MRI signal void in degenerated canine intervertebral disks may represent calcification or gas

Introduction / Purpose: Gas accumulation in canine intervertebral disk (IVD) degeneration, called vacuum phenomenon (VP), is a common CT finding and it is very different in density from degenerative calcification. In MRI, gas and calcification both cause a signal void. This study aims to establish the prevalence of canine IVD MRI signal void without matching CT IVD calcification.
Methods:
This is a retrospective multicenter study. Imaging archives were searched for matching canine spinal CT and MRI examinations (same segment, acquisition within 24 hours). Sagittal T2 series, presence of mineralization or gas in the IVD in CT were inclusion criteria. In CT, the presence of IVD mineralisation and VP and in MRI the presence and pixel value of MRI IVD signal void were recorded.
Results:
Sixteen cases were included in each VP and calcification group based on the CT findings (gold standard). In MRI, all cases showed an IVD signal void area. One-Way ANOVA showed no statistical difference in pixel value of the signal void areas between both groups (P-value> 0.05).
Discussion / Conclusion:
MRI T2 signal void areas in the canine IVD are not necessarily due to calcification, they can represent VP. IVD calcification, but not VP, is associated with one particular type of IVD degeneration (Hansen-Type-1) with specific clinical signs and prognosis. Therefore, VP and thereby other types of IVD degeneration should be considered when identifying MRI signal void in the canine IVD.