History
A 2-year-old spayed female Miniature Pinscher was referred for signs of pain in the cervical region characterized by ambulatory paraparesis progressing to nonambulatory paraparesis of 4 days' duration. Treatment by the referring veterinarian included enrofloxacin and meloxicam. Earlier on the day of evaluation, the dog was also given an injection of prednisone by the referring veterinarian. Ovariohysterectomy as treatment for pyometra had been performed 2 weeks prior to the onset of neurologic signs. The dog's vaccination status was adequate. It was infected with Dirofiliaria immitis. Treatment with monthly heartworm preventative had been initiated by the referring veterinarian at the time of ovariohysterectomy.
Right lateral (A) and ventrodorsal (B) myelographic views of the cranial cervical portion of the vertebral column in a 2-year-old Miniature Pinscher evaluated for signs of pain in the cervical region and neurologic deficits of 4 days' duration.
Citation: Journal of the American Veterinary Medical Association 230, 6; 10.2460/javma.230.6.821
Right lateral (A) and ventrodorsal (B) myelographic views of the cranial cervical portion of the vertebral column in a 2-year-old Miniature Pinscher evaluated for signs of pain in the cervical region and neurologic deficits of 4 days' duration.
Citation: Journal of the American Veterinary Medical Association 230, 6; 10.2460/javma.230.6.821
Right lateral (A) and ventrodorsal (B) myelographic views of the cranial cervical portion of the vertebral column in a 2-year-old Miniature Pinscher evaluated for signs of pain in the cervical region and neurologic deficits of 4 days' duration.
Citation: Journal of the American Veterinary Medical Association 230, 6; 10.2460/javma.230.6.821
On physical examination, the dog was tetraplegic and hyperreflexic in all 4 limbs. Signs of deep pain were detected in all limbs. Hyperpathia was detected from C2 through C4. A grade 3/6 heart murmur was also detected during auscultation of the thorax. Echocardiography was not performed because of financial constraints. Myelography of the cervical region was performed by slow injection of 1.5 mL of contrast mediuma at the atlanto-occipital junction into the cerebellomedullary cistern. The dog's head was elevated for approximately 1 minute, after which radiographs of the cervical portion of the vertebral column were obtained (Figure 1).
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Same myelographic views as in Figure 1. On the lateral myelographic view (A), notice subtle attenuation of the contrast material ventrally (single arrow) and dorsally (3 arrows). On the ventrodorsal myelographic view (B), notice deviation of contrast medium (arrow) indicating a left-sided extradural lesion.
Citation: Journal of the American Veterinary Medical Association 230, 6; 10.2460/javma.230.6.821
Same myelographic views as in Figure 1. On the lateral myelographic view (A), notice subtle attenuation of the contrast material ventrally (single arrow) and dorsally (3 arrows). On the ventrodorsal myelographic view (B), notice deviation of contrast medium (arrow) indicating a left-sided extradural lesion.
Citation: Journal of the American Veterinary Medical Association 230, 6; 10.2460/javma.230.6.821
Same myelographic views as in Figure 1. On the lateral myelographic view (A), notice subtle attenuation of the contrast material ventrally (single arrow) and dorsally (3 arrows). On the ventrodorsal myelographic view (B), notice deviation of contrast medium (arrow) indicating a left-sided extradural lesion.
Citation: Journal of the American Veterinary Medical Association 230, 6; 10.2460/javma.230.6.821
Radiographic Findings and Interpretation
On the lateral myelographic view, subtle loss of contrast medium is evident ventrally and dorsally at the C3 vertebral body (Figure 2). On the ventrodorsal myelographic view, a deviation of the contrast medium to the right is detected within the C3 vertebral body. The myelographic lesion is not located at the intervertebral disk space. These findings are consistent with an extradural left-sided compressive lesion.1 Differential diagnoses for extradural compressive lesions include intervertebral disk extrusions or protrusions, ligamentous hypertrophy, vertebral fractures and luxations, hematoma or hemorrhage, neoplasia (vertebral or epidural),1 granuloma, and subarachnoid cyst.2
Comments
Intervertebral disk extrusions or protrusions and ligamentous hypertrophy typically appear as extradural filling defects located over the intervertebral disk space, not over the body of a vertebra. Fractures and luxations of the vertebrae are typically bilateral and indicate spinal malalignment or discontinuity, which are not evident in this dog. The ventrodorsal myelographic view was important for localization of the lesion because few changes were detected on the right lateral myelographic view.
On the basis of the myelographic lesion, dorsal laminectomy of C3 was performed. On entrance to the vertebral canal, a collection of small nematodes, presumably D immitis, was detected. Aberrant migration of D immitis to the vertebral canal has been reported but appears to be extremely rare.3-5 In 1 report,3 D immitis was detected at C2 and C3, and in 2 reports,4,5 D immitis was detected in the thoracolumbar region. A number of theories regarding the mechanism of aberrant migration of D immitis to the epidural space have been proposed, including migration of mature nematodes from a blood vessel or, alternatively, migration of immature larvae to the vertebral foramen with subsequent molting and final migration of adult nematodes into the epidural space.5 However, to the authors' knowledge, studies concerning the mechanisms involved in aberrant migration of D immitis have not been published.
In the dog reported here, no complications were detected after myelography or after surgery. Five days after surgery, the dog was tetraparetic and weakly ambulatory and no longer had signs of cervical pain. Three months after surgery, the dog was mildly ataxic in the hind limbs but had no signs of cervical pain and had returned to its normal activity level.
Myelography is useful for evaluation of the spinal cord. For most spinal cord–related lesions, plain-film radiography is not adequate for localization of a lesion. Accuracy of plain-film radiography for identification of the site of disk extrusion in dogs with cervical intervertebral disk disease has been found to be only 35%6 and is presumed to be less in lesions involving only the soft tissue structures of the spinal cord and meninges. Myelography is indicated for investigation of spinal lesions that cannot be visualized by plain-film radiography alone,1 and it is particularly useful when accessibility or financial limitations preclude the use of computed tomography or magnetic resonance imaging.
Omnipaque, Amersham Health, Princeton, NJ.
- 1↑
Widmer WR. Intervertebral disk disease and myelography. In:Thrall DE, ed.Textbook of veterinary diagnostic radiology. 3rd ed. Philadelphia: WB Saunders Co, 1998;89–104.
- 2↑
Owens JM, Biery DN. Spine. In:Owens JM, Biery DN, ed.Radiographic interpretation for the small animal clinician. 2nd ed. Baltimore: The Williams & Wilkins Co, 1999;129–131.
- 3↑
Blass CE, Holmes RA, Neer TM. Recurring tetraparesis attributable to a heartworm in the epidural space of a dog. J Am Vet Med Assoc 1989;194:787–788.
- 4
Luttgen PJ, Crawley RR. Posterior paralysis caused by epidural dirofilariasis in a dog. J Am Anim Hosp Assoc 1981;17:57–59.
- 5↑
Shires PK, Turnwald GH, Qualls CW, et al. Epidural dirofilariasis causing paraparesis in a dog. J Am Vet Med Assoc 1982;180:1340–1343.
- 6↑
Somerville MS, Anderson SM, Gill PJ, et al. Accuracy of localization of cervical intervertebral disc extrusion or protrusion using survey radiography in dogs. J Am Anim Hosp Assoc 2001;37:563–572.
