The value of oblique versus ventrodorsal myelographic views for lesion lateralisation in canine thoracolumbar disc disease

OBJECTIVE: To determine the value of oblique versus ventrodorsal myelographic views for lesion lateralisation in canine thoracolumbar disc disease. METHODS: The ventrodorsal and oblique views from 196 lumbar myelograms of dogs with single thoracolumbar disc extrusions or protrusions were blindly and independently reviewed by two of the authors for evidence of lesion lateralisation. Medical records were reviewed for details regarding hemilaminectomy surgery. The side (left versus right) of the surgery and whether or not the disc material was retrieved were noted. RESULTS: Both reviewers lateralised significantly more disc lesions from the oblique views (93 and 95 per cent) than from the ventrodorsal views (59 and 70 per cent) (P<0.001). Using a combination of oblique and ventrodorsal views, 194 (99 per cent) and 195 (99.5 per cent) lesions were lateralised. Unilateral hemilaminectomy was performed in 193 dogs with myelographic lateralisation and in one dog without myelographic lateralisation. The side of spinal cord decompression corresponded with the myelographic findings in all dogs showing lateralisation on myelography. In the dog without myelographic lateralisation, a left (randomly chosen) hemilaminectomy revealed dorsal protrusion of the annulus fibrosus. CLINICAL SIGNIFICANCE: Myelography, including oblique, ventrodorsal and lateral views, is an accurate method for determining lateralisation of extruded or protruded disc material in the vertebral canal before decompressive surgery. Combined oblique and ventrodorsal views are more useful than either view alone and should be routinely obtained in all lumbar myelographic studies when investigating thoracolumbar disc disease.