Breed-specific variations in canine spinal cord anatomy: conus medullaris and dural sac termination and filum terminale internum length.

BACKGROUND: Limited research exists on breed differences in conus medullaris termination (CMT), dural sac termination (DST), and filum terminale internum length (FTIL). Dramatic vertebral column variations exist among breeds, suggesting possible differences in caudal spinal cord structures. This retrospective magnetic resonance imaging (MRI) study aimed to investigate breed-related differences with three cohorts of dogs. Cohort 1 consisted of 117 dogs without spinal cord compression (SCC) to identify demographic influences. Cohort 2 included 37 Corgis with and without SCC to assess if SCC affects the CMT, DST, or FTIL. Cohort 3 comprised 163 dogs to assess the effects of tail morphology and breed. RESULTS: In Cohort 1, heavier dogs had a more cranial CMT and DST (p=<0.001) and longer FTIL (p<0.001, R=0.47). Controlling with L2 mitigated this effect for FTIL (p=0.09, R=-0.16). Age was not associated with CMT or DST, but correlated with FTIL/L2 (p<0.001, R=0.31). Sex had no impact. Most breeds had their CMT at L6. Only Cavalier King Charles Spaniels (CKCS) and Corgis reached the sacrum, while Boston Terriers ended more cranially at L5 or L6. Cohort 2 showed no significant difference in CMT, DST or FTIL/L2 between Corgis with and without SCC (p=0.5, 0.18, and 0.46, respectively). In Cohort 3, weight and tail type affected CMT and DST (p<0.001). Ninety-six percent of normal tailed dogs had a CMT at L6 or L7 while screw tailed breeds ranged from L4-L7 and CKCS terminated at L7 or in the sacrum. These trends were similar for the DST. FTIL/L2 differed between groups with CKCS having a higher ratio and widest range and screw tails the lowest ratio (p<0.001) compared to normal tails. Among breed investigation, CMT differed for CKCS, Corgis, Boston Terriers, English Bulldogs and French Bulldogs versus normal tailed dogs (p<0.001). Similarly, DST varied among breed and by weight (p=<0.001). CKCS and German Shepherds had higher FTIL/L2 ratios, while Boston Terriers, French Bulldogs, and Labradors were lower than other breeds. CONCLUSIONS: This study highlights the importance of considering breed when evaluating the caudal spinal cord anatomy. Variation in the CMT, DST, and FTIL were influenced by weight, tail-type, and breed.