Case 6: 5-year-old male neutered Pointer

• Cervical and thoracolumbar spinal cord and nerves are normal size and signal intensity in the T2 and STIR images
• No arachnoid abnormalities are identified in the myelogram.
• A rounded low signal intensity focus that is seen in the cranial aspect of the right C7-T1 foramen and therefore in the path of the right C8 nerve
• Right C8 nerve is compressed against the dorsal articular bone based on comparison to the contralateral nerve. Enlargement of the nerve around this focus is not seen
• Multifocal cervical or thoracolumbar disc desiccation without clinically significant herniation
• Included paraspinal anatomy and thoracic and abdominal cavities are normal

1) Right C8 nerve compression due to foraminal focus of presumed extruded disc material.

2) No macroscopic thoracolumbar abnormalities to explain pain.

3) Diffuse degenerative intervertebral disc disease of the cervical and thoracolumbar spines.

With foraminal or lateralized disc herniations, pain and often severe pain are the primary and most consistent presenting clinical sign. Depending on the location of of the extruded disc material, there may be lameness or a nerve root signature. The diagnosis of a foraminal or lateral disc extrusions requires a robust imaging protocol.

There is minimal literature in human or veterinary literature on protocols for identification of these disc extrusions. In the cervical area, a protocol of T2 and T1 sagittal and transverse images, as well as a T2 GRE sequence performed well in a small number of cases (n=13 dogs). Different imaging strategies when concerned for a foraminal or lateralized disc could be considered to take advantage of image resolution principles.

1) Application of Fluid Sensitive Sequence T2 and STIR images are ideal for screening areas, including the vertebral column outside the vertebral canal. Since both are fluid sensitive, but STIR has increased conspicuity of pathologically altered spinal nerves. The abnormal nerves are hyperintense or enlarged and more visible with the suppression of surrounding fat. However, if both are run in the sagittal plane, than one is not gaining complete anatomic or chemical information in the areas of the spinal nerve. STIR dorsal or fat-suppressed T2 dorsal images will provide the highest resolution of the of the foraminal spinal nerve and lateral contour of the disc. The other advantage is radiculoneuritis is more easily detected in the dorsal plane since the left and right foraminal areas can be compared.

2) T2 or PD transverse images through EVERY disc This is not a bad strategy in the cervical spine, where 3-5 slices through each disc/foramen can be acquired in 4-6 minutes depending on your MRI. It will be time consuming in the thoracolumbar spine, especially if pain is not localized.

3) 3-D isotropic or near-isotropic sequences These are newer sequences and not available on older units unless software is purchased. These are single sequences acquired in 8-9 minutes. Submillimeter resolution sagittal images are acquired and can be reconstructed in any desired plane. Therefore, dorsal, oblique and transverse plane images can be produced including transverse images through every disc/foramen.

References

Carpentier-Anderson et al. (2016) 3D Magnetic Resonance Imaging of the Dog Spine in Hansen Type I Intervertebral Disk Disease. 2016 ACVIM Forum Research Abstracts

Fadda et al. (2013) Far lateral lumbar disc extrusion: MRI findings and surgical treatment. Vet Comp Orthop Traumatol. Chambers et al. (1997) Diagnosis of lateralized lumbosacral disk herniation with magnetic resonance imaging. Journal of the American Animal Hospital Association: July 1997, Vol. 33, No. 4, pp. 296-299.