Lumbar Synovial Cyst
A fluid-filled cyst arising from a degenerated lumbar facet joint
ICD-10: M51.9 · lumbar condition
A lumbar synovial cyst is a fluid-filled sac that develops from the synovial lining of a degenerated facet joint in the lumbar spine. As the facet joint degenerates, excess synovial fluid can accumulate and be forced through the joint capsule, forming a cyst in the spinal canal or neural foramen. These cysts most commonly occur at L4–L5 — the most mobile and stress-bearing lumbar segment — and may compress adjacent nerve roots, causing radiculopathy, or (rarely) the spinal canal, contributing to stenosis. Synovial cysts are almost exclusively a degenerative condition and are closely associated with lumbar facet arthropathy and segmental instability.
70–80%
Lumbar synovial cysts occur most commonly at L4–L5, accounting for approximately 70–80% of cases, reflecting the high mobility and degeneration rate at that level.
North American Spine Society80–95%
Surgical excision achieves meaningful leg pain relief in 80–95% of patients with symptomatic lumbar synovial cysts.
Martha JF et al., Journal of Neurosurgery Spine (2009)Symptoms
- Low back pain localized to the affected facet joint level
- Leg pain, numbness, or weakness (radiculopathy) if the cyst compresses a nerve root
- Neurogenic claudication if the cyst narrows the spinal canal
- Pain that may worsen with extension and improve with flexion
- In rare cases, cauda equina symptoms from large cysts obstructing the thecal sac
Causes & Risk Factors
- Lumbar facet joint degeneration and arthritis (primary driver)
- Segmental instability — abnormal motion at a spinal level promotes cyst formation
- Spondylolisthesis — forward slippage at L4–L5 creates shearing forces on the facet joint
- Age — synovial cysts are predominantly a condition of adults over 50
Treatment Options
Conservative
- NSAIDs and analgesics for pain management
- Physical therapy — core strengthening and lumbar stabilization exercises
- Facet joint corticosteroid injection — may reduce cyst size and relieve pressure on the nerve
- CT-guided cyst aspiration and steroid injection — the most targeted conservative approach
Surgical
- Laminotomy and cyst excision — the most definitive treatment; removes the cyst directly
- Lumbar fusion — often added when significant instability is present at the cyst level
When to see a spine specialist
See a spine specialist if you have lumbar radiculopathy (leg pain, numbness, or weakness) that is not improving with conservative care, or if MRI has identified a synovial cyst. Urgent evaluation is needed for any signs of cauda equina syndrome — bilateral leg weakness, saddle numbness, or bladder/bowel dysfunction.
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Search spine specialists →Frequently Asked Questions
Can a synovial cyst go away on its own?
Spontaneous resolution of lumbar synovial cysts has been reported but is uncommon — estimated to occur in approximately 10–20% of cases. The majority of cysts persist or enlarge over time as the underlying facet degeneration progresses. CT-guided facet joint injection may cause cyst rupture and resolution in some patients, providing a non-surgical option before committing to surgery.
What is the difference between a synovial cyst and a ganglion cyst?
Both form adjacent to joints and contain viscous fluid, but they differ in lining: synovial cysts are lined by synovial cells (the same cells that line the joint itself), while ganglion cysts have no cellular lining. Both can occur at lumbar facet joints. In practice, the distinction is often academic — both present with similar symptoms and are treated the same way. "Facet cyst" is sometimes used as a general term encompassing both.
Is surgery effective for lumbar synovial cysts?
Surgical excision of lumbar synovial cysts is highly effective at relieving the radiculopathy caused by nerve root compression. Most studies report 80–95% of patients achieve meaningful leg pain relief after surgical excision. Adding fusion to the procedure (when instability is present) reduces the rate of cyst recurrence but adds surgical complexity. Without fusion, cyst recurrence rates are estimated at 5–10% over 5 years.