Objective: The presentation of a patient with acute low back pain and distal radiation to the lower extremities is often attributed to a herniated nucleus pulposus (NHP). The purpose of this report is to illustrate how an intraspinal lumbar synovial cyst can have a similar presentation.
Case presentation: A 52-year-old man presented with low back pain with left lower extremity weakness and distal radiation. An electrodiagnostic evaluation was consistent with lumbar-sacral radiculopathy. Computed tomography and magnetic resonance imaging showed a synovial cyst of the L4-5 facet joint.
Intervention: The patient underwent a L4-L5 laminotomy, synovial cyst excision, and decompression of the L5 nerve root.
Results: There were no postoperative complications. The patient had residual left lower extremity numbness but gradually regained the strength of his left lower extremity. Intraspinal synovial cyst can mimic the clinical pattern of NHP.
Conclusion: An intraspinal lumbar synovial cyst can present with symptoms of nerve root compression. Given the presentation of lumbar-sacral radicular symptoms such as radiating pain, muscle weakness, and numbness, surgical excision of the lumbar synovial cyst remains the definitive treatment of choice.