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

OBJECTIVE: To determine whether perioperative management guided by conditional computed tomography-myelography (C-CTM) is non-inferior to magnetic resonance imaging (MRI) regarding functional outcome for acute thoracolumbar intervertebral disc extrusion (IVDE) in non-ambulatory chondrodystrophic dogs. STUDY DESIGN: Quasi-randomized natural experiment utilizing unscheduled MRI downtime as an exogenous instrument. SAMPLE POPULATION: A total of 560 client-owned dogs (MRI, 518 dogs; C-CTM, 42 dogs). METHODS: A retrospective cohort study was conducted. The primary outcome was recovery of ambulation, analyzed with intention-to-treat (ITT) and per-protocol (PP) principles with a prespecified non-inferiority margin of -12%. Secondary outcomes included safety events (postoperative neurologic deterioration, progressive myelomalacia, major complications) and time-adjusted treatment costs. RESULTS: C-CTM was non-inferior to MRI for recovery of ambulation in both ITT (risk difference + 6.5%, 95% CI: -2.7%-15.7%, one-sided p < .001) and PP analyses (risk difference + 2.5%, 95% CI: -7.3%-12.2%, one-sided p < .001). There was no difference in rates of postoperative neurologic deterioration, progressive myelomalacia, or major complications. Total treatment costs and imaging costs were significantly lower for C-CTM (p < .01). There was no difference in non-imaging costs between groups. CONCLUSION: In non-ambulatory chondrodystrophic dogs with acute thoracolumbar IVDE, C-CTM is non-inferior to MRI for recovery of ambulation with a similar safety profile, at significantly lower cost. CLINICAL SIGNIFICANCE: In dogs with a high pretest probability of acute thoracolumbar IVDE, routine use of MRI may not be justified given the comparable clinical outcomes and lower treatment costs achieved with C-CTM.