Spontaneous resolution of symptomatic lumbar synovial cyst

Abstract

CLINICAL DETAILS

A 66-year-old male presented to our institution with 12 months history of severe back pain and left leg pain in L5/S1 distribution. On examination he had a normal neurology except for a dull left ankle jerk. Magnetic resonance imaging (MRI) of his lumbo-sacral spine showed a left L5/S1 synovial cyst (Fig. 1a and b). The findings and management options were discussed with the patient, who decided for a surgical option. However in view of his recent cardiac history it was decided to see him again in clinic in 6 months’ time. After reviewing him in clinic, he was added to the surgical waiting list and as his MRI scan was a year old, fresh set of scans was requested nearer to his operation date. Surprisingly his repeat MRI showed complete resolution of the L5/S1 synovial cyst (Fig. 2a and b).

Figure 1:

(a) Axial T2 weighted MRI showing a left sided L5/S1 synovial cyst impinging on the left S1 nerve root; (b) sagittal T2 weighted MRI showing a L5/S1 synovial cyst.

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Figure 2:

(a) Axial T2 weighted MRI showing complete resolution of the synovial cyst; (b) sagittal T2 weighted MRI showing complete resolution of the synovial cyst.

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DISCUSSION

Synovial cyst is a cyst with clear or xanthochromic fluid within a synovium lined cavity which communicates with a joint capsule [1]. In the lumbar spine, synovial cyst arises from the medial margin of the facet joint and can cause lateral recess or central canal stenosis leading to radiculopathy, neurogenic claudication, sensory or motor deficits, reflex abnormalities and back pain [2]. At times it may be asymptomatic and discovered incidentally.

Synovial cysts are most common in the sixth decade of life as seen in our patient. Though our patient was a male, synovial cyst may have a slight female preponderance and most common spinal level affected is L4–L5 followed by L5–S1, L3–L4 and L2–L3 [3]. Incidence of lumbar synovial cyst (LSC) ranges between 0.8% and 2.0% on imaging [4] whereas it is between 0.01% and 0.8% [4] among patients undergoing lumbar spinal surgery. However, the exact etiopathogenesis of these synovial cysts is unclear but factors such as facet joint arthropathy, spinal instability and degenerative spondylolisthesis causing micro-trauma have been implicated [3].

MRI is the modality of choice for diagnosing synovial cysts as sensitivity of computer tomography (CT) is only 60% as compared to 90–95% for MRI [5, 6]. MRI appearance depends upon the composition of the cystic fluid. MRI typically shows a well-defined extra-dural mass with iso-intense fluid signal on T1 and hyper-intense fluid signal on T2 [1]. Hyper-intensity on T1 may indicate the presence of high protein content or hemorrhage whereas hypo-intensity on both T1 and T2 sequences indicate the presence of calcification.

Management of symptomatic LSC is controversial as natural history of the disease is unknown. Treatment options are conservative and surgical. Conservative management includes bed rest, analgesia, bracing, CT guided percutaneous cyst aspiration and facet joint and epidural steroid injection. A number of authors have published results of conservative management with varying degree of success (Table 1). Surgery is indicated in patients with progressive neurological deficit or intractable pain not responding to conservative treatment. However, there is also controversy regarding ideal surgical management. Some surgeons recommend cyst excision with decompression as a primary procedure whereas others tend to combine it with spinal fusion as degenerative spondylolisthesis can be present in a number of patients with LSC (38.0–75.0%) [6] (Table 2). Though there is no consensus regarding management of degenerative spondylolisthesis associated with LSC. Some authors [7] advocate fusion as a primary procedure in the presence of instability or when facetectomy is performed for the management of LSC whereas others [8] recommend pre- and post-operative dynamic studies to assess suitability for fusion either as a primary or secondary procedure.

The failure rate with conservative treatment is around 47% [6]. Some authors argue that since about 50% of the patients benefit from conservative treatment, a trial of cyst aspiration +/– steroid injection may be considered before opting for more invasive surgical procedure which is associated with higher incidence of post-operative complications. The success rate with surgery is 72–100% [6] but there is no consensus about procedure even if no fusion is being performed. Literature review reveals that authors have tried hemilaminectomy, laminectomy or facetectomy either alone or in combination for treatment of symptomatic LSC. Some others have also attempted minimally invasive resection of LSC with encouraging results (Table 3).

Spontaneous regression of symptomatic LSC is uncommon and has only been reported on a handful of occasions (Table 4). Factors which may contribute to spontaneous disappearance are extrusion of contents of the cyst and resorption of cyst wall or changes in local forces which initially led to synovial cyst formation [9, 10]. Synovial cysts show a female preponderance, so it is not surprising that most cases of spontaneous regression of symptomatic LSC have been reported in female patients. Our case of spontaneous regression of symptomatic LSC adds to the growing list of such cases and may help in understanding the natural history of the disease process in future. Also as there is controversy regarding optimal management of symptomatic LSC and few reports of spontaneous regression, there may be an argument for managing some patients conservatively with wait and watch approach.

Management of symptomatic LSC should be on a case to case basis depending upon presenting signs and symptoms, radiological findings, surgeon's expertise and patient's aspirations. Most studies show that surgery is superior to conservative management, however, as far as answer to the important question of ‘to fuse or not to fuse’ – the jury is still out. A randomized control trial may be needed to decide the optimal treatment for symptomatic LSC.

CONFLICT OF INTEREST STATEMENT

None declared.

REFERENCES