The spinal cord compression is likely responsible for the patient's complaint, not the previous surgical level. The CSF-intensity cyst-like lesion has features of a posterior intradural spinal arachnoid cyst.

The thoracic spine is the most common location of spinal arachnoid cysts with predilection to occur dorsal to the cord. They can be intradural-extramedullary or extradural in location, with the intradural location being less common. They can be primary or secondary to trauma or previous surgery. Secondary arachnoid cysts can be intradural or extradural.

Differential diagnosis is dorsal thoracic arachnoid web, in which there is focal indentation of the spinal cord with scalpel sign.