Original Article

Intraspinal lumbar synovial cysts: Diagnosis and surgical management

R. Indar, E. Tsiridis, M. Morgan, C.H. Aldham, A.A. Hussein
Department of Trauma and Orthopaedics, Princess Alexandra Hospital, Harlow, Essex, CM20 1QX, UK

Correspondence to: R Indar, 67C Granville Park, Lewisham, London, SE13 7DW Email: rupertindar@hotmail.com

Introduction Materials and methods Results

Discussion Conclusion References

Keywords: Synovial cysts, facet joints, osteoarthritis, radicular pain, surgical decompression
Surg J R Coll Surg Edinb Irel., 2 June 2004, 141-144

Background: Lumbar synovial cysts are a common association of facet joint degenerative disease. However, it is a relatively rare for these cysts to cause symptoms of radiculopathy and nerve root compression. Patients and Methods: We report a series of eight cases which were treated over a period of 20 months. There were five female and three male patients with a mean age of 66 years, and an average follow-up of seventeen months. All patients had pre-operative flexion/ extension radiographs and MRI scans. Two patients had failed non-surgical treatment, two were associated with a Grade 1 spondylolisthesis, and all were associated with facet joint arthropathy. There were five cases occurring at L4/5 and three at L5/S1. Results: All patients underwent identical procedures, which involved exploration, hemi-laminotomy, flavectomy and minimal facet joint excision. No patient required posterior lumbar interbody fusion and at follow-up five patients had excellent and three had good results

INTRODUCTION
In 1877, Baker originally described synovial cysts as being secondary to processes occurring within an adjacent degenerated joint as later described in the knee joint.¹ Soon after, Von Gruker reported the finding of an extra-dural, intraspinal synovial cyst of the spine at autopsy. These intraspinal, extradural cystic lesions develop as a consequence of osteoarthritis of facet joints and most commonly occur at the L4/5 level and to a lesser extent the L5/S1 level. They usually arise from the medial margin of the facet joints, projecting into the lateral recess of the central spinal canal, but can also dissect beneath the ligamentum flavum in the midline into the dorsal central spinal canal or anteriorly, causing nerve root compression. The most common presentation is radicular pain preceded by chronic lower back pain, and less common symptoms are neurogenic claudication or spinal cord compression.^2-4

MATERIALS AND METHODS
Eight cases of intraspinal cysts were evaluated and treated surgically over a 20-month period. All the clinical features and duration of symptoms, age and sex were analysed (see Table). There were five female and three male cases with a mean age of 66 years (range 54-79), and an average follow-up of 23.7 months. All patients had pre-operative magnetic resonance imaging (MRI) and lateral flexion/extension radiographs all underwent identical procedures which involved exploration, hemi-laminotomy, flavectomy and piecemeal excision of cysts, followed by bed rest, and mobilisation with a physiotherapy regime. Two of the eight cases failed conservative treatment, of which one had a corticosteroid injection and the other had facet joint aspiration after a facetogram.

The outcome was graded as excellent, good or poor based on the resolution of symptoms, reversal of neurological deficit and whether the patient was able to return to an activity level equal to that before the onset of disease. Patients who had no discomfort of back/leg and returned to full activities within eight weeks post-operative were deemed excellent, those who had complete resolution of neurological symptoms and signs with minimal back/leg pain were graded as good, and those cases with frequent back/leg pain and limited activity were graded as a poor outcome.

RESULTS
All patients in this series had a single, unilateral intraspinal cyst associated with facet joint degenerative disease as proven on magnetic resonance imaging (MRI). There were five and three cases occurring at the L4/5 and L5/S1 levels, respectively, with two of the latter associated with a Grade 1 degenerative spondylolisthesis (see Table 1).

Five cases had excellent and three cases had a good outcome. The three cases that had a good outcome had preoperative clinical and radiological evidence of degenerative disc disease, and had mild lower back pain but returned to full activities. None of the cases required fusion at the time of surgery (average 23.7 months, 12-33 months), and there was no radiological evidence of instability at follow-up.

DISCUSSION
The term ‘Juxta-facet cyst’ is applied to both synovial and ganglion cysts as described by Kao et al. (1974), although the distinction between the two is of pathological interest 
only.^{2, 3}

Most cysts develop as a consequence of osteoarthritis of facet joints and are commonly associated with spondylolisthesis and less commonly with scoliosis. These include myxoid degeneration with cyst formation, increased hyaluronic acid production by fibroblasts and non-specific proliferation of mesenchymal cells.

Although juxta-facet cysts occur mostly in the middle-aged and elderly, and show a predilection for the lower lumbar spine, they have been reported in all areas of the spine except the sacrum. There are reports in the literature of juxta-facet cysts occurring in the cervical and thoracic spine.^5,6

Most patients presented with radicular pain which may or may not be preceeded by lower back pain (see Table 1). In addition, patients may suffer from neurogenic claudication if 

the cyst significantly compromises the spinal canal. Several authors have reported cases of haemorrhage into synovial cysts such that symptoms are exacerbated due to increased nerve root compression, and this may even lead to cauda equina syndrome.⁷

The pre-operative diagnosis can be made by MRI. On MRI, these cysts appear as well circumscribed, smooth, extradural masses located adjacent to the facet joint that more often than not displays changes with degenerative disease, whose imaging signal is variable depending on the type of fluid within the cyst. Typically when there is serous fluid, there is a low-intensity T1 signal and a hyperintense T2-weighted image (see Figures 1-3).

Figure 1: Axial T1+T2 weighted images. Axial scans show a large right-sided cyst, originating from the facet joint and causing narrowing of the exiting foramina.

Figure 2: Saggital T1+T2 weighted images. T1 image shows a cyst with low intensity signal, and hyperintense on the T2-weighted weighted image.

Figure 3: Coronal T1-weighted image. Well defined large cyst (low intensity) causing compression of the dural sac.

Some authors believe that the symptoms caused by cysts do not represent nerve root compression but reflect underlying facet joint degenerative changes and, therefore, surgery is not indicated and conservative treatment of injection with corticosteroids/repeated aspiration should be implemented. Bjorkengren et al. (1987) and Mariette et al. (1984) have both published small series of patients with intra-spinal cysts treated with such injections showing satisfactory results.^8,9 Other series have shown conservative treatment to be ineffective in the medium and long-term.¹⁰

Surgical decompression can be difficult in some cases, because the cyst may be adherent to the dura. However, the extent of decompressive surgery should depend not only on the size of the cyst but also on the extent of interface with the dura. Following exploration, flavectomy and laminotomy the nerve roots and the dural sac should be decompressed, the cyst totally excised and, if required, a medial facetectomy performed. In the latter procedure, great care was taken not to destabilise the segment involved.

CONCLUSION
We have described a relatively small series of intraspinal lumbar synovial cysts, describing their presentation, pathogenesis, treatment and outcome. It is important to differentiate these cysts from the more common causes of nerve root compression such as a herniated nucleosus pulposus and other causes - neurofibroma, haematoma, abscess and metastatic disease. We have shown that with careful assessment, these intraspinal cysts can be accurately diagnosed and treated by surgical intervention successfully, without the need for a spinal fusion.

REFERENCES
1. Baker WM. Formation of abnormal synovial cysts in the leg in connection with the joints. St. Bartholomews Hospital Reports 1885;21: 177-190.
2. Kao CC, Winkler SS, Turner JH. Synovial cyst of spinal facet: case report. Journal of Neurosurgery 1974; 41: 372-376.
3. Rosenberg AE, Schiller AL. Tumours and tumour-like lesions of joints and related structures, in Kelley W. Textbook of Rheumatology ed 5 1997; Vol 2: 1593-1595.
4. Chimento GF, Ricciardi JE, Whitecloud TS111. Intraspinal extradural ganglion cyst. Journal of Spinal Disorders 1995; 8 :82-85.
5. Lunardi P, Acqui M, Ricci G, Agrillo A, Ferrante L. Cervical synovial cysts: case report and review of the literature. Eur Spine Journal 1999; 8: 232-237.
6. Doherty PF, Sherman BA, Stein SC, White R. Bilateral synovial cysts of the thoracic spine: a case report. Surg Neurol 1993; 39: 279-281.
7. Tatter S, Cosgrove GR. Haemorrhage into a lumbar synovial cyst causing acute cauda equina Syndrome: Case report. Journal of Neurosurgery 1994; 81: 449-452.
8. Bjorkengren AG, Kurz LT, Resnick D, et al. Symptomatic intraspinal synovial cysts: opacification and treatment by percutaneous injection. American Journal of Radiology 1987; 149: 105-107.
9. Mariette X, Glon Y, Clerc D, et al. Medical treatment of synovial cysts of the juxtapophyseal joints: four cases with long-term follow-up. Arthritis Rheum 1989; 32: 660-661.
10. Liu SS, Williams KD, Drayer BP, et al. Synovial cysts of the lumbrosacral spine: diagnosis by MR imaging. American Journal of Neuroradiology 1989; 10: 1239-1242.

Copyright: 16 March 2004