A 58 year-old woman presented with pain in the low back radiating down the right leg.

Tarlov or perineurial cysts are located in the potential space between the peri- and endoneurium of the posterior spinal nerve root sheath. They occur commonly in the adult population, and are most often found in the sacral region. Although often asymptomatic, when they are present in the sacral neural canal and foramina, they can result in a variety of symptoms, including radicular pain, paresthesias, and urinary or bowel dysfunction. The distinctive feature of the Tarlov cyst is the presence of spinal nerve root fibers within the cyst wall or the cyst cavity itself, although the term Tarlov cyst has often been erroneously applied to other cystic spinal lesions.