Page 289 - Canine Lameness

16.3 ­Neurorogico giNciNi AANicgio ctNe trucigi gim 261

(A) (B)

(C) (D)

Figure 16.1 Imaging abnormalities illustrating a cervical fracture, radiographic changes of degenerative
intervertebral disc disease, and diffuse idiopathic skeletal hyperostosis (DISH): (A) lateral survey radiograph
illustrating a comminuted fracture of C2 with minimal displacement; (B) CT of same patient highlighting an
incomplete fracture through the cranial to mid-aspect of the left lamina of C2; (C) narrowed disc space,
sclerotic end plates, and spondylosis deformans at C6–C7 suggestive of degenerative disc disease; and (D)
classic radiographic appearance of DISH; note this condition generally does not cause clinical symptoms.

The imaging modality of choice in patients with IVDH is MRI, given its superior anatomic detail,
allowing determination of the affected disc space(s), the lateralization, and dispersion pattern (i.e.
dispersed versus non-dispersed) of the herniated disc material. Comparably, CT has the advantage
of being a faster imaging modality and can diagnose herniation of calcified discs in chondrodys-
trophic dogs. However, if there is no IVDH found on plain CT, CT myelography is necessary to
diagnose compressive lesions. CT with contrast medium may be necessary to identify parenchymal
lesions that contrast enhance, such as nerve sheath tumors or meningiomas. Radiographs can be
used to evaluate for other diseases such as osseous neoplasia and signs that may be associated with
IVDH (e.g. calcified disc material and narrowed disc spaces; Figure 16.1C). Unfortunately, such
findings do not imply compression of the spinal cord making radiographs of limited use.

16.3.1.2 Acute Non-Compressive Nucleus Pulposus Extrusion
In recent years, another type of IVDH has been identified where there is acute extrusion of well-
hydrated disc material that does not cause a compressive myelopathy: acute non-compressive
nucleus pulposus extrusion (ANNPE; De Decker and Fenn 2018). Other terms to describe this
condition include traumatic disc extrusion, high-velocity low-volume disc extrusion, and Hansen
Type III disc extrusion. ANNPE is hypothesized to occur when supraphysiologic forces cause a
small tear in the annulus fibrosus (e.g. during intense exercise or trauma, allowing sudden
extrusion of gelatinous disc material). The force of extrusion into the vertebral canal causes focal