T4 (white arrowhead).
Citation: Journal of the American Veterinary Medical Association 230, 10; 10.2460/javma.230.10.1463
Postmyelographic computed tomography (CT) was performed to confirm the presence of an extradural mass and assess the degree of vertebral lysis. A large expansile mass of predominant soft tissue density causing severe lysis of the left aspect of the T4 vertebral body, pedicle, and lamina is evident (Figure 3). The spinal cord is severely compressed and displaced to the right. Computed tomography documented that the lytic and expansile changes were limited to the T4 vertebra. A diagnosis of primary bone tumor was considered most likely on the basis of the myelographic and tomographic features.
Postmyelography CT scan at the level of T4, displayed in a bone window (window width, 1,250 Hounsfield units; window level, 240 Hounsfield units). Notice a left-sided soft tissue mass that compresses the spinal cord to the right of the canal (arrowhead). Severe destruction of the vertebral body (asterisk), lamina, and pedicle is evident.
Citation: Journal of the American Veterinary Medical Association 230, 10; 10.2460/javma.230.10.1463
Comments
Immediately after the CT scan, a CT-guided fine-needle aspirate of the mass was obtained, yielding a cytologic diagnosis of osteosarcoma. Only a quarter of the osteosarcomas in dogs develop in the axial skeleton.1 The history of slowly progressive weakness of the hind limbs in a middle-aged dog puts neoplasia higher on the list of differential diagnoses; however, because of the nonspecific nature of these clinical signs, other differential diagnoses, such as intervertebral disk disease, fracture-luxation, myelitis, or degenerative myelopathy, needed to be ruled out.2 Diskospondylitis and meningitis, although possible causes of weakness and pain, do not typically induce neurologic signs.3 In this particular case, survey radiography was inconclusive as to the cause of the neurologic deficits. Even on retrospective evaluation of the survey radiographs, it was difficult to identify any evidence of bony lysis because of the overlying cardiac shadow on the ventrodorsal view and because of the fact that the survey radiographs of the cranial thoracic portion of the vertebral column were mildly underexposed. The task of making a definitive diagnosis of vertebral disease with survey radiography is often complicated by such factors as the inconsistency of vertebral shape, overlying rib and soft tissue shadows, and improper positioning techniques.2 Deviation of the spinal cord and the attenuation of the contrast column over the area of T4 during myelography led to a diagnosis of an extradural lesion compressing the spinal cord. Because bony lysis was suspected on myelography, making primary or metastatic bone tumor a likely diagnosis, CT was recommended and was key in revealing the dramatic degree of vertebral lysis and the large size of the mass. Computed tomography has many advantages in the detection of lesions because it can eliminate the superimposition of structures. In addition, the image can be displayed in various gray scale formats that allow better enhancement of the structures of interest. It also allows for reconstruction of the image in multiple anatomic planes.4
In the dog of this report, the owner chose medical management, and the dog was released and lost to follow-up evaluation.
Rimadyl, Pfizer Animal Health, Exton, Pa.
References
- 2↑
Morgan JP, Ackerman N, Bailey CS, et al. Vertebral tumors in the dog: a clinical, radiologic, and pathologic study of 61 primary and secondary lesions. Vet Radiol 1980;21:197–212.
- 3↑
LeCouteur RA, Grandy JL. Diseases of the spinal cord. In:Ettinger SJ, Feldman EC, ed.Textbook of veterinary internal medicine. 5th ed.St Louis: Elsevier Saunders, 2005;842–887.
- 4↑
Drost WT, Love NE, Berry CR. Comparison of radiography, myelography and computed tomography for the evaluation of canine vertebral and spinal cord tumors in sixteen dogs. Vet Radiol Ultrasound 1996;37:28–33.
