Spinal synovial cyst is an intraspinal cystic formation originating from a degenerative facet joint, lined by synovial membrane, containing synovial fluid or hemorrhagic content. L4-5 is the most commonly affected level (65-70%), followed by L5-S1 and L3-4. The cyst protrudes from the medial aspect of the facet joint into the posterior epidural space at the level of the ligamentum flavum and can grow toward the spinal canal causing thecal sac and/or nerve root compression. On MRI T2-weighted sequences, it appears as a hyperintense cystic lesion; capsular rim enhancement on contrast MRI is typical. Hemorrhagic variant may show T1 hyperintensity (methemoglobin). Calcified synovial cyst shows hyperdense ring on CT. Facet joint degeneration (effusion, osteophytes, hypertrophy) almost always accompanies. Clinically can cause radiculopathy, neurogenic claudication, and rarely cauda equina syndrome. Asymptomatic cysts may be incidental findings. Treatment options: conservative observation (asymptomatic), CT-guided aspiration + steroid injection (50-75% success rate), and surgical resection (most definitive treatment, 85-95% success).
Age Range
50-80
Peak Age
65
Gender
Equal
Prevalence
Uncommon
Synovial cysts are a complication of facet joint degeneration. Pathogenesis: facet joint degeneration → capsular laxity + synovial inflammation → increased synovial fluid production + elevated intra-articular pressure → synovial membrane herniates through capsular weak point (usually medial aspect) → cyst forming toward posterior epidural space. Cyst wall is lined by synovial membrane (true synovial cyst) or lacks synovial membrane (ganglion cyst — pseudocyst). Both types behave similarly clinically and radiologically. L4-5 being the most common level is because this segment experiences the most flexion-extension motion and is the most common level for degenerative spondylolisthesis-associated instability. Cyst content: clear synovial fluid (simple cyst) → T1 hypointense, T2 hyperintense because synovial fluid is free-water based → long T2. Hemorrhagic cyst: intracystic hemorrhage → methemoglobin accumulation → T1 hyperintensity (methemoglobin paramagnetic effect → T1 shortening). Capsular enhancement: vascularity of synovial membrane in cyst wall → gadolinium accumulation → rim enhancement. Calcification: calcium deposition in cyst wall in chronic cysts → hyperdense ring on CT, hypointense rim on MRI.
T2 hyperintense cystic lesion in the posterolateral epidural space with continuity to the facet joint — pathognomonic finding of spinal synovial cyst. Confirms the cyst originates from the facet joint and its content is synovial fluid. Diagnosis is confirmed with rim enhancement on contrast MRI.
Hyperintense (fluid signal) cystic lesion in the posterolateral epidural space with continuity to facet joint on T2-weighted MRI. Oval or lobulated morphology, well-defined, thin-walled. Located at ligamentum flavum level and protrudes toward the spinal canal. Simple synovial cyst is homogeneously T2 hyperintense; hemorrhagic or proteinaceous content may show heterogeneous signal or fluid-fluid level on T2. Thecal sac and/or nerve root compression is evaluated.
Report Sentence
T2 hyperintense cystic lesion in the posterolateral epidural space with continuity to the __[left/right] facet joint at __ level, consistent with synovial cyst; __[mild/moderate/significant] mass effect on thecal sac.
Hyperintense appearance of cyst content on T1-weighted MRI — characteristic finding of hemorrhagic synovial cyst. While simple synovial cyst is T1 hypointense (water signal), methemoglobin accumulation after intracystic hemorrhage produces T1 hyperintensity (bright signal). Hemorrhagic cyst may also be T2 hyperintense (free methemoglobin) or show heterogeneous signal (hemorrhage products of different ages). This finding indicates the cyst is not simple and has undergone hemorrhagic complication.
Report Sentence
Posterolateral epidural cystic lesion at __ level showing T1 hyperintense signal, consistent with hemorrhagic synovial cyst.
Thin capsular rim enhancement around the cyst on contrast MRI — typical enhancement pattern of synovial cyst. Cyst content does not enhance (avascular fluid), vascularized synovial membrane in cyst wall enhances → ring-shaped peripheral enhancement. This pattern is important in differential diagnosis from epidural abscess (thick irregular rim + clinical infection) and solid tumor (homogeneous/heterogeneous solid enhancement).
Report Sentence
Thin capsular rim enhancement around posterolateral epidural cystic lesion at __ level on contrast MRI, consistent with synovial cyst.
Hyperdense-walled cystic lesion in the posterior epidural space at facet joint level on CT — calcified synovial cyst. Calcium deposition develops in the cyst wall of chronic synovial cysts. CT demonstrates calcification much better than MRI. Cyst wall appears as hyperdense ring, cyst content at soft tissue or water density. Accompanying facet degeneration (osteophytes, sclerosis) is present.
Report Sentence
Calcified-walled cystic lesion in the posterior epidural space at __[left/right] facet joint level at __ on CT, consistent with calcified synovial cyst.
Synovial cyst protruding into the spinal canal causing thecal sac and/or nerve root compression. On axial T2, the cyst displaces the thecal sac contralaterally and/or compresses the traversing nerve root. Cyst size generally correlates with clinical symptom severity. Large cysts may also contribute to central stenosis.
Report Sentence
Posterolateral epidural synovial cyst at __ level __[left/right] causing mass effect on thecal sac and compressing the __[traversing/exiting] nerve root.
Criteria
Clear synovial fluid content, T1 hypointense, T2 homogeneously hyperintense, thin regular wall
Distinct Features
Most common variant. CSF-like signal. Better response to aspiration + steroid injection
Criteria
Intracystic hemorrhage, T1 hyperintense (methemoglobin), T2 heterogeneous, may have fluid-fluid level
Distinct Features
May present acutely (sudden symptom onset). T1 hyperintensity strengthens diagnosis. Lower response to aspiration (thick content)
Criteria
Wall calcification, hyperdense ring on CT, hypointense rim on MRI
Distinct Features
Seen in chronic cysts. CT complementary in diagnosis. Aspiration may be difficult (thick calcified wall). Surgical resection preferred
Distinguishing Feature
Disc herniation is solid/intermediate signal structure originating from disc level; synovial cyst is T2 hyperintense cystic morphology with facet joint continuity
Distinguishing Feature
Facet arthropathy is diffuse joint degeneration (effusion stays within joint); synovial cyst is cystic formation protruding outside the joint
Distinguishing Feature
Spinal stenosis is diffuse canal narrowing; synovial cyst is focal cystic lesion that may contribute to stenosis but primary pathology is the cyst itself
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
6-monthAsymptomatic synovial cysts require no treatment — followed as incidental finding. Treatment steps for symptomatic cysts: conservative (NSAIDs, physical therapy) → CT-guided aspiration + steroid injection (50-75% success, high recurrence rate) → surgical resection (most definitive treatment, 85-95% success, removed with facet joint). Decompression + fusion may be required if instability is present. Cauda equina syndrome requires emergency surgery. Spontaneous regression has been rarely reported — mechanism is cyst rupture or synovial fluid resorption.
When symptomatic, synovial cysts can cause radiculopathy, neurogenic claudication, or cauda equina syndrome. No treatment needed for asymptomatic cysts. Options for symptomatic cases: CT-guided aspiration + steroid injection (variable success rate), surgical resection (most definitive treatment, removed with facet joint). Spontaneous regression has been rarely reported. Decompression + fusion may be required if instability is present.