SummaryTarlov cysts are fluid-filled sacs that affect the nerve roots of the spine, especially near the base of the spine (sacral region). Individuals may be affected by multiple cysts of varying size. In most cases, Tarlov cysts do not cause symptoms (asymptomatic). However, symptoms can occur depending upon the size and specific location of the cyst. Generally, the larger a Tarlov cyst is, the more likely it is to cause symptoms. Symptoms sometimes caused by Tarlov cysts include pain in the area served by the affected nerves, numbness and altered sensation, an inability to control bladder and bowel movements (incontinence), impotence, and, rarely, weakness in the legs. Small, asymptomatic cysts can slowly increase in size eventually causing symptoms. The exact cause of Tarlov cysts is unknown, but they may occur due to variation in normal development of the nerve sheath. Tarlov cysts were first described in the medical literature in 1938.