Imaging investigation of the axial skeleton in small animals is not an easy task. One of the most important factors is the positioning of the radiographs. Any obliquity of the radiograph may produce false lesions or make the diagnosis impossible. As a general rule, most animals need to be heavily sedated or under general anesthesia for optimal positioning. Radiography of non-sedated and non-anesthetized patients may rule out any obvious fractures of the vertebrae. Small fractures of the skull may not be seen on improperly positioned radiographs.

Just like any other region of the body, a minimum of 2 orthogonal views is required for the evaluation of the axial skeleton. Additional oblique images are required for the skull, especially in the investigation of the mandible or tooth lesions. This is also true for the myelography procedure. Oblique radiographs will be needed to determine the side of the lesion. The lateral and VD/DV alone will not be able to localize the lesion. Thus the labeling of the images is very important to avoid confusion with the oblique view and localization of the lesion.

One of the most common indicators for axial skeletal radiology is traumatic fracture of the skull or the vertebrae. It is difficult to detect a small fracture of the skull. A good physical examination is required to locate the possible fracture site. A combination of multiple oblique views is normally required to produce diagnostic radiographs.

For the investigation of a suspected vertebral fracture, a lateral radiograph of the vertebrae should be the initial step. Care must be taken in the positioning to avoid any further compression of a possible spinal cord lesion. Once the diagnosis is made, then careful positioning for the VD/DV should be performed. This is to investigate for the lateral subluxation or luxation of the vertebral column. Due to many superimposition structures in both the skull and the vertebral column, computed tomography is preferred if it is available.¹ This modality will provide a better cross-sectional view of the region of interest, and thus overcome the problem of superimposition.

Spondylosis deformans and diffuse idiopathic skeletal hyperostosis (DISH) in dogs are normally benign degenerative changes of the vertebral column without any clinical signs.² Spondylosis deformans is commonly present in the thoracolumbar and lumbosacral joints. DISH is a more severe bone proliferation of spondylosis deformans. The bone proliferation is located along the ventral longitudinal ligament and usually results in the formation of continuous bone of at least 4 contiguous vertebral bodies and preservation of the intervertebral disc spaces. If there are any clinical signs of the spinal column, then lesions in the adjacent segment of the vertebrae should be suspected.

Discospondylitis is an important disease that private practitioners should be able to diagnose on the routine spinal radiography. This is an infection of the disc and adjacent vertebral endplates, usually due to hematogenous route of bacteria or fungal infection. The hallmark radiographic sign of discospondylitis is endplate lysis of adjacent vertebral bodies with collapse of the intervertebral disc space. The radiographic lesion normally appears 2 or 4 weeks after the onset of clinical signs, and it continues to deteriorate despite successful treatment and diminished clinical signs. A lag of 3–9 weeks was seen between the improvement of clinical signs and radiographic appearance of the lesion.³

Spondylitis by definition is the inflammation of the body of the vertebra with or without infectious agents. Infectious spondylitis is normally associated with migrating inhaled grass awns or penetrating foreign bodies involving the mid-lumbar vertebra.⁴ Mid-thoracic vertebral spondylitis is commonly associated with spirocercosis.⁵ This lesion should be differentiating from vertebral neoplasia.

Primary and metastatic neoplasia of the vertebrae occurs commonly in small animals. Primary neoplasia could occur in any vertebra, and it could be either osteolytic, osteoblastic or a mixed appearance. It is more difficult to detect osteolytic lesions, thus careful evaluation of the vertebra, especially paying specific attention to the dorsal aspect of the vertebral body, is warranted. The subtle absence of the radiopaque line of the dorsal aspect of the vertebral body indicates osteolysis of the vertebral body.

Metastatic neoplasia of the vertebra produces a nearly similar radiographic appearance to primary neoplasia of the vertebra. One unique radiographic feature of metastatic neoplasia of transitional cell carcinoma of the urinary bladder, prostatic neoplasia and anal gland adenocarcinoma is the smooth periosteal reaction at the ventral aspect of the vertebral body of the caudal lumbar (L5, L6 and L7).

References

1.  Kinns J, Mai W, Swingenberger A, Johnson V, Caceres A, Valdes-Martinez A, Schwarz T. Radiographic sensitivity and negative predictive value for acute canine spinal trauma. Vet Radiol Ultrasound. 2006;47:563–570.

2.  Ortega M, Goncalves R, Haley A, Wessman A, Penderis J. Spondylosis deformans and diffuse idiopathic skeletal hyperostosis (DISH) resulting in adjacent segment disease. Vet Radiol Ultrasound. 2012;53:128–134.

3.  Shamir MH, Tavor N, Aizenberg T. Radiographic findings during recovery from discospondylitis. Vet Radiol Ultrasound. 2001;42:496–503.

4.  Johnson DE, Summers BA. Osteomyelitis of the lumbar vertebrae in dogs caused by grass-seed foreign bodies. Aust Vet J. 1971;47:289–294.

5.  Kirberger RM, Cliff SJ, Wilpe EV, Dvir E. Spirocerca lupi-associated vertebral changes: a radiologic-pathologic study. Vet Parasitol. 2013;195:87–94.