Symptoms of Synovial Cysts in the Spine
Many patients only find out that they have synovial cysts when undergoing X-Rays or MRI scans for other conditions and these asymptomatic patients rarely require back surgery or other treatment for cysts in the spine. Where the size or location of a synovial spinal cyst creates pressure on the spinal nerves or cord it is more likely that patients will suffer from symptoms of synovial cysts such as back pain, tenderness, numbness, weakness, and even radiculopathy down the arms or, more commonly, the legs. Lumbar synovial cysts occurring at L4/5 are the most common type, followed by cysts at L5/S1, and so lumbar spinal stenosis and resulting lower back pain are the most common symptoms of spinal cysts.
Who Gets Spinal Cysts?
The development of intraspinal synovial cysts is thought to be a result of osteoarthritis in most patients and so it may be that patients develop other symptoms of this condition that are not directly related to the spinal cyst. Due to spinal cysts being connected to degeneration of the spine it is unusual to see the condition in patients under forty-five and is much more common in those over sixty-five years of age. Osteophyte growth can occur in cases of degenerative spinal arthritis and these bone spurs may themselves be responsible for spinal stenosis, pinched nerves, and/or spinal cord impingement. Back surgery to remove the osteophytes and stabilize the spine are more likely to effectively reduce or resolve symptoms in such cases rather than simply aspirating the synovial cyst to have it return at a later date. Most cysts develop due to osteoarthritis of the facet joints and are frequently connected to spondylolisthesis and, occasionally, scoliosis. Other factors in cyst formation include increased production of hyaluronic acid by fibroblasts and non-specific proliferation of mesenchymal cells.
What Causes Spinal Cysts?
Synovial cysts usually arise from the medical margin of the facet joint, pushing into the space in the central spinal canal through the lateral recess. In some cases, patients may have synovial sac protrusion into the dorsal central spinal canal as the synovial fluid pushes the sac beneath the ligamentum flavum in the midline. The location of the protruding synovial fluid-filled sac will affect the approach taken during back surgery as a flavectomy to decompress the spine is likely to be of more benefit in the latter case, whereas a facetectomy could be favored in the former scenario. Patients usually present with radicular pain after chronic lower back pain, although some patients also report neurogenic claudication and symptoms of spinal cord compression, such as cauda equina, from synovial cysts in the back.
Diagnosing Cysts in the Spine
Diagnosing intraspinal synovial cysts will usually involve imaging of the lumbar spine, the most common site of such cysts, using MRI or X-Ray techniques. Cysts in the cervical and thoracic portions of the spine also occur but the sacral spinal region is not thought to develop intraspinal cysts. On magnetic resonance imaging (MRI) these intraspinal cysts show up as well defined, smooth masses outside the dura (the spinal cord’s protective film) and are usually next to a facet joint which also shows signs of degeneration. Serous fluid typically presents as a low-intensity T1 signal and a hyperintense T2-weighted image allowing radiologists the opportunity to identify the type of fluid filling the cyst.