3D CT volumetric analysis of spinal canal volume in Bichon Frisé, Dachshund, and French Bulldog: correlation with neurologic severity in thoracolumbar disc herniation

French Bulldogs showed a significantly larger mean spinal canal volume than those of Dachshunds and Bichons (<i>p</i> < 0.05 for both comparisons). Across all dogs, smaller canal volumes were associated with more severe neurological deficits (Spearman <i>ρ</i> ≈ -0.72, <i>p</i> = 0.0014). Across all breeds, disc herniations were most frequently observed at the thoracolumbar junction (T12-L2; 5 of 21 cases), but substantial overlap existed with neighboring segments. The thoracolumbar junction is especially susceptible to disc herniation because it is a transition zone between the rigid thoracic spine and the mobile lumbar spine, where mechanical stress is concentrated and spinal canal reserve space is limited. The 3D volumetric analysis of the vertebral canal is a feasible adjunct to routine imaging and reveals significant breed specific differences. Narrower canal volume appears to exacerbate the impact of disc herniation on the spinal cord, suggesting that canal size is a contributing risk factor for neurologic severity. A critical volume threshold (~1,700 mm³ per vertebral segment) was observed, under which dogs were markedly more likely to develop severe deficits.