Sonia González-Medina, Myra F. Barrett, Tawfik A. Aboellail, Bradley B. Nelson, Yvette S. Nout-Lomas
Background
Cervical vertebral compressive myelopathy (CVCM, “wobbler syndrome”) is a major cause of ataxia in horses. Diagnosis typically relies on radiographic myelography, but this method can underestimate compression and is prone to variability. CT myelography offers better anatomical detail, but objective diagnostic thresholds are lacking. This study aimed to establish morphometric parameters using cone beam CT (CBCT) myelography, compare them with radiographic findings, and correlate results with histopathology.
Methods
A prospective observational study was performed in 14 horses: 10 with CVCM confirmed by postmortem examination and 4 neurologically normal controls. Horses underwent radiographs, radiographic myelography (neutral, flexed, extended), and CBCT myelography in dorsal recumbency. Morphometric measurements (vertebral canal dimensions, spinal cord area, dural area, myelographic area) were collected. Receiver operating characteristic (ROC) analysis established diagnostic thresholds. Postmortem histology validated spinal cord compression.
Results
-Intravertebral sagittal ratios were significantly lower in CVCM horses (<50% at ≥1 site) compared to controls (>52%).
-Radiographic myelography identified 18 compressed sites; CBCT identified 13 compressed sites; postmortem confirmed 21.
-CBCT underestimated some compressions, particularly at C3–C4, but provided quantitative measures of spinal cord and dural space.
Key diagnostic thresholds:
-Full myelographic area <294 mm²
-Dural area <188 mm²
-Spinal cord area <104 mm²
-Compression thresholds included full myelographic area <274 mm², dural area <188 mm², dural area reduction >14%, and spinal cord area/dural area ratio >57.9%.
-Histopathology confirmed Wallerian degeneration and white matter damage at compressed sites.
Limitations
The study included a small number of horses, and the CVCM horses were younger than controls, which could affect comparisons. CBCT was performed only in neutral neck positions, potentially missing dynamic compressions.
Conclusions
CBCT myelography provides objective, quantitative parameters to support the diagnosis of CVCM and complements radiographic myelography. While CBCT may underestimate certain compressions, especially in flexion-dependent lesions, it improves characterization of spinal cord and dural dimensions. Future advances in dynamic CT and age-matched larger cohorts will further refine diagnostic criteria.
Dimensions obtained from diagnostic imaging. Location of measurements from lateral cervical radiographs (A), radiographic myelograms (B), and CT images (C). In the lateral radiograph the location of C3 is shown (A). In the radiographic myelogram the location of C3 and C3–C4 is shown (B). In the transverse CT image the location of the C4–C5 intervertebral space is shown (C) and the location of the full myelographic area (dural area plus spinal cord area) is identified within the red line and the spinal cord area is identified within the purple line. The blue and green lines are generated by the CT software in multiplanar display. SR-A, intravertebral minimum sagittal diameter; SR-B: maximal height of the cranial vertebral physis; Sagittal ratios are calculated based on SR-A/SR-B. DMC, dorsal myelographic column (black line); DD, dural diameter (double arrowheads); SCH, spinal cord height (white line).
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