Synovial Cysts

Spinal synovial cysts are fluid-filled sacs that develop from the synovial lining of the facet joints in the spine. They most commonly arise at the L4–L5 level and can protrude into the spinal canal, compressing nerve roots and causing pain, numbness, or weakness.

Synovial cysts are a direct consequence of facet joint pathology — they almost always develop in the setting of advanced Facet Disease and are particularly common when Spondylolisthesis is present, as the abnormal spinal motion drives cyst formation. When large, they contribute to Spinal Stenosis and Foraminal Stenosis by occupying space within the spinal canal or neural foramen.

Causes

Facet joint degeneration.

Synovial cysts are strongly associated with degenerative facet joint disease and spinal instability. As facet joints degenerate and become arthritic, excessive joint motion stimulates the synovial lining to produce fluid, which can accumulate and form a cyst. They are therefore most common in older adults with advanced lumbar facet arthritis.

Other contributing factors

Spinal instability from conditions such as degenerative spondylolisthesis significantly increases the risk of synovial cyst formation, as repetitive abnormal motion at the facet joint drives cyst development. Inflammatory arthritis conditions may also predispose individuals to synovial cyst formation throughout the spine.

Symptoms

Small cysts may be entirely asymptomatic. When a cyst grows large enough to compress neural structures, patients may experience lower back pain, sciatica, leg pain, numbness, or weakness following the distribution of the affected nerve root. Bilateral leg symptoms can occur when the cyst significantly compromises the central spinal canal. Symptoms are often worse with prolonged standing or walking and may improve with sitting or flexion.

Diagnosis

Physical examination evaluates for nerve root tension signs and neurological deficits.

Lumbar spine MRI is the definitive imaging tool, clearly showing the cyst as a fluid-filled structure adjacent to the facet joint, often indenting the thecal sac or compressing a nerve root. The signal characteristics of the cyst on MRI help distinguish it from other lesions such as Tarlov Cysts. CT scan may demonstrate calcification within the cyst wall and provides detailed bony anatomy of the affected facet joint.

Classification

Spinal synovial cysts are categorized based on their location relative to the spinal canal and the structures they affect.

• Intraspinal: Cyst protrudes into the spinal canal, compressing the thecal sac or nerve roots.
• Extraspinal/Foraminal: Cyst extends into the neural foramen, compressing the exiting nerve root.
• Bilateral: Cysts arising from both facet joints at the same level, potentially causing central canal compromise.

Treatments

Treatment depends on symptom severity and the degree of neural compression. Asymptomatic cysts found incidentally on imaging do not require treatment.

Conservative measures are typically the first approach for symptomatic cysts with mild to moderate symptoms.

Conservative treatment: Anti-inflammatory medications, activity modification, and physical therapy may help manage symptoms. CT-guided or fluoroscopic cyst rupture and aspiration — in which the cyst is punctured and drained — combined with steroid injection into the facet joint can provide effective relief in many patients, though cysts may recur.

Surgical treatment

When conservative measures fail or when neurological compromise is significant, surgical excision of the cyst through a minimally invasive or open laminotomy approach is highly effective. Because cysts are associated with underlying facet joint instability, spinal fusion may be performed concurrently to prevent recurrence, particularly when degenerative spondylolisthesis is present.

Related Spine Conditions

• Facet Disease
• Spondylolisthesis
• Spinal Stenosis
• Foraminal Stenosis
• Tarlov Cyst
• Back to all Spine Conditions