Tarlov Cyst

Tarlov (perineurial) cysts are outpouchings of the arachnoid and, unlike meningeal cysts, at least part of their wall contains nerve fibers. CSF flows into the space between the endoneurium (extension of the pia mater) and perineurium (extension of the arachnoid mater) under pulsation, and gets trapped via a ball-valve phenomenon. They are most commonly found at the sacral (S2 and S3) nerve roots, where they can be associated with bone erosion, and can rarely cause sciatica.

Differential considerations include meningocele, arachnoid cyst, neurofibroma, and dural ectasia.

References

• IM Tarlov, Spinal perineural and meningeal cysts. J Neurol Neurosurg Psychiatry 33 (1970), pp. 833–843.
• Neuroradiology: The Requisites. Second edition. pp806-807.