The purpose of the study was to determine the effect of dispersed or non-dispersed form of the extruded disk material (EDM) on neurological status and surgical outcomes in thoracolumbar Hansen Type I disk disease (TDD) and to evaluate Magnetic Resonance Imaging (MRI) and clinical findings.

Medical records of 42 dogs with chronic TDD diagnosed by MRI and which have undergone surgical intervention were reviewed. EDM was localized, and classified as Dispersed Disk (DD) or Non-Dispersed disk (NDD) according to dispersion of EDM in epidural space by the MRI. Correlation between MRI findings and intraoperative findings was assessed and evaluation of the effect of dispersion on neurological status at admission and surgical outcomes were carried out.

In eighteen each of 42 cases EDM was lateralized to the left or right side and six of them to the central by MRI. Concomitant disorders such as myelomalacia (n=2), epidural haematoma (n=1) and Hansen Type II disk disease (n=16) were also diagnosed by MRI. Twenty-six of the dogs had DD and the rest had NDD. There was no correlation between the pre­operative neurological status and vertical (VtD) and/or horizontal dispersion (HD) of EDM (P>0.05).

The superiority of MRI in canine TDD for precise diagnosis was demonstrated in detail. The results of this study indicate that the dispersion of EDM should be causing a concussive trauma on spinal cord rather than compression. There was not significant difference between DD and NDD in preoperative neurological status and surgical outcomes (P>0.05).