Perineural cysts, which are also known as Tarlov cysts, are fluid-filled sacs that form on nerves at the base of the spine. A person with such cysts would likely never know it. They almost never cause symptoms. When they do cause symptoms, however, the most common is pain in the lower back, buttocks, and 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 not often diagnosed. A doctor can determine if a patient has the cysts using imaging techniques. They are often misdiagnosed because perineural cysts that cause symptoms are so rare. These cysts can be drained to provide temporary relief of symptoms. However, only surgery can keep them from coming back or refilling with fluid and producing symptoms again. If not treated, the rare cysts that cause symptoms can produce permanent neurological damage.
A cyst is a sac that can form anywhere in the body and is filled with air or some type of fluid. Most of these are completely benign and noncancerous. Perineural cysts are those that form in the sacrum, or the base of the spine. They form around the roots of nerves in this part of the body. They 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 perineural cysts.
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 with perineural cysts is possible, but very rare.
Why cysts grow in the sacrum is not known, but there are reasons why they may develop into enlarged cysts that cause symptoms. If a person experiences some type of trauma in the relevant area of the back, undiagnosed perineural cysts can begin to fill up with fluid and start producing symptoms. Types of trauma that can trigger symptoms include falls, injuries, and heavy exertion.
Because the vast majority of perineural cysts cause no symptoms, most are never diagnosed. However, a doctor can order imaging tests to identify them when a person experiences symptoms. Magnetic resonance imaging (MRIs) can show cysts. A computed tomography (CT) 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. If a patient exhibits symptoms, however, they may need treatment to relieve the pressure called by the enlarged cysts. 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 probably never have any symptoms or need any treatment. Only one percent of people with perineural cysts experience symptoms (Lucantoni et al., 2011). For those with symptoms, surgery to remove the cysts typically relieves those symptoms and the cysts rarely recur. People with cysts that cause symptoms who do not seek treatment might experience nerve and neurological damage.