Lumbar synovial cyst as a cause of low back pain and acute radiculopathy: a case report.

Abstract: The authors report the case of a 69-year old female with a persistent history of low back pain. Plain lumbar radiographs, performed at symptom initiation, revealed lumbar spondylolisthesis. Low back pain was attributed to this, and the patient received conservative treatment with partial relief of symptoms. Four years later, and as a result of acute onset of radicular symptoms, a lumbar spine magnetic resonance imaging scan was performed, revealing an epidural cystic lesion. The cyst was removed, and histopathology revealed a synovial cyst.

Key Words: epidural space, low back pain, lumbar spine, synovial cyst

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Synovial cysts most commonly involve the joints of extremities, and are rarely found in the spinal canal. The frequency of diagnosis may be on the rise, however, because of the aging population and high diagnostic yield of magnetic resonance imaging (MRI) scans. Because of their rarity, synovial cysts are easily misdiagnosed in cases of persistent low back pain (LBP) and radiculopathy, and are often attributed to herniated nucleus pulposus or spondylosis. When synovial cysts are manifested as such, they can pose serious diagnostic problems, lead to delayed treatment, and result in a worse prognosis for neurologic outcome.

Case Report

A 69-year-old female with a 4-year history of LBP was admitted to our department due to sudden onset of radicular pain in the left leg. Pain was persistent despite conservative treatment with analgesics. She was initially examined by a general practitioner who prescribed plain lumbar spine radiography, which revealed lumbar spondylolisthesis. She was treated with analgesics and physiotherapy, which offered partial relief. However, pain had gradually worsened during the 6 months leading up to her most recent admission.

On neurologic examination, she had 4/5 muscle strength in the plantar flexor muscle on the left, and the ankle jerk was absent. Pain was accompanied by numbness and reduced sensation on the dorsal surface of her left foot. There was a positive straight leg-raising test at 25 degrees on the left. Plain radiographs showed no pathologic findings. A lumbar computed tomographic (CT) scan showed a low-density cystic mass posterolateral to the left lumbar (L) 5 nerve root, adjacent to the facet (Fig. 1). An MRI revealed a well-defined extradural cystic mass, compressing the left L5 root (Figs. 2 and 3).

Four days later, a L4 hemilaminectomy to the left was performed. The cyst was located in continuity with the L4/5 facet joint and was totally removed. Histopathologic examination revealed a 1.9-cm cyst of fibrous connective tissue covered with synovial lining, with regions of focal inflammation. After surgery, the patient had complete symptom relief.

Discussion

Synovial and ganglion cysts are generally described under the term juxta-facet cysts, first introduced in 1974 by Kao et al. (1) Synovial cysts result from the protrusion of synovial lining through a defect or rupture of degenerated facet joints. Theories on the underlying cause include trauma, facet joint degeneration, spondylosis, and spondylolisthesis. Most juxta-facet cysts are observed at the L4/5 level, which has the most motion within the lumbar spine.

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Symptoms and signs are usually nonspecific in nature and mimic more commonly encountered spinal diseases such as spondylosis, herniated disc, or spinal stenosis. Furthermore, as the cyst expands locally, it may compress parasympathetic fibers to the bladder, bowel, or sexual organs, or selectively compromise a single dorsal root. Thus diagnoses of "cystocele," "prostatic hypertrophy," and "atypical sciatica" are also frequently made. (2) Other features include nocturnal pain and pain with recumbency, believed to be mediated through the stretching of spinal roots over the cyst. Symptoms may fluctuate because these cysts change in size and may increase under mechanical stress. Because of the mobility of roots and the wide intradural space, lumbar synovial cysts often reach a considerable size before causing symptoms, and therefore have a worse prognosis for neurologic outcome. In the case reported herein, symptoms of LBP persisted for over a period of 4 years before treatment. An initial diagnosis of spondylolisthesis by plain radiography along with partial symptom relief by analgesics led to delayed investigation by advanced neuroimaging.

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Lumbar spine imaging studies should be used to confirm findings gathered from a thorough history and physical examination. Plain radiographs are usually the first imaging modality to be used in the differential diagnosis. The lower spine, though, is a difficult location for early radiographic recognition of cystic lesions, and plain radiographs can be misleading. This is due to the late occurrence of osseous changes secondary to such lesions, the inability to image soft tissues, and the superimposition of other bone and soft tissue shadows. CT scan is of greater utility, and usually reveals a low-density epidural cystic lesion with a posterolateral juxta-articular location. Other features may include a hyperintense rim caused by calcification, and hypointense ingredients attributable to gas. (3)

MRI is the imaging modality of choice because of its high sensitivity. MRI allows visualization of the cyst in all anatomic planes, and enables assessment of typical accompanying changes such as degenerative spondylolisthesis and facet hypertrophy. Synovial cysts may generate a variety of MRI signals depending on their often variable content (which may include recurrent hemorrhage or gas (4)), or according to the degree of the cyst wall's calcification. In T1-weighted images, the signal intensity is equal or slightly greater than that of cerebrospinal fluid, as a result of the higher protein content of the fluid within the cyst. (5) Irregular and inhomogeneous hyperintensity may indicate subacute or recurrent hemorrhage. In T2-weighted images, synovial cysts show a hyperintense center and hypointense rim.

Treatment may be either conservative or surgical. Conservative treatment is preferred if the cyst wall is not calcified and symptoms show gradual decrease. There have been reports of cysts spontaneously resolving, presumably because of wall collapse or inflammation resolution. (6) Injection of corticosteroids epidurally or into the corresponding facet joint may reduce the inflammatory process and resolve symptoms in up to 70% of patients, but is only temporarily effective. (7) In cases of intractable pain and significant clinical symptomatology that persists despite conservative methods, surgical excision remains a safe and definitive treatment. (7) The surgical approach requires a wide exposure to provide access to the lesion and the adjacent neural structures, and to enable careful dissection while protecting important structures.

Conclusion

Lumbar synovial cysts are a more common cause of LBP and lumbar radicular pain than previously thought. Physicians should be aware of this entity and keep it in mind in the differential diagnosis of patients with persistent LBP. A detailed history and careful physical examination can help identify candidates that require early screening tests and specialty referral. Clearly, patients who present with focal neurologic deficits, a confusing clinical presentation, nocturnal pain or pain with recumbency, and whose symptoms progress or fail to respond to conservative treatment should undergo further investigation with advanced neuroimaging studies. Early recognition and treatment helps prevent complications and leads to improved outcome, whereas preoperative diagnosis allows more precise surgical planning, thus diminishing the risks inherent to surgery.

Men have become the tools of their tools.
--Henry Daivd Thoreau

Accepted February 6, 2004.

References

1. Kao CC, Winkler SS, Turner JH. Synovial cyst of spinal facet: case report. J Neurosurg 1974;41:372-376.

2. Tolias CM, Beale DJ, Sakas DE. Giant lumbar meningioma: a common tumour in an unusual location. Neuroradiology 1997;39:276-277.

3. Schulz EE, West WL. Hinshaw DB, et al. Gas in a lumbar extradural juxta-articular cyst: signs of synovial origin. Am J Radiol 1984;143:875-876.

4. Eyster EF, Scott WR. Lumbar synovial cysts: report of eleven cases. Neurosurgery 1989;24:112-115.

5. Tillich M, Trummer M, Lindbichler F, et al. Symptomatic intraspinal synovial cysts of the lumbar spine: correlation of MR and surgical findings. Neuroradiology 2001;43:1070-1075.

6. Jackson DE Jr, Atlas SW, Mani Jr. Intraspinal synovial cysts: MR imaging. Radiology 1989;170:527-530.

7. Hagen T, Daschner H, Lensch T. Juxta-facet cysts: magnetic resonance tomography diagnosis. Radiologe 2001;41:1056-1062.

RELATED ARTICLE: Key Points

* Synovial cysts may be a more common cause of low back pain and acute radiculopathy than previously thought.

* Symptoms and signs associated with synovial cysts are usually nonspecific and mimic more commonly encountered spinal diseases.

* A detailed history and clinical examination is essential in selecting patients who should undergo early advanced neuroimaging studies.

* Early diagnosis and treatment help prevent neurologic sequelae.

Andreas T. Kouyialis, MD, Efstathios J. Boviatsis, MD, Stefanos Korfias, MD, and Damianos E. Sakas, MD

From the Department of Neurosurgery, Evangelismos General Hospital, University of Athens Medical School, Athens, Greece.

Reprints requests to Dr. Efstathios J. Boviatsis, Department of Neurosurgery, Evangelismos General Hospital, 61 Ipsilantou St, Athens 115 21, Greece. Email: [e-mail]