Agreement of surgeon's perception of the effectiveness of spinal cord decompression with findings on postoperative magnetic resonance imaging for dogs surgically treated for intervertebral disk extrusion

Abstract

OBJECTIVE To determine the accuracy of the surgeon's perception versus postoperative MRI findings in assessing the effectiveness of spinal cord decompression achieved in dogs surgically treated for intervertebral disk extrusion (IVDE) and whether postoperative MRI findings were more likely to be associated with various outcomes. ANIMALS 68 dogs surgically treated for cervical or thoracolumbar IVDE. PROCEDURES Data on clinical, neurologic, pre- and postoperative MRI, and intraoperative findings as well as outcomes and recovery times (6-month follow-up period) were prospectively collected and compared between various groups. RESULTS 54 (79%) dogs had thoracolumbar IVDE, and 14 (21%) had cervical IVDE. Median degree of spinal cord compression as assessed on transverse T2-weighted MRI images was 45.6% before surgery and 8.8% after surgery. The correlation between surgeons' perception (n = 3) and postoperative MRI findings for the degree of spinal cord decompression achieved was only fair (κ = 0.40). Unsatisfactory spinal cord decompression as assessed via postoperative MRI was associated with severity of preoperative neurologic grade and preoperative compression, thoracolumbar (vs cervical) IVDE, and ventral (vs ventrolateral or dorsolateral) circumferential distribution of extruded material. Satisfactory (vs unsatisfactory) decompression as assessed via MRI was associated with a lower postoperative neurologic grade, greater likelihood of a successful outcome, and lower mean recovery time. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that for dogs surgically treated for IVDE, the surgeon's perception of adequate spinal cord decompression may be less reliable than postoperative MRI findings. Postoperative MRI appeared particularly useful for dogs with a severe preoperative neurologic status, severe preoperative spinal cord compression, and thoracolumbar IVDE.

Diagnostic Imaging in Intervertebral Disc Disease

“…A common categorization is based on the percentage of reduction in spinal cord diameter, graded as mild (<25%), moderate (25 to 50%), or severe (>50%) (102,103). Morphometric estimates of crosssectional area of either spinal cord or extruded material offer even more precise information (104)(105)(106). The degree of spinal cord compression seen on transverse MR images in cases of IVDE was associated with the severity of pre-operative neurological signs in the cervical spine (107), but not in the thoracolumbar region (94,108,109).…”

“…Interestingly, a recent low-field MRI study of IVDE found spinal cord hyperintensity on T2W images in 18% of dogs in the preoperative period. MRI was repeated after decompressive surgery (immediately after surgery in most dogs) and the number of dogs with hyperintensity almost doubled (34%) (105). The relationship between spinal cord hyperintensity and prognosis of IVDD can be found in the article "Prognostic factors in acute spinal cord injury" in this issue.…”

“…In all cases where planning differed, a significantly larger hemilaminectomy defect (a greater number of articular facets removed) was planned using MRI compared to CT (70). MRI is also a very useful modality to investigate patients in the post-operative period (105,(120)(121)(122). MR imaging can differentiate residual extruded nucleus from hemorrhage, based on signal intensity and gradient echo characteristics (101,120).…”

“…A recent prospective low-field MR study evaluated the agreement between surgeon's perception of spinal cord decompression and residual disc on postoperative MR images acquired immediately after surgery in most cases (105). In most instances in which the MRI results differed from the surgeon's perception, the degree of surgical decompression was perceived as satisfactory by the surgeon, but was revealed as unsatisfactory via MRI.…”

“…In most instances in which the MRI results differed from the surgeon's perception, the degree of surgical decompression was perceived as satisfactory by the surgeon, but was revealed as unsatisfactory via MRI. This was observed primarily in large disc extrusions (105). The clinical outcome of those dogs with unsatisfactory spinal cord decompression was worse than those with adequate spinal cord decompression (105).…”