There have been many reports about lumbar synovial cysts, discussing surgical or interventional treatment methods. However, there have been few reports about spontaneous regression of the cyst. We report a case of a lumbar synovial cyst that regressed spontaneously. To the best of our knowledge, this is the first report of a spontaneously regressed lumbar synovial cyst in Korea. The patient was a 59-year-old man who presented with a 6-month history of insidious pain onset in the lower back and right buttock. Upon MRI of the lumbar spine, grade 1 spondylolisthesis was revealed at the L4-5 level. An about 6mm-sized extradural cyst was detected at the medial side of the right L4-5 facet joint. His symptoms were disappeared upon facet block with 0.5% bupivacaine bilaterally at the L4-5 level. Six years later, he revisited our clinic due to low back pain and left leg radiating pain. Upon lumbar MRI, aggravated L4-5 spondylolisthesis with left-side disc protrusion was observed. However, we could not find the synovial cyst around the right L4-5 facet joint that had existed 6 years prior. The patient was treated conservatively because he refused surgery.
