Synovial Cyst of the Spine on Radiology Reports: What It Means

A “synovial cyst of the spine” is a benign (non-cancerous) finding that relates to normal wear and tear in the joints of your spine. MRI helps with diagnosing synovial cysts and how they might relate to your symptoms.  This article explains, in plain language, what a synovial cyst is, how it looks on spine MRI, and what it may mean for your back or leg pain.

What Is a Synovial Cyst in the Spine?

A synovial cyst in the spine is a small, fluid-filled sac that forms next to a facet joint. Facet joints are the small joints at the back of your spine that help it bend and twist smoothly. They are lined with a thin membrane called synovium, which makes joint fluid for lubrication.

Over time, with arthritis and age-related changes, the capsule of the facet joint can weaken. Fluid and joint lining can bulge out, forming a little “pouch” or cyst next to the joint. That is a synovial cyst.

Important points:

• It is usually degenerative, meaning related to wear-and-tear arthritis.

• It is not a tumor and not a sign of cancer.

• It often occurs in the lumbar spine (lower back), especially at L4–L5, where motion and stress are greatest.

Why Are Synovial Cysts Seen on MRI?

MRI is very good at showing soft tissues, fluid, and nerves. Synovial cysts are filled with joint fluid or thickened gelatinous material, so they stand out clearly on MRI images.

Your doctor may order an MRI for:

• Low back pain

• Leg pain, numbness, or weakness (sciatica-like symptoms)

• Trouble walking long distances due to pain or heaviness in the legs

• Suspected spinal stenosis (narrowing of the spinal canal)

An MRI allows detailed pictures of the vertebrae, discs, nerves, and joints. A synovial cyst will usually show up as a small, rounded structure next to a facet joint, often pushing into the spinal canal or the opening where a nerve exits.

How a Synovial Cyst Looks on MRI

Radiologists look at multiple MRI sequences (different “types” of images) to characterize a synovial cyst. In simple terms, a synovial cyst often has these features:

• Location

  • Right next to a facet joint at the back of the spine

  • Common in the lower lumbar levels (L3–L4, L4–L5, L5–S1)

• Shape

  • Usually round or oval

  • Can be small, just a few millimeters, or larger and more complex

• Signal on MRI (how bright or dark it looks)

  • On T2-weighted images (fluid-sensitive), the cyst is often bright, because it contains fluid.

  • On T1-weighted images, it may be dark or intermediate, depending on the protein or blood content inside the cyst.

  • If there has been minor bleeding or high protein content, parts of the cyst may look brighter on T1.

• Wall and rim

  • Often has a thin wall that may enhance (light up) after contrast injection.

  • Sometimes shows a dark rim from calcification or a fibrous capsule.

• Effect on nearby structures

  • May narrow the spinal canal or the nerve root canal (foramen).

  • Can compress a nerve root, which can match up with your symptoms (for example, right-sided leg pain if on the right).

Associated Spinal Changes on MRI

Synovial cysts rarely appear in isolation. They often occur along with other signs of spine wear-and-tear:

• Facet joint arthritis (facet arthropathy)

  • Worn cartilage, bony overgrowth (spurs), and fluid in the joint

  • Irregular joint surfaces and thickened joint capsule

• Degenerative disc disease

  • Loss of disc height

  • Darker discs on MRI (desiccation)

  • Sometimes disc bulges or herniations

• Spinal stenosis

  • Narrowing of the spinal canal because of disc bulging, facet joint overgrowth, thickened ligaments, and the cyst itself

Symptoms Related to a Synovial Cyst

On imaging, a synovial cyst may look dramatic, but not every cyst causes symptoms. Many are found by accident when MRI is done for another reason.

Possible symptoms when a synovial cyst does matter:

• Low back pain

  • Aching or stiffness in the lower back

  • Often related to arthritis in the facet joints

• Leg pain, numbness, or tingling

  • Pain radiating down the buttock and leg (sciatica-type pain)

  • Numbness, tingling, or burning in a specific nerve distribution

• Weakness or heaviness in the leg

  • Sometimes due to more severe nerve compression

• Neurogenic claudication

  • Pain or heaviness in both legs when walking or standing that improves with sitting or bending forward

  • Often a sign of spinal canal narrowing (stenosis), and the cyst can contribute to that narrowing

The MRI helps your doctor match what they see on the images to where you feel symptoms. If the cyst presses on the same nerve that corresponds to your pain pattern, it is more likely to be clinically important.

Is a Synovial Cyst Dangerous?

In most cases, a synovial cyst of the spine is not dangerous in the sense of being cancer or infection. It is instead a marker of underlying arthritis and degeneration.

Possible concerns:

• Persistent pain or nerve symptoms if the cyst presses on a nerve

• Worsening stenosis in people who already have a tight spinal canal

Radiologists usually make it clear that this is a benign, degenerative cyst. The MRI still matters because it helps guide treatment options if you have significant pain or neurologic symptoms.

Treatment Options and Role of Imaging

Treatment is based on how severe your symptoms are and how much the cyst is compressing nerves on imaging.

Common approaches:

• Conservative treatment

  • Pain medications, physical therapy, activity modification

  • Injections (facet joint injections, epidural steroid injections) to reduce inflammation and pain

  • This is often tried first if symptoms are mild or moderate.

• Image-guided procedures

  • In some centers, doctors may use CT or fluoroscopy guidance to try to aspirate (drain) the cyst or inject steroid into the joint.

  • Results can vary, and recurrence is possible.

• Surgical treatment

  • If symptoms are severe, persistent, or progressive, and MRI shows significant nerve compression, surgery may be recommended.

  • This can involve removing the cyst and sometimes decompressing the nerve by removing a small portion of bone or ligament.

  • In some cases, if there is instability, a fusion may be considered.

MRI is important both for planning treatment and for monitoring changes over time if needed. It gives a clear picture of the cyst size, location, and impact on nerves.

What Your MRI Report Might Say

Different radiologists use slightly different wording, but your report might include phrases like:

• “Facet joint synovial cyst at L4–L5 on the right.”

• “T2 hyperintense, T1 hypointense lesion adjacent to the right L4–L5 facet joint, compatible with a synovial cyst.”

• “Synovial cyst contributes to moderate right lateral recess stenosis and contacts the descending L5 nerve root.”

• “Findings are degenerative in nature.”

If you see these phrases, they are describing a benign cyst arising from an arthritic facet joint and explaining how it may be affecting the nearby nerves and spinal canal.

Key Takeaways

• A synovial cyst of the spine is a small, fluid-filled sac that comes from an arthritic facet joint.

• On MRI, it shows up next to a facet joint, often bright on fluid-sensitive images and sometimes compressing nearby nerves.

• It is non-cancerous and part of age-related spinal degeneration.

• Not all synovial cysts cause symptoms, but when they do, the MRI helps link the cyst to your back or leg pain.

• Treatment ranges from conservative care and injections to surgical removal, depending on how much the cyst is affecting your quality of life.

If you have questions about your MRI report, bring a copy to your appointment and ask your doctor to walk through the images and wording with you. Seeing the cyst on the images often makes the explanation much easier to understand.

References

https://radiopaedia.org/articles/spinal-synovial-cyst-1?lang=us

https://insightsimaging.springeropen.com/articles/10.1007/s13244-016-0463-z

https://www.mdpi.com/2077-0383/12/7/2664