A spinal synovial cyst is a benign, fluid-filled sac that develops in a spinal joint, most often in the lumbar, or lower, region of the back. These cysts are a consequence of the natural aging process that affects the spine’s joints. While they are not cancerous, they can press on adjacent nerves, leading to noticeable symptoms.
What is a Spinal Synovial Cyst?
Spinal synovial cysts originate from the facet joints, which are small, stabilizing joints at the back of the spine. These joints are lined with a membrane called the synovium that produces lubricating fluid. Due to age-related wear and tear from conditions like osteoarthritis, the cartilage in these joints can break down.
This degenerative process can cause the body to produce an excess amount of synovial fluid. If small tears form in the joint capsule, this extra fluid can escape and accumulate into a contained, fluid-filled sac known as a synovial cyst. The cyst can gradually grow in size as more fluid collects within it, potentially encroaching on the spinal canal.
Common Symptoms
Symptoms arise not from the cyst itself, but from the pressure it exerts on the spinal cord or nearby nerve roots. Many small cysts remain asymptomatic. When a cyst becomes large enough to cause compression, it can lead to pain in the lower back. This discomfort often increases with activities like walking or standing and may be relieved by sitting down.
A frequent symptom is radiculopathy, where pressure on a specific nerve root causes pain, numbness, or weakness that travels down that nerve’s path. When this affects the sciatic nerve, it results in pain radiating down the back of the leg. Another symptom is neurogenic claudication, characterized by cramping, pain, or a heavy sensation in the legs that occurs with walking or prolonged standing.
Diagnosis and Imaging Examples
The most definitive method for diagnosing a spinal synovial cyst is a Magnetic Resonance Imaging (MRI) scan. Because an MRI excels at visualizing soft tissues, it allows doctors to clearly see the fluid-filled sac, the spinal nerves, and the extent of any compression.
In an axial MRI view of the lumbar spine, a synovial cyst appears as a well-defined, bright, round structure adjacent to a facet joint. This brightness on a T2-weighted image is characteristic of fluid. The cyst can be seen encroaching upon the spinal canal, the space normally occupied by nerves. As the image below shows, the cyst can visibly compress the nerve roots.
This visual evidence is important for confirming the diagnosis and planning treatment. The image allows a physician to assess the severity of the nerve compression and correlate it with the patient’s reported symptoms.
Treatment Approaches
The approach to treatment depends on the severity of the symptoms. For individuals with mild or no symptoms, a period of observation may be all that is needed, as some cysts do not worsen over time. Non-surgical management includes physical therapy to strengthen supporting muscles and improve spinal stability, along with activity modification to avoid positions that exacerbate pain.
For more significant pain, a physician may recommend a corticosteroid injection. This involves injecting anti-inflammatory medication into or near the cyst under imaging guidance to reduce swelling and relieve nerve pressure. If conservative measures fail to provide lasting relief or if significant weakness is present, surgery may be considered. The standard surgical procedure is a decompression, which involves removing the cyst to free the compressed nerves.