Case Study 1 (Page 1)

Patient History: A 10 year 6 month old dachshund was presented to the Veterinary Neurological Center for evaluation of episodic neck pain and progressive difficulty using the left thoracic limb for the past 2 months. The patient had shown brief periods of transient improvement with cage rest and administration of Rimadyl® and occasional tramadol.

Question: Based on this radiograph and the presenting signs, where would the problem most likely be localized?

Imaging Findings: The radiograph shows a congenital fusion of the C3 and C4 vertebrae, i.e., a block vertebra.

Discussion: The block vertebra could result in a lack of normal range of motion of the cervical vertebrae causing extra stress on the C2-3 and C4-5 disk spaces. This stress could lead to an intervertebral disk extrusion. Other differentials include infectious or inflammatory disease or neoplasia.

Question: Based on this assessment, what next step would be best to find the problem?

Discussion: CT, conventional myelography, or CT myelography could have been helpful in diagnosing this dog's problem. MRI was chosen over CT in this case because of the lack of radiographic evidence of calcified intervertebral disks. A non-calcified disk herniation would not have been well visualized on CT (see CT vs MRI). A CT myelogram would likely have shown the lesion but is more invasive and shows less detail than MRI. Conservative management in patients with disk herniations is generally unrewarding.

The MRI revealed the following images (click to enlarge):

Question: Based on the previous findings and these MR images, what is the most likely cause of this patient's problem?