DOI: 10.1148/radiol.2412040339
(Radiology 2006;241:618-621.)
© RSNA, 2006
Case 101: Lumbar Facet Synovial Cyst1
Daniel A. Marichal, MD,
J. Christopher Bertozzi, MD,
Glenn Rechtine, MD and
F. Reed Murtagh, MD
1 From the Departments of Radiology (D.A.M., J.C.B., F.R.M.) and Orthopaedic Surgery (G.R.), University of South Florida College of Medicine, Tampa, Fla. Received February 18, 2004; revision requested April 27; revision received May 12; accepted June 2; final version accepted July 23.
Correspondence: Address correspondence to D.A.M., 3500 Gaston Ave, Dallas, TX 75246 (e-mail: damarichal{at}earthlink.net).
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HISTORY
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An 82-year-old woman in otherwise good health experienced gradually increasing low back pain of 15 years duration that was caused by degenerative scoliosis. Bending or twisting worsened her pain, but it was generally well managed with exercise, an orthosis, and nonsteroidal antiinflammatory drugs. Recently, however, she began to experience bilateral leg pain. She underwent magnetic resonance (MR) imaging of the lumbar spine. On the basis of the MR findings, she returned to the clinic a few weeks later to undergo epidural steroid (0.5 mL betamethasone [6 mg/mL]) and facet joint (0.5 mL 1% xylocaine) injections with computed tomographic (CT) guidance. This resulted in the temporary resolution of bilateral leg pain. Approximately 2 months later, however, she returned to the clinic with low back pain radiating bilaterally to the legs. She subsequently underwent surgery.
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IMAGING FINDINGS
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Sagittal T1- and T2-weighted MR images of the lumbar spine showed a large mass with decreased signal intensity emanating from the L4-L5 facet joint and almost completely obstructing the spinal canal with grade 1 degenerative spondylolisthesis (Figs 1, 2). A transverse T2-weighted MR image of the lumbar spine showed a large mass with decreased signal intensity extending from the left L4-L5 facet joint space, with obstruction of the spinal canal (Fig 3). CT images of the lumbar spine were obtained with the patient in the prone position for CT-guided facet joint injections. These images revealed a mass with a high attenuation value, severe degenerative joint disease of the facets, and vacuum phenomenon of the intervertebral disk (Fig 4).
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Figure 1: Sagittal T1-weighted (repetition time msec/echo time msec, 500/14) spin-echo MR image of the lumbar spine shows a large low-signal-intensity mass (arrowhead) with a high-signal-intensity rim emanating from the L4-L5 facet joint and almost completely obstructing the spinal canal. Note grade 1 degenerative spondylolisthesis of the L4 vertebrae on the L5 vertebrae.
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Figure 2: Sagittal T2-weighted (3066/105) fast spin-echo MR image of the lumbar spine reveals a large low-signal-intensity mass (arrowhead) at the L4 through L5 spinal level with obstruction of the spinal canal. Note grade 1 degenerative spondylolisthesis of the L4 vertebrae on the L5 vertebrae.
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Figure 3: Transverse T2-weighted (3066/105) fast spin-echo MR image of the lumbar spine obtained through the cyst shows a large low-signal-intensity mass (arrowhead) extending from the left L4-L5 facet joint space, with obstruction of the spinal canal.
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Figure 4: Transverse CT scan of the lumbar spine obtained prior to facet joint injection at the L4 through L5 spinal level with the patient in the prone position reveals a somewhat high-attenuation mass (arrow), severe degenerative joint disease of the facets, and vacuum phenomenon of the intervertebral disk (arrowhead).
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DISCUSSION
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Surgical decompression of the mass confirmed the diagnosis of lumbar facet synovial cyst in this patient. Intraspinal synovial cysts are extradural lesions that arise from the synovial lining of the facet joints (1–4). The proposed mechanism of formation of these cysts includes repetitive microtrauma in association with abnormal spinal motion and degenerative joint changes, which leads to rupture of the synovial membrane, herniation of the synovial fluid and cells, proliferation of mesenchymal cells, and myxoid degeneration (1–4).
While synovial cysts can arise from any synovium-lined joint or tendon sheath, most cysts are found at the L4-L5 facet joint, as this is the level where the most biomechanical spinal motion occurs (1,2,4–6). Researchers have also found a relatively high frequency of degenerative spondylolisthesis in association with spinal synovial cyst formation (2,6).
Synovial cysts may extend into the neural foramen or spinal canal and result in symptomatic radiculopathy, spinal stenosis, or both (1). Patients may also experience neurologic claudication if the cyst is large enough to cause substantial compression of the spinal cord (4,7). Usually, unilateral symptoms affect the ipsilateral side on which the cyst is located; however, reports have shown that large enough cysts may cause symptoms on the contralateral side of the body secondary to compression of the contralateral nerve root (6). Such was the case in this patient.
The differential diagnosis for synovial cysts includes arachnoid cysts, perineural (Tarlov) cysts, schwannomas, and migrated herniated disk fragments (2,4,8). The MR imaging characteristics and the neuroanatomic location of the cyst help distinguish synovial cysts from these other lesions (2,3).
Extradural arachnoid cysts are cerebrospinal fluid–filled outpouchings of the arachnoid membranes that extend through a defect in the dura mater (2). Two-thirds of these lesions occur in the thoracic spine; this helps to differentiate these masses from synovial cysts, which occur most frequently in the lumbar spine (2,8). Perineural cysts can be distinguished from synovial cysts because perineural cysts are separate from the facet and are intimately associated with the nerve root (6,8). Likewise, schwannomas can be distinguished from synovial cysts on MR images by their intimate association with the nerve root; synovial cysts, on the other hand, emanate from the facet (8). Furthermore, the propensity for schwannomas to enhance homogeneously after administration of a gadolinium-containing contrast agent helps one distinguish this entity from synovial cysts, which typically demonstrate only rim enhancement (2).
Migrated disk fragments are sometimes found dorsal to the thecal sac, which complicates their differentiation from synovial cysts (8). They can, however, be distinguished reliably by their relationship to the ligamentum flavum, their signal intensity characteristics, and their lack of degenerative changes in the facet joint (2). Signal intensity in migrated disk fragments and synovial cysts is highly dependant on hydration of the disk material and the cyst contents, respectively (5;9, pp 1386–1387, 1394). Thus, location in relation to the ligamentum flavum is a more reliable characteristic for distinguishing migrated disk fragments from synovial cysts (2). Migrated disk fragments are typically located anterior to the ligamuntum flavum, whereas synovial cysts are located dorsal to or inseparable from the ligamentum flavum (8). Furthermore, migrated disk fragments are usually lobulated and have lower signal intensity on T2-weighted MR images than do the spherically shaped synovial cysts (2,8).
An air-filled synovial cyst can be mistaken for an osteophyte on MR images secondary to the signal void caused by air (2,8). A synovial cyst can fill with air secondary to the degenerative process in the adjacent joint whereby a negative pressure void allows dissolved nitrogen in the tissue to sublimate into the gaseous state (4;9, p 1408; 10). CT can be used to distinguish an air-filled synovial cyst from an osteophyte if they cannot be distinguished on MR images (3,8).
A lumbar facet synovial cyst typically appears as a sharply marginated epidural mass in which the contents most commonly appear isointense to cerebrospinal fluid on T1-weighted images and hyperintense to cerebrospinal fluid on T2-weighted images (2–4). The rim of a lumbar facet synovial cyst usually has a low signal intensity on T2-weighted images, while the signal intensity of the rim is more variable on T1-weighted images (2,3). Rim signal intensity on T1-weighted images is usually high, except when there is peripheral calcification or hemosiderin deposition, which leads to low rim signal intensity (1,3,4). While reports have noted that synovial cysts may appear hypointense on both T1- and T2-weighted images, these cases are uncommon and are usually caused by frank solid calcification of the cyst or vacuum phenomenon within the cyst that causes signal void (3). When these phenomena occur, they are distinguished easily by their appearance on CT scans (3,8). Consequently, this case was unusual in that the patient had a synovial cyst that had low signal intensity on both T1- and T2-weighted MR images and increased attenuation on CT images; these findings led us to believe that the cyst contents would contain calcified material.
Findings at subsequent surgery confirmed the diagnosis of a synovial cyst emanating from the left L4-L5 facet joint space that extended across the spinal canal and impinged the right lateral recess. The mass was atypical in that the contents of the cyst were firm and did not have the expected gelatinous consistency associated with most synovial cysts. Incision into the cyst revealed a dark viscous proteinaceous fluid, without evidence of hemorrhage. A thick glistening material that was consistent with hypertrophic synovium lined the cyst. Histologic examination of the cyst wall confirmed a synovial lining and revealed fibrous tissue with granulation tissue, inflammation, and adjacent fibrinoid debris. There was no evidence of calcium within the contents or the capsule of the cyst. While the presence of calcium pyrophosphate dihydrate crystals could have accounted for the CT and MR imaging characteristics of the cyst (11), the cyst contents were negative for birefringence when examined under polarized light. Furthermore, there was no evidence of hemosiderin deposition within the cyst, which led us to speculate as to the unusual MR and CT appearance.
One mechanism that could account for the unusual CT and MR appearances can be seen in third ventricular colloid cysts. Third ventricular colloid cysts appear hypo-, iso-, or hyperintense with respect to the brain on T1-weighted images, while most of these cysts appear hypointense on T2-weighted images (12,13). The MR signal intensity of third ventricular colloid cysts depends on the contents of the cyst, which can include old blood, hemosiderin, cholesterol crystals, cerebrospinal fluid, or paramagnetic ions (12). Paramagnetic ions are known to cause hypointense signal on both T1- and T2-weighted MR images. On CT scans, most colloid cysts have slightly increased attenuation with respect to brain parenchyma, although they occasionally may have the same or even decreased attenuation (13). Attenuation on CT scans correlates directly with the viscosity of cyst contents, which are known to contain an amorphous eosinophilic material that is strongly periodic acid–Schiff–positive secondary to glycogen and nonspecific proteinaceous material (12,13). Consequently, the CT and MR imaging characteristics of the described lumbar facet synovial cyst are nearly identical to those of third ventricular colloid cysts.
A report on third ventricular colloid cysts proposed that cholesterol esters contained within the cyst—and not paramagnetic ions—were responsible for the MR imaging characteristics of third ventricular colloid cysts (13). While specific chemical analysis for cholesterol esters was not performed for this cyst at the time of the pathologic examination, it is plausible that this same mechanism could account for the unusual CT and MR imaging appearances of the synovial cyst in the absence of calcification, calcium pyrophosphate dihydrate crystals, blood products, or inspissated secretions that could otherwise explain the MR imaging phenomenon (3,11,14).
In summary, lumbar facet synovial cysts are uncommon causes of low back pain and can be a cause of spinal cord compression, spinal segment instability, radiculopathy, and neurogenic claudication (1,2,4,6). These cysts are easily depicted with MR imaging and most commonly appear isointense on T1-weighted images and hyperintense on T2-weighted images (3,4). Attenuation of the cyst on CT images correlates directly with viscosity of the cyst contents (12). The MR imaging and CT characteristics, as well as the neuroanatomic location of the cyst, help to distinguish synovial cysts from other lesions (2,3). As in this case, unusual imaging findings do occur in patients with lumbar facet synovial cysts, and one must be careful to assign the correct diagnosis.
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ACKNOWLEDGMENTS
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The authors thank the University of South Florida Health Sciences Media Center for their help with assembling the images.
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FOOTNOTES
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| Part one of this case appeared 4 months previously and may contain larger images.
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References
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Congratulations to the 91 individuals and two resident groups that submitted the most likely diagnosis (lumbar facet synovial cyst) for Diagnosis Please, Case 101. The names and locations of the individuals and resident groups, as submitted, are as follows:
Individual responses
- Jorge Ahualli, San Miguel de Tucumán, Tucumán, Argentina
- Canan Altay, MD, Balcova, Izmir, Turkey
- Roger L. Antonelli, MD, Dayton, Ohio
- Lionel Arrivé, Paris, France
- Aaron Scott Bailey, MD, San Antonio, Tex
- Ken Baliga, Rockford, Ill
- Roberto Paes Barreto, Sr, MD, Recife, Brazil
- Ronald L. Becker, MD, Rolling Hills, Calif
- Richard Beedie, Auckland, New Zealand
- Daniel F. Broderick, MD, Jacksonville, Fla
- Douglas C. Brown, MD, Virginia Beach, Va
- Peter C. Buetow, MD, Bellingham, Wash
- Dr Marcelo F. Cabrini, Buenos Aires, Argentina
- Alan Dong Shing Chan, MD, West Sacramento, Calif
- Natesan Chidambaranathan, MD, Chennai, India
- Haris Chrysikopoulos, MD, Kerkyra, Greece
- Marco Antonio Cura, MD, San Antonio, Tex
- Thuan T. Dang, MD, Colton, Calif
- Marc G. de Baets, MD, Lugano, Switzerland
- Peter C. De Baets, MD, Damme, Belgium
- Jon James De Witte, Bishop, Ga
- Seena Dehkharghani, MD, Phoenix, Ariz
- Thaworn Dendumrongsup, MD, Hat Yai, Songkla, Thailand
- Seyed Emamian, MD, PhD, Rockville, Md
- Steven Falcone, MD, Weston, Fla
- Akira Fujikawa, Tokyo, Japan
- Rajneesh Galwa, Jaipur, India
- Ram Prakash Galwa, Chandigarh, India
- Pedro Garcia, MD, Gijon, Spain
- Douglas Joseph Gardner, MD, Windsor, Ontario, Canada
- Fouad Gellad, MD, Timonium, Md
- D. M. Ghookal, MBBCh, Regina, Saskatchewan, Canada
- Francisco Jose Gonzalez, MD, Cantabria, Spain
- Dan G. Gridley, MD, Phoenix, Ariz
- Flavius Guglielmo, MD, Basking Ridge, NJ
- Rekha Gupta, Sr, MD, Panchkula, India
- Ferris M. Hall, MD, Boston, Mass
- D. Cressler Heasley, Jr, MD, Dallas, Tex
- Lloyd E. Heller, Jr, MD, Portland, Ore
- Helen T. Ho, MD, Chicago, Ill
- Waleed Ibrahim, MD, Detroit, Mich
- Rajapandian Ilangovan, MD, FRCR, London, United Kingdom
- Kiriakos Kalampoukas, MD, Athens, Greece
- Koki Kato, Tochigi, Japan
- Nurettin Katranci, MD, Antalya, Turkey
- Steven A. Klein, MD, Shrewsbury, Mass
- Mehmet Kocak, MD, Milwaukee, Wis
- Stefanos Lachanis, MD, Athens, Greece
- Alexis Lacout, MD, Paris, France
- Alan Laorr, MD, Eden Prairie, Minn
- Walter S. Lesley, MD, Temple, Tex
- David A. Lisle, Brisbane, Australia
- Naganathan B. S. Mani, MD, Nassau, Bahamas
- Paulo Mariz Filho, MD, Salvador, Buenos Aires, Brazil
- Michael B. Martin, MD, Austin, Tex
- Frank McKowne, MD, Vancouver, Wash
- Edward Menges, MD, Aptos, Calif
- Nikolaos Michailidis, MD, Thessaloniki, Greece
- Mansour Mirfakhraee, MD, Shreveport, La
- Sankar Ranjan Mondal, MD, Nassau, Bahamas
- Tammam Naim Nehme, MD, East Wenatchee, Wash
- Albert Nizzero, MD, Sudbury, Ontario, Canada
- Marcos Nogueira Chagas, MD, Brasilia, Brazil
- Laura Oleaga, MD, Bilbao, Spain
- Michael Opatowsky, MD, Dallas, Tex
- Sanford M. Ornstein, MD, Phoenix, Ariz
- Harish Panicker, MD, Hermitage, Pa
- Prakash N. Patel, MD, New City, NY
- Ernesto Oscar Pearson II, MD, Besançon, France
- Carlo Lucius E. Petralli, MD, Bruderholz, Switzerland
- John M. Plotke, MD, Naperville, Ill
- Ryan Paul Rebello, MD, Dundas, Ontario, Canada
- Enrique Remartinez Escobar, MD, Melilla, Spain
- Matthew C. Rheinboldt, MD, Nashville, Tenn
- Marcio Bustamante Sa Rodrigues, MD, Rio de Janeiro, Brazil
- Gerald Ross, Sewickley, Pa
- Kris B. Saadeh, MD, Mount Pleasant, SC
- Steven M. Schultz, MD, Fort Worth, Tex
- Matt Shapiro, MD, Charlottesville, Va
- Hideki Shima, MD, Tokyo, Japan
- Taro Shimono, MD, Sakai, Osaka, Japan
- Grady Shue, Jr, MD, Hickory, NC
- Sanjay Kumar Singh, MD, Friendswood, Tex
- Darrin Smith, MD, Tulare, Calif
- David F. Sobel, MD, La Jolla, Calif
- Marius Stellmann, MD, Stade, Germany
- Kazuma Terauchi, Fujieda, Shizuoka, Japan
- Eleni Vafeiadou, Thessaloniki, Greece
- Bonny Varghese, MD, Abu Dhabi, United Arab Emirates
- Ensar Yekeler, MD, Istanbul,Turkey
- Thomas T. Zacharia, MD, New York, NY
Resident group responses
- Hospital Italiano Córdoba Radiology Residents, Córdoba, Argentina
- University of Pennsylvania Radiology Residents, Philadelphia, Pa
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TOP
HISTORY
IMAGING FINDINGS
