SCs are herniations of the synovial membrane through the capsule of a joint filled by synovial fluid, which may or may not keep a communication with the joint.
The MRI features consists of rounded cystic lesions arising from the medial aspect of degenerated facet joints filled with synovial fluid, usually smaller than 20 mm. They tend to course with lateral recess stenosis and present dense adhesions to dura and nerve roots.
The great majority of SCs arising from facet joints occur in the lumbar spine, L4/L5 being the most affected level. These lesions are seldom reported in the cervical spine and are even rarer in the thoracic spine.
They are thought to serve as drainage reservoirs for the excessive joint effusion in the setting of any arthropathy, escaping from its regular location through a one-way-valve mechanism into the area of least resistance.
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