Case 5

This is an MRI dorsal spine study showing a focal dorsal indentation on the posterior surface of the spinal cord at T4 level, a finding which is termed the ‘scalpel sign’. At this level, there is subtle anterior displacement of the cord with widening of the posterior CSF arachnoid space. 

I note that there is no altered signal of the cord at this level. Incidentally, there is some anterior osteophytosis.

The findings are characteristic of an arachnoid web. The differential diagnosis includes an arachnoid cyst.

I would raise this case for discussion at spinal surgery MDT.