A syrinx is an intradural, intramedullary, well-defined collection of fluid that follows CSF signal intensity on all MRI sequences. In some patients, the signal is brighter than CSF on T1WI and darker that CSF on T2WI, possibly due to higher protein content secondary to cord edema.
The etiology of a syrinx can be developmental such as in the Chiari/Dandy Walker malformations or secondary to trauma, tumors, inflammation and ischemia. In cases of an unexplained syrinx, one should suspect a tumor and imaging with gadolinium may be obtained to search for a source.
The above images are from a patient who suffered a retropulsed T6 fracture. Caudal expansion of the central canal with a CSF containing structure is most consistent with a post-traumatic syrinx.
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