A lumbar synovial cyst, also called a facet cyst, is a fluid-filled sac that develops next to one of the facet joints in the lower back.
Facet joints are small joints located along the back of the spine. They help guide movement and provide stability. When these joints become arthritic or unstable, the joint lining can produce excess fluid and form a cyst.
A lumbar facet cyst may cause no symptoms at all. However, if it grows into the spinal canal or neural foramen, it can compress nearby nerves and cause leg pain, numbness, weakness, or difficulty walking.
What Causes a Lumbar Synovial Cyst?
Lumbar synovial cysts are usually associated with degeneration of the facet joints.
As the joint becomes arthritic, several changes may occur:
- Cartilage wears down
- The joint enlarges
- Bone spurs develop
- The joint capsule becomes stretched
- Excess joint fluid accumulates
- Abnormal motion may develop
A cyst can form when fluid from the degenerative facet joint extends outward through a weakened portion of the joint capsule.
These cysts are most commonly seen in older adults.
Where Do Lumbar Facet Cysts Usually Occur?
Facet cysts can occur at any lumbar level, but they are especially common at L4-L5.
This level is one of the most mobile segments of the lumbar spine and is also a common location for:
- Facet arthritis
- Degenerative spondylolisthesis
- Spinal stenosis
- Segmental instability
For this reason, a facet cyst may be one part of a broader degenerative process rather than an isolated problem.
Symptoms of a Lumbar Synovial Cyst
Symptoms depend on the size and location of the cyst and which nerve is compressed.
Possible symptoms include:
- Low-back pain
- Buttock pain
- Leg pain
- Numbness or tingling
- Leg weakness
- Heaviness in the legs
- Difficulty walking
- Symptoms that worsen with standing or walking
Some patients have symptoms similar to a herniated disc.
Others develop symptoms more typical of lumbar spinal stenosis.
Lumbar Radiculopathy
When a facet cyst compresses an individual nerve root, it can cause lumbar radiculopathy.
Symptoms may include:
- Shooting pain down the leg
- Burning pain
- Numbness
- Tingling
- Weakness in a specific muscle group
The exact pattern depends on which nerve root is affected.
A cyst at L4-L5, for example, commonly compresses the L5 nerve root.
Neurogenic Claudication
If the cyst contributes to central spinal stenosis, patients may develop neurogenic claudication.
Symptoms can include:
- Leg heaviness
- Numbness
- Weakness
- Aching
- Reduced walking tolerance
These symptoms often worsen when standing or walking and improve when sitting or leaning forward.
Can a Facet Cyst Change in Size?
Yes.
Because many facet cysts communicate with the facet joint, their size can sometimes change over time.
Symptoms may therefore fluctuate.
A cyst may occasionally:
- Enlarge
- Shrink
- Rupture
- Hemorrhage
- Become more symptomatic
Although spontaneous resolution can occur, persistent nerve compression often requires treatment.
Hemorrhage Into a Facet Cyst
Rarely, bleeding can occur inside a synovial cyst.
A hemorrhagic cyst may enlarge suddenly and cause more abrupt symptoms.
These can include:
- Sudden severe leg pain
- Rapidly worsening numbness
- Weakness
- Acute nerve compression
This is less common than the gradual development of symptoms.
How Is a Lumbar Synovial Cyst Diagnosed?
MRI is usually the most useful imaging study.
MRI
MRI can show:
- The facet cyst
- Its relationship to the facet joint
- Nerve root compression
- Spinal stenosis
- Disc degeneration
- Facet arthritis
- Spondylolisthesis
A synovial cyst usually appears as a well-defined fluid-filled structure next to the facet joint.
CT Scan
CT can provide additional information about:
- Facet joint arthritis
- Bone spurs
- Calcification of the cyst wall
- Spinal anatomy
- Previous surgery
CT may also be useful when planning injections or surgery.
Standing X-Rays
Standing X-rays may be obtained to evaluate:
- Degenerative spondylolisthesis
- Disc space collapse
- Spinal alignment
- Instability
Flexion-extension X-rays may sometimes be used to look for abnormal movement at the affected level.
This can be particularly important when deciding whether decompression alone is sufficient or whether fusion should also be considered.
Nonsurgical Treatment
Initial treatment may include:
- Activity modification
- Anti-inflammatory medications
- Pain medications
- Physical therapy
- Epidural steroid injections
- Facet injections
These treatments may reduce inflammation and improve symptoms but do not always eliminate the cyst itself.
Epidural Steroid Injection
An epidural steroid injection may reduce inflammation around the compressed nerve.
This can provide temporary relief of:
- Leg pain
- Numbness
- Radicular symptoms
However, the cyst remains present, so symptoms may return.
Facet Joint Injection and Cyst Rupture
In selected patients, an image-guided procedure may be used to inject the facet joint and attempt to rupture the cyst.
During the procedure, fluid or contrast is placed under pressure into the facet joint.
If the cyst communicates with the joint, it may rupture and decompress.
This can sometimes provide meaningful relief without surgery.
However:
- The cyst may not rupture
- Symptoms may persist
- The cyst may recur
- Associated spinal stenosis may remain
For this reason, cyst rupture is not successful in every patient.
When Is Surgery Considered?
Surgery may be considered when:
- Leg pain remains severe
- Numbness or weakness is progressing
- Walking becomes significantly limited
- Symptoms persist despite nonsurgical treatment
- The cyst causes significant spinal stenosis
- Neurologic dysfunction develops
The goal of surgery is to remove or decompress the cyst and relieve pressure on the affected nerves.
Lumbar Decompression and Cyst Removal
The most common operation involves decompression of the affected nerve.
This may include:
- Laminotomy
- Laminectomy
- Medial facetectomy
- Foraminotomy
- Removal of the cyst
The cyst is typically carefully separated from the surrounding nerve structures.
In some cases, the cyst may be densely attached to the dura or nerve root, requiring careful dissection.
Is Fusion Always Necessary?
No.
Many lumbar synovial cysts can be treated with decompression and cyst removal alone.
However, fusion may be considered when there is significant instability.
Factors that may favor fusion include:
- Degenerative spondylolisthesis
- Abnormal motion on flexion-extension X-rays
- Significant facet joint destruction
- Need for extensive facetectomy
- Recurrent cyst after previous decompression
- Significant mechanical back pain associated with instability
The decision should be individualized rather than assuming every facet cyst requires fusion.
Why Are Facet Cysts Associated With Spondylolisthesis?
Facet cysts often occur in joints that have become both arthritic and excessively mobile.
That same abnormal motion can allow one vertebra to slip relative to another.
This is called degenerative spondylolisthesis.
For this reason, a facet cyst may be a sign of underlying segmental instability.
However, the presence of a cyst does not automatically mean the segment is unstable enough to require fusion.
Minimally Invasive Surgery
Some lumbar facet cysts can be treated using minimally invasive decompression techniques.
Potential advantages may include:
- Smaller incision
- Less muscle disruption
- Reduced blood loss
- Shorter hospital stay
- Faster early recovery
The most important goal is complete nerve decompression while preserving as much spinal stability as possible.
Recovery After Surgery
Recovery depends on whether the procedure involves decompression alone or decompression with fusion.
After decompression alone, many patients are encouraged to begin walking soon after surgery.
Leg pain may improve quickly once the nerve is decompressed.
Numbness and weakness can take longer to recover, particularly if the nerve has been compressed for an extended period.
Fusion generally requires a longer recovery.
Can a Synovial Cyst Come Back?
Yes.
Recurrence is possible after decompression or cyst rupture.
The risk may be higher when the underlying facet joint remains significantly arthritic or unstable.
Recurrence is one factor considered when deciding whether fusion should accompany cyst removal.
Cauda Equina Syndrome
Rarely, a very large facet cyst can severely compress the nerves of the cauda equina.
Symptoms may include:
- Severe or rapidly progressive leg weakness
- Saddle numbness
- Urinary retention
- Loss of bladder control
- Bowel dysfunction
These symptoms require urgent medical evaluation.
When Should a Lumbar Facet Cyst Be Evaluated Promptly?
Prompt evaluation is appropriate for:
- New or progressive weakness
- Rapidly worsening numbness
- Severe walking difficulty
- Saddle anesthesia
- Urinary retention
- New bowel or bladder dysfunction
These symptoms may indicate significant nerve compression.
Outlook
Lumbar synovial cysts are usually caused by degeneration of the facet joints and most commonly occur at L4-L5.
Some cysts cause no symptoms and require no treatment.
When a cyst compresses a nerve, treatment may include:
- Medications
- Physical therapy
- Epidural injections
- Facet joint injection with attempted cyst rupture
- Surgical decompression
- Cyst removal
- Fusion when significant instability is present
Treatment should be based on the combination of:
- Symptoms
- Neurologic examination
- Degree of nerve compression
- Spinal stenosis
- Presence of spondylolisthesis
- Segmental instability
- Patient goals
The primary goal is to relieve nerve compression while preserving spinal stability whenever possible.
Related Topics
- Lumbar Spinal Stenosis
- Lumbar Radiculopathy
- Degenerative Spondylolisthesis
- Facet Joint Arthritis
- Lumbar Foraminal Stenosis
- Lumbar Laminectomy
- Lumbar Foraminotomy
- Lumbar Spinal Fusion
- Cauda Equina Syndrome