Perineurial cysts, also known as Tarlov cysts, were first described in 1938 by the neurosurgeon Isadore M. Tarlov during an autopsy of the lower spine . He described them as nerve-root membranes that contain fluid collections with restricted communication with the CSF in the thecal sac. These cysts form only on dorsal roots because only the cell bodies of sensory neurons migrate out from the spinal cord during embryonic development, leaving behind a sleeve of dura and subarachnoid space [1, 5-6].