Endoscopic Synovial Cyst Excision

The facet joints at the back of the spine are lined by a thin membrane called the synovium, which produces the fluid that lubricates the joint. As a facet joint degenerates, this lining can herniate outward and form a synovial cyst — a sac with a true synovial lining, filled with joint fluid. When the cyst grows into the spinal canal or the lateral recess, it presses on a nerve root, producing leg pain, pins and needles, numbness or weakness, and sometimes contributing to canal narrowing and claudication. Synovial cysts are the classic example of a "juxtafacet" cyst, and, like facet cysts generally, they are a sign of a worn and sometimes slightly unstable joint — which matters greatly when planning treatment.

Where a symptomatic synovial cyst has not settled with non-operative measures, the operation excises it and frees the nerve. Done endoscopically, the endoscope is passed through the interlaminar window to the level of the cyst under continuous irrigation and magnified vision. The cyst, sitting between the facet joint and the nerve, is carefully dissected free of the nerve and the dura — to which a synovial cyst can be firmly adherent — and removed in as complete a fashion as possible, and the nerve is confirmed decompressed. Because the endoscopic approach is a targeted keyhole, only the small amount of bone and joint needed to reach and remove the cyst is disturbed, helping to preserve the segment's stability.

As with facet cysts generally, the central decision is whether to excise the cyst alone or to add a fusion, and I make it individually. A synovial cyst reflects a degenerate, sometimes unstable facet joint, so there is a recognised chance of recurrence, or of ongoing symptoms from the underlying instability, if the cyst is simply removed. For a stable level, endoscopic excision alone gives excellent relief and spares the patient a fusion. Where there is a genuine, mobile slip at the level, adding a fusion removes the abnormal movement that drove the cyst and markedly lowers the chance of recurrence. Weighing stability, symptoms and imaging to make that call is exactly the kind of judgement good practice requires.

The particular challenge with a synovial cyst is that it can be densely adherent to the dura, the delicate lining around the nerves, so separating it cleanly through a small window without tearing that lining is where magnified endoscopic vision and experience count most. Removing enough of the cyst and the offending part of the joint to free the nerve while preserving stability, and recognising when a level's instability means a fusion should be added, are the anatomy-led, individualised decisions that subspecialty endoscopic practice is built on.

The evidence supports minimally invasive and endoscopic excision of synovial cysts as effective and safe. Systematic reviews of minimally invasive synovial cyst excision report good symptom relief with low complication rates, and endoscopic series — including uniportal procedures under local anaesthesia, contralateral biportal approaches, and reports of complete resection of large and giant cysts without the need for fusion — describe successful removal with the tissue-sparing benefits of a keyhole. The recurrence question is documented honestly: recurrence after decompression-only is low but higher where there is instability, whereas adding fusion essentially removes recurrence at the cost of a larger operation. This balanced picture is how I counsel patients.

Because the operation is a targeted keyhole that spares the muscles and most of the joint, recovery is usually quick — many people go home the same day or the next, walking, with early relief of the leg pain as the nerve is freed. Some temporary nerve sensitivity can occur early and usually settles; numbness may take longer to recover. Where a fusion has been added for instability, recovery follows that of a fusion. The spine is followed up over the longer term.

• —Outcomes and complications following minimally invasive excision of synovial cysts of the lumbar spine: systematic review and meta-analysis. (PMID 33984755)
• —Decompression with or without fusion for lumbar synovial cysts: systematic review and meta-analysis. (PMC10095101)
• —Variability of lumbar facet joint synovial cyst recurrence after decompression-only versus decompression/fusion. (PMID 31453836)
• —Full endoscopic resection of giant synovial cyst in the lumbar spine: case report. (PMID 40092242 / PMC11907119)
• —Full endoscopic resection of large bilateral synovial cysts in the lumbar spine. (PMC11013375)
• —Contralateral sublaminar biportal endoscopic removal of lumbar juxtafacet cysts: technical report. (PMID 30458327)