Perineural cysts, which are also known as Tarlov cysts, are fluid-filled sacs that form on nerves at the base of the spine. They form around the roots of nerves in this part of the body. Perineural cysts are different from other cysts that can form in the sacrum because the nerve fibers from the spine are found within the cysts. Women are more likely than men to develop them.
A person with such cysts would likely never know it. They almost never cause symptoms. When they do cause symptoms, however, the most common one is pain in the lower back, buttocks, or legs. This occurs in rare cases when the cysts become enlarged with spinal fluid and press on nerves.
Because they rarely cause symptoms, perineural cysts are often not diagnosed. A doctor can determine if you have the cysts using imaging techniques. Perineural cysts are often misdiagnosed because symptoms are so rare. The cysts can be drained to provide temporary relief of symptoms. Only surgery can keep them from coming back or refilling with fluid and producing symptoms again. In rare cases, cysts that cause symptoms and are not treated will cause permanent damage to the nervous system.
People with perineural cysts are not likely to have any symptoms. Most people who have them never know they are there. Symptoms only occur when the cysts fill up with spinal fluid and expand in size. When this happens, the enlarged cysts can compress nerves and cause other problems.
The most common symptom associated with perineural cysts is pain. The enlarged cysts can compress the sciatic nerve, causing sciatica. This condition is characterized by pain in the lower back and buttocks, and sometimes down the back of the legs. The pain can be sharp and sudden or more mild and achy. Sciatica is also often accompanied by numbness in the same areas, and muscle weakness in the feet and legs.
In severe cases where perineural cysts have enlarged, there can be a loss of bladder control, constipation, or even sexual dysfunction. Having these symptoms is possible, but very rare.
The root cause of cysts in the base of the spin is unknown. But there are reasons why these cysts can grow and cause symptoms. If a person experiences some type of trauma in the back, perineural cysts can begin to fill up with fluid and cause symptoms. Types of trauma that can trigger symptoms include:
- heavy exertion
Because most perineural cysts cause no symptoms, they are typically never diagnosed. Your doctor can order imaging tests to identify them if you have symptoms. MRIs can show cysts. A CT scan with a dye injected into the spine can show if fluid is moving from the spine into cysts in the sacrum.
For most cases of perineural cysts, no treatment is needed. But if you have symptoms, they may need treatment to relieve pressure and discomfort. A quick fix is to drain the cysts of fluid. This can relieve symptoms immediately, but it is not a long-term treatment. The cysts usually fill up again.
The only permanent treatment for perineural cysts is to have them surgically removed. Surgery is usually recommended for serious, chronic pain, as well as bladder problems from the cysts.
In the large majority of cases of perineural cysts, the outlook is excellent. Most people with these cysts will never have any symptoms or need any treatment. Only 1 percent of people with perineural cysts experience symptoms. For those with symptoms, surgery to remove the cysts typically relieves those symptoms, and the cysts rarely recur. Neurological damage can occur in people with symptomatic cysts who do not seek treatment.