Neurological deterioration following decompressive spinal surgery for disc herniation such as hemilaminectomy is fortunately not too common. When it occurs, prompt reassessment often using repeat imaging, is key. Common causes in the early post-operative period include residual herniated disc material, re-herniation or hematoma formation. 
 

Below are the MR images of a French bulldog. This dog underwent right-sided L4/5 hemilaminectomy for disc extrusion causing ambulatory paraparesis and lumbar pain. The day after surgery, the dog deteriorated neurologically to become non-ambulatory and severely paraparetic. Repeat MR images show marked T2W and STIR bilaterally symmetrical hyperintensity affecting the grey matter from L3/4 to mid-L5. These changes were isointense on T1W. No residual herniated disc material was present confirming adequate decompression of the cord.

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These changes were considered suggestive of poliomyelomalacia which is suspected to be caused by spinal cord ischaemia. The cause of this pathological process is still hypothetical and ranges from venous outflow obstruction as seen in horses with a similar condition, adverse anaesthetic events (systemic hypotension or deceased cardiac output), increased intraparenchymal or subarachnoid pressure, which may be present with spinal cord compression, or more likely a combination of factors. The prognosis for recovery is unfortunately guarded and there is no specific treatment besides supportive care.

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