Can hydromyelia differentiate acute versus chronic IVDE?

Association of hydromyelia and acute compressive myelopathy caused by intervertebral disc extrusion in dogs

Philippa J. Johnson, Amy B. Todd-Donato, Andrew D. Miller, Yu Wang, Chris Holm, Carolina I. Panisello-Manterola, Claudia S. Colón Acevedo, Jonathan H. Wood

Background
Intervertebral disc extrusion (IVDE) leading to compressive myelopathy is a prevalent cause of spinal cord injury in dogs. Hydromyelia, a distension of the central canal of the spinal cord, is often observed in association with IVDE. This study investigated the MRI features of hydromyelia and its relationship to clinical history, neurological severity, and duration of spinal cord compression.

Methods
A retrospective observational study analyzed 91 client-owned dogs with thoracolumbar IVDE. Inclusion criteria required a single site of IVDE and high-quality MRI imaging. Hydromyelia was graded (absent, mild, or severe) and localized (cranial, caudal, or both). Clinical history and neurological severity were reviewed, and statistical analyses were performed to explore correlations between hydromyelia and clinical features.

Results
-Hydromyelia Presence: Observed in 84 of 91 dogs, primarily cranial to the compression site (76%), and both cranial and caudal in 21%.

-Duration of Clinical Signs:
-Cases with absent hydromyelia had significantly longer clinical signs (mean: 73.1 days) compared to mild (mean: 17.7 days) and severe hydromyelia
(mean: 17.9 days; p = 0.006).
-A clinical duration under 14 days was 78.6% sensitive and 85.7% specific for predicting hydromyelia presence.

-Neurological Severity and Compression:
-No significant differences in neurological severity grades (e.g., spinal pain, paraparesis, paraplegia) were found across hydromyelia grades.
-Compression ratios showed no significant variation between groups.

Limitations
The study was retrospective, with some variability in MRI sequences and slice thickness, potentially reducing hydromyelia detection. Additionally, only a small subset of cases lacked hydromyelia, limiting statistical power.

Conclusions
Hydromyelia is a common MRI feature in dogs with acute IVDE (<14 days) and is less likely to occur in chronic IVDE. Its absence might help identify chronic lesions, aiding surgical planning. However, its utility as a diagnostic marker should be considered alongside clinical and neurological assessments.

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