Annals of the Rheumatic Diseases 1995; 54: 539-543

CASE STUDIES IN DIAGNOSTIC IMAGING Series editor: V N Cassar-Pullicino*

Sciatica in degenerative spondylolisthesis of thelumbar spine

S Maheshwaran, AM Davies, N Evans, P Broadley, V N Cassar-Pullicino

Clinical historyA 57 year old female presented with a one yearhistory of low back pain and left sided sciatica.Her general health was unremarkable. Plainradiographs ofthe lumbar spine were abnormal(fig 1). These films revealed a spondylolisthesisat the L4/5 level. There was no evidence of anunderlying spondylolysis and the degenerativeL4/5 facet joints predisposed to the forwardlisthesis.The patient was given a lumbar support and

a course of physiotherapy. Although thesymptoms improved transiently, they graduallybecame worse, obliging her to give up her workas a secretary, because of constant back pain.She was referred for an MRI scan ofthe lumbarspine for further assessment.

Radiological findingsMagnetic resonance imaging (MRI) of thelumbar spine was performed (Siemens 1 TeslaImpact) using sagittal and axial Ti and T2weighted sequences. This revealed a soft tissuemass 1 cm in diameter on the medial aspect ofthe left L4/5 facet joint causing expansion ofthe lateral recess of L5 (fig 2A). The massexhibited intermediate signal intensity on theTi weighted sequences (fig 2A), and high

The MRI Centre,The RoyalOrthopaedic Hospital,Birmingham B31 2AP,United KingdomS MaheshwaranA M DaviesN EvansDepartment ofRadiology,The Robert Jones andAgnes HuntOrthopaedic Hospital,Oswestry, Shropshire,United KingdomP Broadley*VN Cassar-PullicinoCorrespondence to:Dr A M Davies.

signal intensity on the T2 weighted sequences(fig 2B, C). The left L4/5 facet joint wasdegenerate, with fluid evident within the jointas high signal intensity on the T2 weightedimages (fig 2B).

Precontrast computed tomography (CT)demonstrated the degenerate facet joints witha vacuum phenomenon on the left and anexpanded left lateral recess (fig 3A). Followingthe left L4/5 facet arthrogram, the CT showedcontrast medium within the facet joint and thesoft tissue mass (fig 3B).

DiagnosisLumbar intraspinal synovial cyst.

DiscussionThe lumbar intraspinal synovial cyst is anuncommon cause of low back pain or sciatica.'Since the advent of CT and MRI, theincreasing number of reports indicates thatthey are not as rare as originally considered andreflects the improved diagnostic accuracy ofdiagnostic imaging. The case described aboveis typical in that the majority of these cysts(approximately 60-75%) occur at the L4/5level, with the remainder at the L3/4 and L5/S 1levels.2 3 While the aetiology is unknown, it is

A BFigure I Present patient: Frontal and lateral radiographs of the lumbar spine showing degenerative spondylolisthesis at L4/5.

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Figure 3 Present patient. A: Axial computedtomography (CT) showing expansion of the left lateralrecess and a vacuum phenomenon in the facet joint. B:Axial CT afterfacet arthrography, showing the contrastmedium within the facetjoint and the synovial cyst.

Figure 2 Present patient. A: Axial Ti weightedfastspin-echo image (repetition time (TR) 700 ms, echo time(TE) 12 ms) showing a soft tissue mass expanding the leftlateral recess (arrowheads). B: Axial T2 weightedfastspin-echo (TR 3000, TE 158 ms) image showing the massto be ofhigh signal intensity with a low signal intensityrim. C: Left parasagittal T2 weightedfast spin-echo (TR3000 ms, TE 158 ms) image showing the synovial cyst as a

dumbell shaped lesion.

generally thought to be degenerative, withosteoarthritis of the adjacent facet joint auniversal finding, apart from the rare casesecondary to trauma or inflammatoryarthritis.4 5 The location of the cysts in theregion of maximum spinal mobility and theassociation of degenerative change suggest thatthey may arise as a result of chronic irritation.3The joint effusion bulges the joint capsule, andthe synovial membrane herniates through thejoint capsule-ligamentum flavum complex toform a synovial cyst. The term synovial cystalso refers to juxta-articular ganglion cystswhich do not communicate with joints.

CLNICAL FEATURES

Most patients present with chronic back painwith or without sciatica (symptoms ofdegenerative disc and joint disease). Thesymptoms are of increasing intensity. Theusual conservative measures of bed rest,physiotherapy, analgesics, and non-steroidalanti-inflammatory drugs (NSAIDs) fail torelieve the pain.6 There are some instances ofspontaneous resolution of symptoms, probablyas a result of collapse of the cyst. Theoccasional presentation with acute sciatica isindistinguishable from disc herniation. Thishas been attributed to the onset of haemor-rhage into the cyst.

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Sciatica in degenerative spondylolisthesis of the lumbar spine

I

Figure 4 Example ofa posterolateral compression of thelumbar theca seen in an oblique view of a myelogram.

IMAGING FEATURES

Plain radiographic changes are non-specific,but characteristically demonstrate a degenera-tive spondylolisthesis, as in this patient (fig 1).This is found in approximately 40% ofpatients.6 7 Although degenerative changes ofthe associated facet joint are seen in alldocumented CT cases, apart from the rarecases of post-traumatic origin or rheumatoidarthritis, the plain films may underestimate thefacet joint changes.8At myelography, a posterolateral extradural

impression on the column of contrast mediumis seen; figure 4 shows an example of this (notfrom the present patient). A similarappearance, however, may also be seen inhypertrophic facet joint degeneration. Thesechanges differ from the anterior oranterolateral indentation caused by a discherniation.8 The.appearances are non-specificand would be consistent with any extraduralspinal space occupying lesion at that site.On CT, fortunately, the majority of these

synovial cysts exhibit an attenuation value(greater than that of cerebrospinal fluid (CSF),but less than that of disc material) and areeasily identified. The associated facet jointalmost always shows degenerative changes.Increased attenuation may be seen if there hasbeen haemorrhage into the cyst, or in thechronic stage when peripheral or internalcalcification occurs.9 10 The rim of the cyst wallmaybe of high density attributable to eithercalcium deposition (fig 5C) or haemosiderin.Approximately 50% of the patients documen-ted in the literature who had undergone CTexamination had either a high density cyst wall

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Figure 5 A: Left parasagittal T2 weightedfast spin-echoimage (repetition time (TR) 4000 ms, echo time (TE) 112 ms)showing a lesion of heterogeneous signal intensity encroachingon the posterolateral theca at L4/5, together withspondylolisthesis. B: Axial T2 weightedfast spin-echo image(TR 4000 ms, TE 112 ms) showing bilateralfacet jointosteoarthritis, with high signal intensity in the left facetjointand a low signal intensity mass between the facet and the theca.C: Axial CT showing calkification within the synovial cyst.

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or calcification within the cyst.8 Synovial cystsare difficult to diagnose on CT if they are

isodense with the thecal sac. A negative attenu-ation can be found as a result of smallcollections of gas within the cyst, usually asso-

ciated with a vacuum phenomenon in theadjacent facet joint.8

Facet arthrography can be useful in patientsin whom the diagnosis remains in doubt,demonstrating the communication of the facetjoint with the synovial cyst.'0 Conventionalradiography may not reveal the small amountof contrast medium within the cyst and CT,immediately after the arthrogram, is thereforerequired.8The diagnosis on MRI is based on location,

morphology, and signal (MR) characteris-tics. As demonstrated by CT, these lesionsare rounded, well circumscribed epiduralmasses related to the anteromedial aspectof the degenerate facet joint (fig 2B).3 "

The MR signal characteristics of the intra-spinal synovial cyst are variable and depend on

the fluid composition and the MR sequences

used.The MR signal characteristics of the cyst

contents reflect its composition. Three basicpatterns can be identified. In the first type, thenon-haemorrhagic cyst, the signal intensity onthe Ti weighted spin-echo image is iso-intensewith that of theca (fig 2A). The signal intensityon the T2 weighted images may be slightlyhyperintense with respect to CSF (fig 2B, C)because of increased protein content. Inaddition, the motion in CSF will provide a

lower signal intensity than the static fluid in thesynovial cyst.3The second pattern occurs when contents of

the cyst are of low signal intensity on both theTI and T2 weighted images (fig 5A,B). Thismay be caused by either air or calcification inthe cyst. Differentiating this from a largeosteophyte on MRI alone may prove difficult.3CT is useful in this situation, as illustrated infigure 5C.The third, rarer, variety is the haemorrhagic

type, which contains breakdown products ofblood of differing ages. High signal intensity onTi weighted images may be attributable tomethaemoglobin as a result of subacutehaemorrhage, and the low signal intensity on

the T2 weighted images are caused byhaemosiderin from chronic haemorrhage.3 12

The plane of cleavage between the synovialcyst and the CSF is seen as a low signalintensity rim and it clearly separates the CSFfrom the contents of the cyst and is seen wellon the T2 weighted image in a type 1 cyst (fig2B,C). This rim may contain calcium whichmay be missed on MR but seen easily on CT.This is not the 'true rim' of the cyst and itappears to be the inflammatory interfacebetween the cyst and the dura. Rimenhancement seen after intravenous injectionof the paramagnetic contrast medium gado-linium-diethylene triamino pentacetic acid ischaracteristic.'3 It was present in all fivepatients reported by Yuh et al, with over 50/oalso showing enhancement within one or bothfacet joints." All three patients given gado-

linium in the series reported by Reginster et al7also showed rim enhancement.

DIFFERENTLAL DLAGNOSISThe differential diagnosis oflumbar intraspinalsynovial cyst includes conjoint nerve roots, alarge herniated disc with free fragments, otherintraspinal cysts, and cystic neurofibromata.These can be usually differentiated by thelateral location, associated degenerativechanges, and the signal characteristics.Although bone erosion is a typical feature ofneurofibromata, it may be present in anychronic process within the spinal canal with thepropensity to enlarge. This includes chronicdisc herniation,14 15 and synovial cysts'0 as inthis patient (figs 2A,3A).

MANAGEMENTThe correct diagnosis is important so thatappropriate management can be determined.'0Symptomatic relief may be achieved by facetjoint injection of local anaesthetic and steroidalone.'6 The effect of this is variable. If surgeryis required, a wider exposure than that for thetypical discectomy is required to identify theadherent dura mater above and below the cystin order to avoid surgical disruption of thedura.'7 During laminectomy the cyst maycollapse and the surgeon may not identify it.This may be a reason why synovial cysts werediagnosed infrequently before the availabilityof CT, as it is a non-specific diagnosis onmyelography.

SummaryIntraspinal synovial cysts are an uncommonbut well recognised cause of backache andsciatica, and should be considered in patients,in particular with degenerative spondylo-listhesis, who are symptomatic. MRI is theinitial investigation of choice. If there is anydoubt as to the diagnosis, CT with or withoutfacet joint arthrography is helpful.

1 Kiely M J. Neuroradiology case of the day: lumbar synovialcyst. Am_J Roentgenol 1993; 160: 1336-7.

2 Liu S S, Williams K D, Drayer B P, Spetzler R F,Sonntag V K H. Synovial cysts of the lumbar spine:Diagnosis by MR imaging. Am J Roentgenol 1990; 154:163-6.

3 Jackson D E Jr, Atlas S W, Mani J R, Norman D. Intraspinalsynovial cysts: MR imaging. Radiology 1989; 170:527-30.

4 Silberbleit R, Gerbaraski S, Brunberg J, McGillicudy J,Blaivas M. Lumbar synovial cysts: correlation ofmyelographic, CT, MR and pathological findings. Am J

Neuroradiol 1990; 11: 777-9.5 Awwad E E, Sundaram M, Bucholz R D. Post traumatic

spinal synovial cysts with spondylolysis: CT features. JfComputAssist Tomogr 1989; 13: 334-7.

6 Reust P, Wendling D, Lagier R, et al. Degenerative spon-dylolisthesis, synovial cyst of the zygapophyseal joints andsciatic syndrome: report of 2 cases and review of theliterature. Arthritis Rheum 1988; 31: 288-94.

7 Reginster P, Collignon J, Dondelinger R F. Synovial cystsof the lumbar spine: CT and MRI correlations. Eur Radiol1994; 4: 332-6.

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9 Hemminghytt S, Daniels D L, Williams A L, HaughtonV M. Intraspinal synovial cysts: natural history anddiagnosis by CT. Radiology 1982; 145: 375-6.

10 Lemish W, Apsimon T, Chakera T. Lumbar intraspinalsynovial cysts: recognition and CT diagnosis. Spine 1989;14: 1378-83.

11 Yuh W T C, Drew J M, Weinstein J N, et al. Intraspinalsynovial cysts: MR evaluation. Spine 1991; 16: 740-5.

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12 Summers R M, Quint D J. Case Report 712: Hemorrhagicsynovial cyst arising from the right L2IL3 facet joint.Skeletal Radiol 1992; 21: 72-5.

13 Wilms G, Hfkens L, Morlion J, et al. Bilateral lumbarintraspinal synovial cysts: Gd-enhanced MRI. Eur Radiol1993; 3: 471-3.

14 Vadala G, Dore R, Garbagna P. Unusual osseous changesin lumbar herniated discs: CT features. Comput AssistTomogr 1985; 9: 1045-49.

15 Flak B, U D K B, Knickerbocker W J. Case Report 567:Chronic disc herniation causing bone erosion. SkeletalRadiol 1989; 18: 481-2.

16 Bjorkengren A G, Kurz L T, Resnick D, Sartoris D J, GarfinS R. Symptomatic intraspinal cysts; opacification andtreatment by percutaneous injection. Am Roentgenol1987; 149: 105-7.

17 Onofrio B, Mih A. Synovial cysts of the spine. Neurosurgery1988; 22: 642-7.

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