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.

Overview

• This study investigates how flexing the neck affects certain anatomical ratios around the spinal cord in healthy Warmblood horses, using computed tomographic myelography (CTM), a specialized imaging technique.
• The research compares cross-sectional area ratios at specific cervical vertebrae sites in neutral (normal) and flexed neck positions to better understand spinal cord and surrounding structures under different postural conditions.

Introduction

• Computed tomographic myelography (CTM) is a diagnostic imaging technique used to identify extradural spinal cord compression.
• Despite its utility, baseline data on transverse vertebral ratios (proportions between spinal cord, vertebral canal, and dural tube sizes) in healthy horses, particularly under different neck positions, is lacking.
• Understanding these ratios in both neutral and flexed positions provides essential reference values necessary to interpret CTM in clinical cases and diagnose spinal issues more effectively.

Objective of the Study

• To compare cross-sectional area ratios of spinal cord, vertebral canal, and contrast-enhanced dural tube in the cervical vertebral column of neurologically normal Warmblood horses.
• Specifically focused on the C3-C4 vertebrae region in two positions: neutral (standard) and flexed cervical column positions.

Methods

• Sample: 13 neurologically unaffected Warmblood horses.
• Imaging: CTM scans performed in two positions of the neck: neutral and flexed.
• Sites of measurement:
  • Intervertebral sites (between vertebrae, labeled inter1 to inter3).
  • Intravertebral sites (within vertebrae, further divided into cranial, middle, and caudal regions).
• Ratios calculated:
  • Cord Canal Area Ratio (CCAR): cross-sectional area (CSA) of spinal cord divided by CSA of vertebral canal.
  • Dural Canal Area Ratios (DCAR): CSA of contrast-enhanced dural tube divided by CSA of vertebral canal.
  • Cord Dural Area Ratios (CDAR): CSA of spinal cord divided by CSA of contrast-enhanced dural tube.
• Statistical comparison of ratio differences between neutral and flexed neck positions.

Results

• DCAR (Dural Canal to Vertebral Canal Ratio):
  • Significantly decreased in the flexed neck position compared to neutral (p < 0.05).
  • Decrease localized intravertebrally at cranial and caudal parts of C3 and C4 vertebrae.
  • Significant decreases also found at intervertebral spaces labeled inter1 and inter2.
• CDAR (Spinal Cord to Dural Tube Ratio):
  • Significantly increased in the flexed neck position compared to neutral across all intervertebral sites (inter1 to inter3).
  • This suggests the spinal cord occupies a larger proportion of the dural tube’s cross-sectional area during flexion.
• CCAR (Spinal Cord to Vertebral Canal Ratio):
  • No significant changes reported between flexed and neutral positions.

Interpretation of Findings

• Flexion of the cervical spine compresses or reduces the size of the dural sac within the vertebral canal, resulting in a smaller dural canal area ratio.
• Because the dural tube area decreases, the relative size of the spinal cord compared to the dural tube increases (CDAR increases), indicative of the dural sac’s deformation during flexion.
• The vertebral canal’s size remains relatively stable, as CCAR ratios were not significantly affected by flexion.
• These biomechanical changes are observed in specific cervical spine regions (C3-C4), which can be critical zones in equine cervical spinal health.

Clinical Implications

• Baseline reference values for transverse vertebral ratios in neutral and flexed positions provide veterinarians with essential comparative data when interpreting CTM in horses.
• Understanding positional effects on the dural tube and spinal cord morphology helps differentiate normal flexion-related changes from pathological compressions or lesions.
• Imaging protocols may consider including flexed views for comprehensive assessment of cervical spinal cord space and potential compressions.
• This research supports more accurate and position-aware diagnosis of cervical spinal cord diseases in Warmblood horses and potentially other breeds.

Summary

• This study demonstrates that neck flexion in healthy Warmblood horses causes measurable changes in the dural tube’s cross-sectional area relative to the vertebral canal and spinal cord.
• These changes, identified using CT myelography, provide crucial normative data to better assess cervical spinal health and disease through imaging.