Computed tomography versus magnetic resonance imaging for the perioperative management of acute thoracolumbar intervertebral disc extrusion in non-ambulatory chondrodystrophic dogs.

C-CTM is non-inferior to MRI for acute thoracolumbar IVDE outcomes with significantly lower treatment costs.

This retrospective cohort study evaluated whether conditional computed tomography-myelography (C-CTM) is non-inferior to MRI for perioperative management of acute thoracolumbar intervertebral disc extrusion (IVDE) in non-ambulatory chondrodystrophic dogs. Using a quasi-randomized natural experiment design leveraging unscheduled MRI downtime as an exogenous instrument, 560 client-owned dogs were included (518 MRI, 42 C-CTM). The primary outcome was recovery of ambulation, analyzed using both intention-to-treat (ITT) and per-protocol (PP) principles with a prespecified non-inferiority margin of -12%. C-CTM demonstrated non-inferiority to MRI in both ITT (risk difference +6.5%, 95% CI: -2.7% to 15.7%) and PP analyses (risk difference +2.5%, 95% CI: -7.3% to 12.2%). Secondary safety outcomes—including postoperative neurologic deterioration, progressive myelomalacia, and major complications—showed no significant differences between groups. Notably, total treatment costs and imaging costs were significantly lower in the C-CTM group (p < .01), while non-imaging costs did not differ. The study concludes that in dogs with high pretest probability of acute thoracolumbar IVDE, routine use of MRI may not be clinically justified when C-CTM yields comparable functional outcomes and safety profiles at reduced cost. Limitations include the retrospective design, substantial group size disparity, and potential selection bias, though the natural experiment methodology partially mitigates confounding. These findings have meaningful implications for resource allocation and accessibility of care in clinical practice.

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