Tarlov cysts are cerebral-spinal fluid filled  'perineurial' cysts along the sacral and lower lumbar nerve roots.

Susan Presberg-Greene, MD’s story of her IC diagnosis reads just like so many others. In 1998, she suddenly had terrible burning urethral pain. She’d had urinary tract infections before, so she thought this was another one and took antibiotics...

Treatment of Symptomatic Perineural (Tarlov) Cysts  

Donlin M. Long M.D., PhD. 
Johns Hopkins Medicine, Baltimore, Maryland