Intraspinal Synovial Cyst of Facet Joint with Vacuum: a case report

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Chin J Radiol 2004; 29: Intraspinal Synovial Cyst of Facet Joint with Vacuum: a case report MEI-CHUN CHOU 1 LEE-REN YEH 1,2 CLEMENT KH CHEN 1,2 HUAY-BAN PAN 1,2 Department of Radiology 1, Kaohsiung
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Chin J Radiol 2004; 29: Intraspinal Synovial Cyst of Facet Joint with Vacuum: a case report MEI-CHUN CHOU 1 LEE-REN YEH 1,2 CLEMENT KH CHEN 1,2 HUAY-BAN PAN 1,2 Department of Radiology 1, Kaohsiung Veterans General Hospital School of Medicine 2, National Yang-Ming University Typical synovial cyst arising from degenerative facet joint usually appears isointense to slightly hyperintense to cerebrospinal fluid on T1-weighted and hyperintense on T2-weighted conventional magnetic resonance (MR) imaging. We present a case of intraspinal synovial cyst with thecal sac compression that manifesting low signal intensity on both T1- weighted and T2-weighted MR imaging due to the gas-containing nature. It may be difficult to be differentiated from crystal deposition or giant osteophyte formation if no other modality such as computed tomography is available for correlation. The entity of synovial cyst with vacuum should be included in the differential diagnoses when evaluating a patient with posterolateral epidural lesion that is hypointense at all MR pulse sequences. Key words: Spine, facet joints; Synovial membrance, cysts Reprint requests to: Clement KH Chen Department of Radiology, Kaohsiung Veterans General Hospital. No. 386, Ta Chung First Road, Kaohsiung 813, Taiwan, R.O.C. Synovial cysts of the lumbar facet joints have been increasingly reported in recent years since the magnetic resonance technique was available [1-4]. The synovial cysts are usually associated with osteoarthritis of the facet joint, or post-traumatic changes, either in the presence or absence of spondylolisthesis. Surgical resection is usually necessary if patients suffer from radiculopathy or neurologic symptoms. Synovial cysts with vacuum have been mentioned in the literature [9] but only few reports regarding to its imaging features were available. Here we present a case of synovial cyst with vacuum of the facet joint, which may be challenging to the diagnosis if only conventional magnetic resonance (MR) imaging was performed. CASE REPORT A 72-year-old male visited our orthopedic department because of chronic low back pain with radiation to the lower legs and recent onset of bilateral lower legs weakness. Physical examination was not unusual except mildly decreased muscle power of the left lower leg. The patient was otherwise healthy and without history of systemic disease, alcoholism, or malignancy. The family history was also noncontributory. The routine blood tests were within normal ranges. The radiographs of lumbar spine disclosed mild rotatory scoliosis and degenerative change of lumbar spine with hypertrophic change of the facet joint. The MR imaging was performed (1.5-T system; Signa; General Electric Medical Systems, Milwaukee, WI) and revealed an intraspinal lesion adjacent to the left L4- L5 facet joint with narrowing of the lateral recess and compression of the thecal sac. The lesion was hypointense on axial spin echo (SE) T1-weighted (repetition time/echo time = 666/18), axial fat-suppressed fast spin echo (FSE) T2-weighted (4000/80), and sagittal T2-weighted (4137/80) sequences (Fig. 1). Crystal deposition of ligamentum flavum and facet capsule, or giant osteophyte from facet joint were considered initially based on its location and signal char- 158 Intraspinal synovial cyst of facet joint with vacuum 1a 1c 1b Figure 1. Axial SE T1-weighted (TR/ TE 666/18) image a. axial fat-suppressed FSE T2-weighted (4000/80) image b. at the level of L4-5 and the sagittal T2-weighted (4137/80) image c. showed a hypointense intraspinal juxta-articular lesion (arrow), closely attached to the left facet joint, with compression of the lateral recess and the thecal sac. acteristics. Due to the non-conclusive findings based on MR images, non-contrast computed tomography (CT) scan (Somatom HQ; Siemens, Erlangen, Germany) was then undertaken. It disclosed the gascontaining nature of the lesion (Fig. 2) and was straightforward to the final diagnosis of intraspinal juxta-articular synovial cyst with vaccum. The wall of the cyst showed high attenuation on CT study, suggesting possibility of calcification of the cyst wall. The patient was under conservative medical treatment with gradually subsided symptoms. The patient kept followed-up at the out-patient department and was doing well for years. DISCUSSION The actual etiology of intraspinal synovial cysts is still not well-understood, but has been considered to associate with the degenerative osteoarthritis of the facet joints [2,6] and the spondylolisthesis [4,6]. It is Figure 2. Axial CT image at the same location as figure 1a and 1b disclosed the gas-containing nature of the synovial cyst (arrow) of left facet joint. A calcified rim was also noted. Intraspinal synovial cyst of facet joint with vacuum 159 generally accepted that the synovial cysts probably originate from synovium herniating through a weakened facet joint capsule. Other pathogenesis have also been proposed, including myxoid degeneration of periarticular fibrous tissue, increased secretion by fibroblasts following trauma, growth of developmental synovial rests, and proliferation of pluripotential mesenchymal cells [7, 8]. On the MR images, a synovial cyst typically presents as an intraspinal extradural well-circumscribed cystic mass arising from the adjacent facet joint. It usually appear isointense to slightly hyperintense to cerebrospinal fluid on short TR/TE images and hyperintense on long TR/TE sequences, due to the high content of the proteinacious fluid. A thickened hypointense rim on long TR/TE images has been observed in some of the lesions, probably reflects fine calcification or hemorrhage in the margins of the cysts [2, 8]. Gas-filled synovial cysts have been reported and be postulated the possibility of an adjacent diseased facet joint with a vacuum cleft, which consequently W.eW.hg W.YW.Yhg 7U7Uhg S5eS5hg W.YW.Yhg dissected into the cyst [9]. The vacuum phenomenon was first reported in 1937 by Magnusson who described as accumulation of gas, principally nitrogen, in the intervertebral disc of the spine [11]. Knutsson theorized that the pathophysiology of a vacuum disc was related to advanced arthrosis of the intervertebral disc. The vacuum phenomenon of the facet joint may also be related to advanced osteoarthrosis. Lumbar facet joint degeneration had been divided into five stages of degeneration process: synovitis, joint capsule laxity, articular cartilage thinning, subarticular bone change, and hyperostosis. Vacuum phenomenon with gas formation may occur secondary to the laxity of joint capsule [10], and may be extruded into the adjacent synovial cyst if it is present. It explains the atypical MR appearance of gas-filled synovial cyst. The differential diagnosis of intraspinal extradural lesions manifesting low signal characteristics on both T1-weighted and T2-weighted MR images include protruded osteophyte, gas-forming infection of the facet joint, crystal deposition of the ligamentum flavum, and, less likely, posteriorly sequestered disk fragment. The presence of swollen soft tissue edema and gadolinium-enhanced MRI may be helpful to distinguish gas-forming infection from the gas-filled synovial cyst. The locations of the sequestered disk fragments are usually ventral to the ligmantum flavum, while the synovial cysts are often at dorsal aspect of ligmantum flavum or inseparable from it [1]. Without other image modality such as CT, gas-filled synovial cyst may be indistinguishable from osteophyte or cystal deposition based on conventional MRI. Treatments of symptomatic synovial cysts usually consist of surgical resection, percutaneous aspiration or steroid injection, or immobilization using a brace [8]. Surgery is usually treatment of choice for such lesions due to its efficiency. However, spontaneous remission of the solitary intraspinal synovial cyst of the lumbar spine has also been reported [8]. Familiarity with the MR appearance of this unusual gas-containing synovial cyst can avoid the possibility of misinterpretation as intraspinal crystal deposition or giant osteophyte formation. In this report, we present a case of synovial cyst with vacuum and calcified rim of the lumbar facet joint, manifesting low signal intensity on both T1- weighted (666/18) and T2-weighted (4000/80) MR images. It may be misinterpretated as calcified nature such as crystal deposition or giant osteophyte if only MR images was used. The synovial cyst with vacuum of the facet joint should be included in the list of differential diagnoses when evaluating hypointense intraspinal extradural lesion adjacent to the facet joint on both T1-weighted and T2 weighted MR images. REFERENCES 1. Jackson DE, Atlas SW, Mani JR, Norman D. Intraspinal synovial cysts: MR imaging. Radiology 1989; 170: Liu SS, Williams KD, Drayer BP, Spetzler RF, Sonntag VK. Synovial cysts of the lumbosacral spine: diagnosis by MR imaging. AJNR 1989; 10: Yarde WL, Arnold PM, Kepes JJ, O Boynick PL, Wilkinson SB, Batnitzky S. Synovial cysts of the lumbar spine: diagnosis, surgical management, and pathogenesis. report of eight cases. Surg Neurol 1995; 43: Yuh WC, Drew JM, Weinstein JN, et al. Intraspinal synovial cysts: magnetic resonance evaluation. Spine 1991; 16: Resnick D, Niwayama G, Guerra J Jr, Vint V, Usselman J. Spinal vacuum phenomena: anatomical study and review. Radiology 1981; May; 139: Budris DM. Intraspinal lumbar synovial cyst. Orthopedics 1991; 14: Rosenblum J, Mojtahedi S, Foust RJ. Synovial cysts in the lumbar spine: MR characteristics. AJNR 1989; 10: S94 8. Maezawa Y, Baba H, Uchida K, Furusawa N, Kubota C, Yoshizawa K. Spontaneous remission of a solitary intraspinal synovial cyst of the lumbar spine. Eur Spine J 2000; 9: Spencer RR, Jahnke RW, Hardy TL. Dissection of the gas into an intraspinal synovial cyst from contiguous vacuum facet: case report. J Comput Assist Tomogr 1983; 7: Resnick D, Boutin RD. Apophyseal joint. In : Holger 160 Intraspinal synovial cyst of facet joint with vacuum Pettersson, David Allison. The encyclopaedia of medical imaging volume III:1 Musculoskeletal Imaging edition. Lund, Sweden: NICER Institute/Isis Medical Media, 1999; Abraham DJ, Vaccaro AR, Albert TJ, Cotler JM. Gas in the spinal canal associated with injury of the cervical spinal cord: a diagnostic dilemma, a case report. J Bone Joint Surg [Am] 1997; 79: Intraspinal synovial cyst of facet joint with vacuum 161
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