MRI is an excellent tool for assessing vertebral column disorders in domestic species.
Magnetic resonance imaging (MRI) has revolutionized the assessment of vertebral column disorders in both humans and animals. It is noninvasive, provides the clinician with data in multiple image planes, and offers outstanding soft tissue contrast. Certain imaging features may be associated with pathologic processes and can be of prognostic value. Furthermore, MRI may be the only reliable antemortem means of diagnosing certain diseases, such as ischemic myelopathy.
In human medicine, MRI has largely replaced both myelography and computed tomography (CT) as the imaging study of choice for patients with vertebral column disease, and this transition has already begun in veterinary medicine.
The selection of an appropriate imaging modality should be based on its sensitivity and specificity for detecting disease and associated adverse events as well as for identifying prognostic data. MRI offers equivalent and often superior sensitivity and specificity when compared with other imaging modalities used in human vertebral column diseases. Evidence-based comparisons between modalities are more limited in veterinary medicine, but currently available data do parallel what is known in human medicine.1-7
Use in Clinical Disease Conditions
In humans, the accuracy of MRI for detecting disk herniation has been shown to be equivalent to or better than either CT or myelography.1 Of importance, much of these data were generated in the 1980s, when the capabilities of MRI were limited by field strength and software.
Comparative data between MRI and other modalities for cervical and thoracolumbar disk herniation in dogs does not exist. In some instances, neither myelography nor CT has identified disk herniation as clearly as MRI has (Figure 1).
Figure 1. Transverse CT and MRI in a dog with paraplegia. CT shows a subtle hyper- to iso-attenuating, right-sided ventral extradural compressive lesion (A and B) at the level of L2-L3 (arrowhead in A). Transverse T2-weighted MRI shows a large, hypointense, ventral and right lateral extradural compressive lesion (C and D) that nearly entirely effaces the cross-sectional area of the vertebral canal (small arrow in D). The visible spinal cord is reduced to a small crescent (large arrowhead in C) and is hyperintense, which may indicate the presence of intraparenchymal edema or necrosis. Surgical exploration confirmed the presence of severe spinal cord compression due to disk extrusion.