Working Diagnosis:
Large right-sided L4-L5 synovial cyst causing lumbosacral radiculopathy

Treatment:
She was referred to Physical Medicine and Rehabilitation for possible cyst aspiration/rupture. At the time of the Physical Medicine and Rehabilitation visit three weeks later, she reported development of bowel and bladder incontinence consistent with cauda equina syndrome and therefore was urgently referred to Neurosurgery. She underwent a successful L4-L5 laminectomy with facet cyst excision and L4-L5 interbody fusion.

Outcome:
By two months post-operatively, she had full resolution of bowel and bladder incontinence. She continued to have right leg neuralgia requiring management with Lyrica which was resolved six months post-operatively. By six months post-op, she had returned to cycling and was working with physical therapy to initiate running.

Author's Comments:
Low back pain with radiculopathy is most often caused by disc herniation. Synovial facet cysts are less prevalent and many remain asymptomatic, though over half cause radicular symptoms. MRI is the imaging tool of choice for diagnosis. Conservative management includes nonsteroidal anti-inflammatory agents, physical therapy, epidural steroid injections, and cyst aspiration or rupture. However, synovial facet cysts have a high recurrence rate after these interventions. Surgical decompression is recommended for patients with significant neurologic symptoms or who do not improve with conservative management. It is rare for synovial facet cysts to cause cauda equina syndrome, however, this can occur and is an indication for urgent surgical referral as demonstrated in this case report.

Editor's Comments:
Patients with symptomatic synovial cysts typically present with unilateral or bilateral radicular pain. Lumbar synovial cysts come from dilatations of the synovial sheath arising from the facet joints which extrude into the spinal canal and can contain either gelatinous or serosanguinous material. Aspiration is often not helpful as the remaining fibrous capsule continues to contribute to compression of associated neural elements. Although cauda equina is rare with synovial cysts, all patients should be counseled on to seek emergency care for progressive neurologic symptoms.

References:
Casey, E. Natural history of radiculopathy. Physical Medicine and Rehabilitation Clinics of North America. 2011;22(1):1-5
Janseen SJ, Ogink PT, Schwab JH. The prevalence of Incidental and Symptomatic Lumbar Synovial Facet Cysts. Clinical Spinal Surgery. 2018;31(5):E296-301
Epstein NE, Baisden J. The diagnosis and management of synovial cysts: Efficacy of surgery versus cyst aspiration. Surgical Neurology International. 2012;3(Supl3):S157-166
Boody BS and Savage JW. Evaluation and treatment of lumbar facet cysts. Journal of the American Academy of Orthopaedic Surgeons. 2016;24(12):829-842
Shaw M, Birch N. Facet joint cysts causing cauda equina compression. Journal of Spinal Disorders and Techniques. 2004;17(5):442-445
Sinha P et al. Spontaneous resolution of symptomatic lumbar synovial cyst. Journal of Surgical Case Reports. 2016;(10):rjw166

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