MRI thoracic spine
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Focal ventral displacement of the upper thoracic cord to abut the anterior dura, without clear herniation of cord through a dural defect. The posterior CSF space is focally enlarged, with preservation of normal CSF flow artefact. Increased cord T2 signal in identified just above the focal cord of compression.
The shape of the cord distortion resembles a scalpel blade, the 'scalpel sign' that suggests dorsal arachnoid web. An often associated findings that is not present in this case is syringomyelia, thought to be due to alterations in CSF flow.
The imaging differential diagnosis would be ventral cord herniation or adhesion. When the cord is closely apposed to the anterior dura these conditions can be difficult to differentiate.