What is Synovial Cyst of the Spine?
A synovial cyst is a benign, fluid-filled sac that develops from a degenerating facet joint, most often in the lumbar spine. As the cyst enlarges it can press on adjacent nerve roots, producing symptoms much like stenosis or a herniated disc: back pain, leg pain, and numbness when standing or walking.
Because these cysts arise from arthritic joints, they rarely resolve on their own. Options include image-guided aspiration and, definitively, a minimally invasive decompression to remove the cyst — sometimes combined with fusion when the underlying joint is unstable.
Common symptoms
Why it happens
An arthritic facet joint produces excess fluid, which balloons out of the joint capsule as a cyst — almost always at L4-5, the most mobile lumbar level. The cyst occupies canal space and compresses the adjacent nerve root.
How it is diagnosed
MRI shows a characteristic fluid-filled sac arising from the facet joint. Standing X-rays are essential: cysts signal an arthritic, sometimes unstable joint, and detecting slippage changes the treatment plan.
Treatment options
Image-guided aspiration or joint injection helps some patients, though cysts often recur because the arthritic joint remains. Definitive treatment is minimally invasive removal of the cyst with decompression of the nerve; fusion is added only when the joint is demonstrably unstable.
