Spinal synovial cysts occur when the fluid that normally lubricates the inner lining of joints (synovium) builds up and forms a sac. This is usually a result of degenerative changes or trauma. Spinal synovial cysts are relatively rare and usually asymptomatic for most individuals.
Spinal synovial cysts typically occur in the facet joints (the junction of the "railroad track" that keeps the vertebrae interlocked). While they can occur anywhere in the spine, they are most often found in the lumbar region (low back) in about 90% of cases.
For the majority of individuals, synovial cysts won't cause any symptoms. Others may experience back pain, weakness, or numbness if the synovial cyst is causing nerve compression.
Synovial cysts can occur on one side of the spine or both, and they can occur at one spinal segment or at multiple levels. The severity of a person's symptoms depends on both the size and the location of the cyst.
If a spinal synovial cyst comes in contact with or presses on the spinal nerve root, symptoms of radiculopathy (pinched nerve) may occur, which can manifest as sciatica or weakness, numbness, or difficulty controlling specific muscles. Other symptoms of spinal synovial cysts include neurogenic claudication (impingement and inflammation of spinal nerves), which causes cramping, pain, and/or tingling in the low back, legs, hips, and buttocks.1
More rarely, symptoms related to cauda equina may arise from nerve impingement, which include bowel and/or bladder problems, progressive leg weakness, and saddle anesthesia, characterized as a loss of sensation in the inner thighs, buttocks, and perineum.
Synovial cysts in the mid-back and neck are rare. When they do occur, thoracic synovial cysts and cervical synovial cysts may cause a range of symptoms that fall under the broad term myelopathy—problems with the spinal cord resulting in numbness and weakness.2
Most spinal synovial cysts occur in the lumbar region at vertebrae L4 or L5. For a point of reference, L4 and L5 are located at a level right below the belly button. This area is considered to have a significant amount of spinal instability, which may be related to the formation of cysts.
Spinal synovial cysts are generally caused by one of the following:
Degenerative changes like osteoarthritis that may develop in a joint over time
Trauma (minor or significant), such as a slip and fall, car accident, or sports injury
With wear and tear, facet joint cartilage (the springy material in a joint that provides protection and shock absorption) erodes. In the process, the lining of the joint (synovium) may form a cyst.
Traumas both large and small have degenerative and inflammatory effects on joints as well, which may result in the formation of a synovial cyst.
About a third of patients who have a spinal synovial cyst also have a condition known as spondylolisthesis, which is when a lower vertebra slips forward onto the bone underneath it. It's thought that spondylolisthesis causes synovial cysts to form due to decreased stability in the facet joint.
Cysts are generally diagnosed via magnetic resonance imaging (MRI).3 Practitioners may also diagnose a spinal synovial cyst via ultrasound, X-ray, or computed tomography (CT) scan.
Some cysts remain small and present few symptoms. Other than regular monitoring and lifestyle changes, these cysts may not need treatment. In other cases, medical intervention may be required. 3
Doctors may suggest avoiding certain activities that aggravate symptoms and replacing them with stretching and types of mild to moderate physical activity that do not exacerbate your condition. Physical therapy or occupational therapy may also be recommended.
Intermittent use of over-the-counter nonsteroidal anti-inflammatories (NSAIDs) like Advil (ibuprofen) and Aleve (naproxen) may also help relieve occasional pain.
For cysts that cause significant pain, numbness, weakness, and other issues, an aspiration procedure to drain fluid from the cyst may be a sufficient course of action for some people.
In one study, researchers found that the success rate for these procedures ranges from 0% to 50%. People who undergo aspiration often need repeat procedures as the fluid build-up may return.
Epidural corticosteroid injections might be another suitable option to relieve significant pain. However, it's recommended that patients receive no more than three corticosteroid injections per year.
For more extreme or persistent cases, doctors may recommend undergoing decompression surgery to remove the cyst and surrounding bone, which should relieve pressure on the nerve root.
There are several surgical options that range from minimally invasive endoscopic procedures to more severe open surgeries. The best surgical option for each patient varies based on the severity of their situation and whether associated disorders are present.
Laminectomy, the surgical removal of the bony structure that covers the spinal canal (lamina), is one option. Hemilaminectomy, a modified laminectomy procedure where a smaller portion of the lamina is removed, is another common option.
Either of these procedures may be accompanied by a facetectomy to remove part of the affected facet joint where the synovial cyst is located. Fusion of the facet joints and vertebra (to decrease mobility in the area) may or may not be performed.
Most people experience immediate pain relief following either a laminectomy or hemilaminectomy. Fusion cites can take six to nine months to heal.
However, if the surgery was performed without fusion of the joints where the cyst originated, the pain may return and another cyst may form within two years.
These surgeries are not without risk. Complications may include infection, bleeding, and injury to the spinal cord or nerve root.
A Word from Verywell
If spinal synovial cysts are causing symptoms, it's important to seek medical advice because they may herald more serious conditions such as degenerative disc disease, spinal stenosis, or cauda equina syndrome.