Computed tomographic myelography of the cranial cervical vertebral column in unaffected Warmblood horses - comparison of transverse vertebral ratios in the flexed and neutral cranial cervical vertebral column.
Authors: Hellige Maren, Schröder Caroline, Seehusen Frauke, Rohn Karl, Geburek Florian
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Computed tomographic myelography (CTM) remains the gold standard for diagnosing extradural spinal cord compression in horses, yet baseline reference data for how normal cervical anatomy changes with neck position has been limited, particularly in large breeds. Maren Hellige's team acquired high-resolution transverse CTM images at the C3–C4 region in 13 neurologically sound Warmblood horses in both neutral and flexed positions, then calculated three key area ratios: the cord canal area ratio (CCAR), dural canal area ratio (DCAR), and cord dural area ratio (CDAR). The flexed cervical position produced significant biomechanical changes: the DCAR—representing the space available for the dura mater within the vertebral canal—decreased significantly at multiple sites (intravertebral cranial and caudal regions of C3 and C4, plus intervertebral spaces inter1 and inter2), whilst the CDAR increased significantly at all three intervertebral locations, indicating the spinal cord occupied proportionally more space within the dural tube during flexion. The CCAR itself remained stable, suggesting the cord's absolute cross-sectional area did not change but the available extradural space was reduced. These findings establish critical reference parameters for clinicians interpreting CTM scans in symptomatic horses with suspected cervical myelopathy; distinguishing between pathological compression and the physiological reduction in extradural clearance that occurs with neck flexion is essential for accurate diagnosis and determining whether clinical signs warrant intervention or represent positional phenomena in otherwise structurally normal animals.
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Practical Takeaways
- •CTM imaging of the cervical spine should account for positioning (flexion vs. neutral) as this significantly affects vertebral ratios used to diagnose spinal cord compression
- •Normal reference ranges established here can help differentiate pathological compression from normal anatomical changes during cervical flexion in diagnostic imaging
- •When evaluating horses with suspected cervical myelopathy, standardizing positioning during CTM is critical for accurate interpretation of spinal cord and canal measurements
Key Findings
- •Dural canal area ratio (DCAR) decreased significantly (p < 0.05) during cervical flexion compared to neutral position in unaffected horses
- •Cord dural area ratio (CDAR) increased significantly (p < 0.05) at all intervertebral sites (inter1-3) during flexion
- •DCAR reductions occurred intravertebral at cranial and caudal sites of C3-C4 and at intervertebral sites inter1 and inter2
- •Establishment of normal vertebral ratio reference values for flexed and neutral cervical positions in healthy Warmblood horses