Hernias of intervertebral discs are a common canine disease that is usually treated surgically. Recently, a histological scoring system for surgically removed canine intervertebral herniated discs has been developed by scoring the lesions of both the anulus fibrosus (AF) and the nucleus pulposus (NP). Since the proportion of AF and NP in the surgical samples may vary, depending on the surgical approach, the aim of this study is to grade separately the lesions in AF and NP and to modify the previously described scoring system adding three parameters: inflammation, mineralization and neovascularization. Possible association of the modified grading system with clinical parameters were statistically assessed. Herniated disc material was collected from 27 dogs. AF was present in 10/27 cases and was classified as grade 2 in 4 cases, grade 3 in 5 cases and grade 4 in 1 case. The NP was present in all 27 cases and was classified as grade 2 in 1 case, grade 3 in 5 cases, grade 4 in 9 cases and grade 5 in 12 cases. A statistically significant association was evidenced between short pre-operative period and higher grade of both the NP and of the AF (P<0.01). Separating the grades of the AF and NP can be useful for a fair assessment of degeneration, and circumventing the limitation of the qualitative and quantitative variability of samples.

Key words: Clinical and neurological signs, Disc herniation, Dog, Histology, Scoring system