Synovial Cyst of the Spine

What is a spinal synovial cyst?

Each vertebra connects to its neighbors through two facet joints at the back. Like other synovial joints, they are lined by synovium, which makes lubricating fluid. When the joints wear down with arthritis, the capsule weakens, and joint fluid can bulge out into a sac. This is a synovial cyst.

The cyst usually pushes into the spinal canal or the side opening where a nerve root exits (the foramen). Because it sits next to the nerves, even a cyst 1 to 2 cm across can compress them. Cysts can fill with blood or harden with calcium, which may make symptoms worse suddenly.

Synovial cysts elsewhere in the body are common too, such as a Baker's cyst behind the knee or a ganglion cyst at the wrist. This page covers cysts of the spine.

Causes and risk factors

• Facet joint arthritis: the main cause. See facet joint syndrome
• Degenerative spondylolisthesis: a vertebra slipping forward on the one below, which strains the facets; frequently found with synovial cysts at L4-L5
• Instability or excess motion at a spinal level
• Age: most people are in their 60s or older
• Previous back injury or surgery at the same level

Symptoms of a synovial cyst

Many cysts cause no symptoms. When they do:

• Low back pain, often aching and worse with standing or arching back
• Radiating leg pain (sciatica) down the buttock and leg, usually on the side of the cyst, sometimes into the foot
• Numbness, tingling or weakness in the leg or foot in the area supplied by the compressed nerve
• Neurogenic claudication: heaviness, cramping or pain in the legs when walking or standing, relieved by sitting or bending forward. This happens when the cyst adds to spinal stenosis
• Rarely, sudden severe symptoms if the cyst bleeds

Cysts in the neck can cause arm pain, numbness or, rarely, spinal cord compression with clumsy hands and unsteady walking.

Synovial cyst vs herniated disc

Both cause similar nerve root symptoms, and only imaging reliably distinguishes them.

How it is diagnosed

• History and neurological exam: checking strength, reflexes and sensation in the legs, and nerve tension tests such as the straight leg raise.
• MRI: the best test. It shows the cyst as a round, fluid-filled structure next to the facet joint and how much it compresses the nerves.
• CT scan: useful if MRI is not possible, or to see calcification of the cyst wall.
• Standing or flexion-extension X-rays: check for spondylolisthesis and instability, which affect surgical planning.

Treatment

Nonsurgical treatment

Symptoms sometimes improve without surgery, and occasionally cysts shrink on their own.

• Activity modification and physical therapy: flexion-based exercises, core strengthening and walking with a forward lean or using a stationary bike
• Medicines: NSAIDs at the label dose for short periods; medicines for nerve pain
• Epidural steroid injection: reduces nerve inflammation and can relieve leg pain for weeks to months
• Facet joint injection and cyst rupture: under X-ray guidance, fluid and steroid are injected into the joint to burst the cyst. This works for some people, but cysts can refill and many still need surgery later

Surgery

Surgery is recommended for persistent, disabling pain after several weeks to months of nonsurgical care, progressive weakness, or signs of cauda equina syndrome.

• Decompression with cyst removal: laminectomy or a smaller laminotomy removes bone and the cyst to free the nerves. Results for leg pain are good in most patients.
• Decompression with fusion: added when there is spondylolisthesis or instability, because decompression alone at an unstable level carries a higher risk of the cyst returning and the slip worsening.

Recovery after decompression usually allows walking the same or next day and return to light activity within a few weeks; fusion takes longer.

Outlook

Most people improve with treatment. Surgery relieves leg pain in a large majority, with low recurrence when the cyst and source are fully addressed. Back pain from underlying arthritis may persist and is managed with exercise and activity pacing.

Frequently asked questions

What are the symptoms of a synovial cyst in the spine?

Common symptoms are lower back pain and pain shooting down one leg, often with numbness, tingling or weakness. Many people feel leg heaviness or cramping when walking or standing that eases with sitting or bending forward. Small cysts often cause no symptoms at all.

Can a spinal synovial cyst go away on its own?

Occasionally. Some cysts shrink or rupture spontaneously, and symptoms often settle with physical therapy and injections. However, many persist because the underlying joint arthritis remains. Ongoing or worsening nerve symptoms usually lead to surgery.

Is a synovial cyst serious?

It is benign and not cancerous. It becomes serious only if it presses hard enough on nerves to cause progressive weakness or, rarely, cauda equina syndrome with bladder or bowel problems. These need urgent assessment and usually surgery.

What is the best treatment for a lumbar synovial cyst?

It depends on symptoms. Mild cases improve with physical therapy, pain relief and epidural injections. Cyst rupture by injection helps some people. For persistent or severe pain, surgical removal of the cyst with decompression, plus fusion if the spine is unstable, gives the most reliable long-term relief.