Facet Synovial Cyst¶
Definition¶
A facet synovial cyst (juxtafacet cyst) is a fluid-filled or gelatinous cyst that arises from the capsule of a degenerated facet joint and extends into the spinal canal. It is a recognized cause of radiculopathy and spinal stenosis, most commonly at L4–L5.
Pathophysiology¶
- Degenerative facet arthropathy → capsular laxity and synovial hypertrophy
- Synovial fluid extrudes through a weakened capsule forming a cyst
- The cyst extends medially into the lateral recess or central canal
- Cyst contents range from clear synovial fluid to hemorrhagic or gelatinous material
- Strongly associated with segmental instability (especially degenerative spondylolisthesis)
Imaging Findings¶
MRI — Primary Modality¶
| Feature | Appearance |
|---|---|
| Location | Posterolateral spinal canal, immediately adjacent to the facet joint |
| T1 signal | Variable — iso to hyperintense (depending on fluid vs hemorrhagic/proteinaceous content) |
| T2 signal | Typically hyperintense (fluid); may be mixed if hemorrhagic |
| Rim | Low-signal rim (calcification or hemosiderin); may enhance with gadolinium |
| Facet joint | Adjacent facet arthropathy — effusion, hypertrophy, often at the same level |
| Neural effect | Compresses traversing nerve root in the lateral recess |
CT¶
- Well-defined, often calcified or partially calcified mass adjacent to the facet joint
- May show communication with the facet joint space
- Calcified rim is characteristic
Clinical Pearl
Facet synovial cysts are strongly associated with segmental instability — approximately 50% of patients with synovial cysts have an associated spondylolisthesis at the same level. The cyst develops because the unstable segment generates excessive motion and synovial hypertrophy. This has treatment implications: simple cyst aspiration/rupture has a high recurrence rate unless the underlying instability is addressed (i.e., fusion). Always check for spondylolisthesis when a synovial cyst is identified.
Key Points¶
- Synovial cysts arise from degenerated facet joints, most commonly at L4–L5
- They extend into the lateral recess or canal, compressing the traversing nerve root
- MRI shows a T2-bright cyst with a low-signal rim adjacent to the facet joint
- Strongly associated with segmental instability and spondylolisthesis
- High recurrence rate after aspiration alone — fusion may be needed if instability is present
References¶
- Gaillard F, et al. Spinal synovial cyst. Radiopaedia.org. https://radiopaedia.org/articles/spinal-synovial-cyst-1
- Apostolaki E, Davies AM, Evans N, Cassar-Pullicino VN. MR imaging of lumbar facet joint synovial cysts. European Radiology. 2000;10(4):615-623. https://pubmed.ncbi.nlm.nih.gov/10795544/
- Abd El-Kader HE. Juxtafacet spinal synovial cysts. Asian Spine Journal. 2016;10(1):46-51. https://pmc.ncbi.nlm.nih.gov/articles/PMC4764539/
- Khan AM, Girardi F. Spinal lumbar synovial cysts. Diagnosis and management challenge. European Spine Journal. 2006;15(8):1176-1182. https://pmc.ncbi.nlm.nih.gov/articles/PMC3233964/
- El Shazly AA, Khattab MF. Surgical excision of a juxtafacet cyst in the lumbar spine: a report of thirteen cases with long-term follow up. Asian Journal of Neurosurgery. 2011;6(2):78-82. https://pmc.ncbi.nlm.nih.gov/articles/PMC3277074/
- Awh MH. Lumbar synovial cyst. MRI Web Clinic. Radsource. February 2006. https://radsource.us/lumbar-synovial-cyst/