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Diagnosis: Synovial cyst right L4-5 Intraspinal synovial cysts are fairly uncommon and are associated with degenerative spondylosis of the spine. The most common location for synovial cyst is in the lower lumbar spine. They are typically adjacent to the facet which will usually demonstrate some degree of degenerative change. They may project outward and simulate a herniated disk. One helpful feature to help differentiate a synovial cyst from a herniated disk is the fact the synovial cyst will usually show some degree of continuity with the facet joint and the adjacent ligamentum flavum. Patients are usually over age 50 and may complain of radicular symptoms. The imaging characteristics are variable. They may have calcification on CT or they may contain air, fluid or hemorrhagic breakdown products. There is a report of sudden hemorrhage into a synovial cyst resulting in acute cauda equina syndrome. Enhancement characteristics of synovial cysts are variable. There may be solid or peripheral enhancement of the lesion or enhancement of the facet joint.
In general, the differential of a synovial cyst includes extruded disk fragment and nerve root schwannoma. For extruded disk fragment look for an abnormal disk space at that level or at neighboring levels in case the fragment had migrated. In this case, the presence of fluid within the adjacent facet joint and the fact that the lesion is contiguous with the facet joint strongly suggests synovial cyst. The patient underwent a right partial hemilaminectomy and medial facetectomy at the L4-5 level with foramenotomy over the right fifth lumbar nerve root. After elevation of the ligamentum flavum a synovial cyst measuring about 2 cm in diameter was seen indenting the dural sac and was removed.