Cone beam computed tomographic myelography in horses with cervical vertebral compressive myelopathy.

Background: While computed tomographic (CT) myelography is increasingly available and has been evaluated in alive horses, objective criteria for diagnosing cervical vertebral compressive myelopathy (CVCM) are lacking.

Objectives: To establish morphometric dimensions of the cervical vertebral canal and spinal cords from horses with CVCM and compare those to unaffected horses with the use of cone beam CT (CBCT).

Study design: Prospective observational study.

Methods: Four control horses and ten horses with CVCM underwent diagnostic imaging and histopathology. Morphometric measurements were obtained from cervical radiographs and radiographic and CBCT myelography. Receiver operating characteristic curves were generated to establish thresholds of measurements.

Results: Intravertebral sagittal ratios were significantly different between CVCM and control horses. Dorsal myelographic column reduction was significantly different between compressed sites and non-compressed sites. Full myelographic area, dural area, and spinal cord area were significantly smaller in the CVCM horses, and were significantly smaller at compressed sites when compared to non-compressed sites. Reductions of full myelographic area and dural area and ratios of spinal cord area to full myelographic area and dural area were significantly larger at compressed sites when compared to non-compressed sites. Diagnostic thresholds to consider for CVCM are full myelographic area <294 mm², dural area <188 mm², and spinal cord area <104 mm². Compressed sites were associated with thresholds of full myelographic area <274 mm², dural area <188 mm², or reduction of full myelographic area >9%, reduction of dural area >14%, spinal cord area: full myelographic area >36.7%, and spinal cord area: dural area >57.9%.

Main limitations: Small number of horses. CVCM horses were younger than control horses.

Conclusions: CBCT myelography provides quantitative parameters that can support a diagnosis of CVCM and should be used alongside radiographic myelography.