MRI Signal Void in Canine Disks: Mineralization or Gas? New CT-Validated Evidence

MRI Signal Void in Degenerated Canine Intervertebral Disks May Represent Mineralization or Gas

Yasamin Vali; Carola Daniel; Eberhard Ludewig; Tobias Schwarz

Background

Magnetic resonance imaging (MRI) is widely used for diagnosing canine intervertebral disk disease (IVDD). Intradiskal hypointense or signal void areas on T2-weighted MRI are commonly attributed to mineralization; however, gas accumulation within degenerated intervertebral disks (vacuum phenomenon, VP) may produce similar MRI findings. Computed tomography (CT) reliably differentiates mineralization from gas based on attenuation values, but MRI cannot inherently distinguish between them. The study aimed to determine whether MRI signal voids correspond to gas or mineralization and whether MRI features allow differentiation between the two entities.

Methods

This retrospective multicenter study included dogs that underwent both spinal CT and MRI of the same vertebral segment within 48 hours. Inclusion required CT-confirmed intradiskal gas (≤ −900 HU) or mineralization (≥ 900 HU) and corresponding sagittal T2-weighted MRI images. Disks containing both gas and mineralization were excluded. CT findings were classified by location (nucleus pulposus or annulus fibrosus and zonal distribution) and shape (spot, linear, island, mixed). MRI T2-weighted images were assessed for corresponding signal voids, with pixel intensity measurements recorded. Statistical analyses included Fisher’s exact test and Mann–Whitney U test.

Results

Twenty-six studies contributed 32 intervertebral disk spaces (16 gas, 16 mineralization). All disks with gas on CT demonstrated corresponding hypointense or signal void regions on MRI. Mean MRI pixel intensity values did not significantly differ between mineralization and gas groups (p = 0.5). Mineralization maintained consistent location between CT and MRI, whereas gas demonstrated significant location changes between modalities (p = 0.03). No statistically significant differences were identified in shape distribution between groups, although mixed patterns were observed only in the gas group. Both entities most commonly involved the nucleus pulposus.

Limitations

The study sample size was limited, and variability in dog size, imaging parameters, and scanner settings may have influenced findings. Single-point pixel measurements rather than region-of-interest averages were used. Disks containing both gas and mineralization were excluded, further reducing sample size. Differences in physical principles between CT and MRI may also affect comparability.

Conclusions

MRI T2-weighted signal voids within canine intervertebral disks may represent either mineralization or gas. Pixel intensity, location within the disk, and shape do not reliably differentiate between these entities. Therefore, vacuum phenomenon should be included as a differential diagnosis when intradiskal signal voids are identified on MRI. Awareness of this distinction may improve interpretation of canine spinal imaging and refine diagnostic and prognostic assessment in IVDD.

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