review article intra-articular and peri-articular tumours...

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Abstract Definitivedeterminationofthecauseofarticularswellingmaybedifficultbasedonjusttheclinicalsymptoms,physicalexaminationsandlaboratorytests.Jointdisordersfallundertherealmsof rheumatology and general orthopaedics; however, patients with joint conditionsmanifestingprimarily as intra-articular and peri-articular soft tissue swelling may at times be referred toan orthopaedic oncology department with suspicion of a tumour. In such a situation, an onco-radiologistneedstothinkbeyondtheusualneoplasticlesionsandconsiderthediagnosesofvariousnon-neoplastic arthritic conditions that may be clinically masquerading as masses. Differentialdiagnosesofarticularlesionsincludeinfectiousandnon-infectioussynovialproliferativeprocesses,degenerativelesions,depositiondiseases,vascularmalformations,benignandmalignantneoplasmsand additionalmiscellaneous conditions.Many of these diseases have specific imaging findings.Knowledgeof theseradiologicalcharacteristics inanappropriateclinicalcontextwillallowforamoreconfidentdiagnosis.

Keywords: intra-articular, peri-articular, synovial, tumours

Introduction

Inadditiontobenignandmalignanttumoursoftheepimetaphysealregionsofbone,synovium,and juxta-articular soft tissues,awidespectrumof infectious and non-infectious processes ofthe joints may present as intra-articular andperi-articularmasses (Table 1) (1,2).Thisarticlereviews the typical imaging features of variousintra- and peri-articular masses and mass-likelesions with special emphasis on the magneticresonance imaging (MRI) findings that suggesta specific diagnosis. It aims to equip the readerwithapragmaticapproachtoimagingofpatientspresentingwithsuspectedtumour-likeswellinginandaroundjoints.

Benign and malignant tumours of bone and juxta-articular soft tissues

Almost any tumour arising from epi-metaphyses of longbones or juxta-articular softtissuesmaymimica joint swelling.Examplesofbonetumoursthatcommonlyariseinthislocationinclude chondroblastoma and aneurysmal bonecyst in the younger population and giant celltumour,clearcellchondrosarcomaandmalignantfibrous histiocytoma in adults (Figure 1). Extra-osseous soft tissue involvement by malignanttumours and synovial effusion resulting from

Review Article Intra-articular and Peri-articular Tumours and Tumour Mimics- What a Clinician and Onco-imaging Radiologist Should Know

Sunita DhanDa, Swee Tian Quek, Girish Bathla, Pooja Jagmohan

Department of Diagnostic Imaging, National University Hospital, 5 Lower Kent Ridge Wing, Singapore 119074

Submitted:7Dec2013Accepted:9Feb2014

intra-articular tumour extension or sympatheticresponsemayalsoresultinperi-articularand/orjointswelling(3). A wide spectrum of benign and malignantsoft tissue neoplasms may occur in the peri-articularlocation.Amongthese,synovialsarcoma

Figure1:Antero-posteriorandlateralradiograph(a,b)oftherightkneeinapatientwithparostealosteosarcomawhopresentedwith painful knee swelling andrestrictionofmovement.

4Malays J Med Sci. Mar-Apr 2014; 21(2): 4-19

mailto:sunitadhanda63%40gmail.com%20?subject=

Review Article |Intra-articularandperi-articulartumorsandtumormimics

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deservesaspecialmentionasithasapredilectionforjuxta-articularsofttissues(2).Itisdiscussedindetailunderthesynovialmalignancies.

Benign Synovial Tumours

Lipoma True intra-articular lipomas are extremelyrarelesions.(4)Unlikelipomaarborescens,atruelipoma is a solitary round or oval lesion and iscomposedofmatureadiposetissueenclosedbyathinfibrouscapsule(Figure2).Itmaybecoveredbysynovialtissueandmayhaveavascularpedicle.Villous proliferation of the synovial membraneis absent. True lipomas of the knee joint aregenerally located in relation to the subsynovial

Table1:Classificationofconditionsthatmaypresentclinicallyas intra-articularandperi-articularmasses

Etiology Condition DifferentialdiagnosesNeoplastic Benign&malignantneoplasms Osseousorigin:

Anyprimaryneoplasmsuchasosteogenicsarcomaetc.Metastases

Extra-osseoussofttissueorigin:SynovialsarcomaSynovialchondrosarcomaSynovialmetastasesSynovialchondrolipomaSynovialliposarcomaetc.

Non-neoplastic Noninfectioussynovialproliferativeprocesses

PigmentedvillonodularsynovitisSynovialosteochondromatosisLipomaarborescens

Infectiousgranulomatousdiseases

TuberculararthritisFungalarthritis

Depositiondiseases GoutAmyloidarthropathy

Inflammatoryconditions RheumatoidarthritisChronicasepticsynovitisBursitisTenosynovitisofperiarticulartendons

Degenerativelesions SynovitisGanglionsCystsLoosebodies

Vascularmalformations SynovialhemangiomaArterio-venousmalformations

Miscellaneousconditions NeuropathicarthropathyHemophilicarthropathyLipohemarthrosisCyclopslesion

fatoneithersideofthepatellarligamentoroverthe anterior surface of the femur (5–8). Intra-articularlipomasareusuallynon-calcifiedmassesthatarepredominantlyhyperintenseonbothT1andT2-weightedimages(4,9,10).

Synovial malignancies

Synovial Sarcoma Synovial sarcoma is a mesenchymalneoplasm named because of its resemblanceto synovial tissue under light microscopy (2).Despite its name, fewer than 5% of lesions areintra-articular in origin; instead, they usuallyoccurnearjoints(2).Mostsynovialsarcomasarelocatedintheextremities,withtwo-thirdsinthe

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Malays J Med Sci. Mar-Apr 2014; 21(2): 4-19

Figure2:Chondrolipomaoftheknee.A29-year-oldmalepatientpresentedwithapainless,non-tenderswellingon the lateral aspectof the leftknee.AxialT2-weighted (a), coronalT1-weighted(b) and fat suppressed proton density (PD)weighted (c) images show awell-defined pearshapedfatsignalintensitylesionwithmultipleinternalcurvilinearhypointensitiesdeeptothelateralpatellarretinaculumandextendingbeneathvastuslateralismuscleconsistentwithanatypicallipomatouslesion.Biopsyandhistopathologicexaminationofthesurgicalspecimendemonstratedachondrolipoma.

Figure3:A16-year-oldboypresentedwithanindolentswellingontheposterioraspectoftherightknee.Lateralkneeradiograph(a)revealsanill-definedsofttissuedensitymassinthepoplitealfossawithnoobviouscalcifications.AxialT1andT2-weightedmagneticresonanceimages(bandcrespectively)showaheterogeneous,multilobulatedjuxta-articularmassinthepoplitealfossa(arrowheads)withseptationsandcysticareas.Oneofthelobulesdemonstrateshyperintensesignal onT1 andfluid levels onT2-weighted image (arrows) compatiblewithhemorrhage.Histopathologyexaminationdemonstratedabiphasicsynovialsarcoma.

lowerextremities.Theyparticularlyoccuraroundthekneeinthepoplitealfossaofadolescentsandyoungadults(15–40yearsofage).Radiographicfeaturesofthesetumoursarenotpathognomonic.However,asoft-tissuemassnearajointofayoungpatient, particularly a calcified lesion (30%), issuggestive of the diagnosis (2,11). On MRI, thelesion ishypointenseonT1-weighted(T1W)andhyperintense on T2-weighted (T2W) imagesand demonstrates multilobulation and markedheterogeneity (creating the “triple sign”) with

haemorrhage,fluidlevelsandsepta(creatingthe“bowl of grapes” sign) (Figure 3) (2,11,12). Slowgrowth(averagetimetodiagnosis,2–4years)andsmall size (<5cmat initialpresentation)of thelesionmayresultinamistakeninitialdiagnosisofabenignindolentprocess(11).

Synovial Metastases Metastatic spread of tumours to the jointsandsynoviumisrare,despitethehighlyvascular


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Figure 5: Synovial chondrosarcoma in a 71-year-old man presenting with a gradually progressive,mildlypainfulkneeswellingandlimitationofmovement.Lateralradiographsoftherightknee;(a)demonstratesanintra-andperi-articularmasswithchondroidpatternofmatrixmineralization. Sagittal and axial T2-weighted images, (b and c respectively) confirm thesynovialoriginofthemasswithapredominantextra-articularcomponent,extendingintosurrounding soft tissues and causing large bony erosions (arrows), features favoring anaggressive behavior.Themass shows a lobulated appearancewithheterogeneouslyhyperintensesignalintensityonT2-weightedimages.Biopsyofthemassdemonstratedalowgradechondrosarcoma.

nature of the synovium (13–17). Metastaticarthritis can involve the synovium, the jointcartilageorboth (Figure4). It can reflect eitherdirect metastatic invasion of the synovium orreactive synovitis causedby juxta-articularbonemetastases (13–17). The most frequent primarytumour that metastasises to the joint is lungcarcinoma,withadenocarcinomabeingthemostcommonhistologicaltypeandthekneebeingthemost commonly involved joint (13). Diagnosis

can be made with either joint fluid cytology orsynovialbiopsy.Theprognosis is generallypoorwithabysmalsurvivalrates(13,16).

Rare malignancies Although exceedingly rare, primaryintra-articular liposarcoma and synovialchondrosarcoma (Figure 5) have been reportedin literature, usually involving the knee joint(18–20).

Figure4:A54-year-oldmanwithdisseminatedcoloncancerpresentedwithafocal,hardswellingonthemedialaspectofleftknee.AxialT1,T2andfatsuppressedPD-weightedimage(a,bandcrespectively)showalobulatedsofttissuemassinmedialpatello-femoralcompartmentoftheleftknee,involvingmedialpatellarretinaculumandcausingerosionofmedialborderofpatella.ThemassshowsisointensesignaltomuscleonT1andhyperintensesignalintensityonT2andfatsuppressedPD-weightedimages.Biopsyexaminationofthelesiondemonstratedadenocarcinomawithhistologyidenticaltotheprimarylesionincolon.

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Figure6:A34-year-oldmanwithalargefluctuantrightkneeswelling.SagittalT1andfatsuppressedT2-weightedimagesoftheknee(aandbrespectively)demonstratealobulatedprofoundlyhypointensemassinthekneejoint,predominantlyalongposterioraspectwithevidenceofmagnetic susceptibilityartifacts (blooming)on sagittal gradient image (c), consistentwiththediagnosisofapigmentedvillonodularsynovitiswhichwasconfirmedonhistopathologyexamination.Post-gadoliniumT1-weightedimage,(d)revealsintenselyenhancing,markednodularthickeningofthesynovium.

Non-Infectious Synovial Proliferative Processes

Pigmented villonodular synovitis (PVNS) PVNS is a benign proliferative disorder ofthe synovium thatmay affect the joints, bursaeor tendon sheaths (1,2,21,22). It usually occursin the third and fourth decades of life, with nogender predilection (1). The condition can belocalisedordiffuse(2).Whentheentiresynoviumofthejointisaffectedandthereisamajorvillouscomponent,theconditionisreferredtoasdiffusepigmented villonodular synovitis. Presence of adiscrete intra-articular mass is called localisedpigmented villonodular synovitis. PVNS of thetendon sheath is known as giant cell tumour ofthetendonsheath(21–24).Thekneeisthemostfrequently affected joint followed by the hip,ankleandshoulder(1,2).DiffusePVNSpresentsclinically as chronic monoarthritis, commonlywith haemarthrosis (1,21,22), and is treatedby total synovectomy with a tendency for localrecurrence. The focal form is effectively treatedwith resection. Radiosynovectomy has beenused as an alternative treatment option, usuallyfor the diffuse form in which complete surgicalresectionmaybeproblematicandtheriskoflocalrecurrencepost-surgeryishigher(21,22,25,26). Radiographsmaybenormalordemonstratesofttissuemassesthatmayappeardenseduetohigh hemosiderin deposition. It virtually nevercalcifies. Preservation of bone mineralisationand joint spaces until late in the disease ischaracteristic (1,2,21). Bony erosions arefrequent in joints with a tight capsule, such asthehip,ankleandelbow(1,2,22).MRimagesof

diffuse PVNS show typical lobulated mass-likesynovial proliferation, appearing hypointenseon T1 and T2-weighted images (1,2,21) andshowing characteristic “blooming” on gradientecho images due to hemosiderin deposition(1,21)(Figure6).The“bloomingartefact”isveryeffective in distinguishing it from other entitiessuch as gout, amyloid arthropathy, chronicrheumatoid arthritis, chronic granulomatousdisease, synovial sarcoma, and synovialchondromatosis. Haemophilic arthropathy mayalsoshowhemosiderindepositionbutcanbeeasilydistinguished clinically (1,21,22,27). However,hemosiderin deposition is less pronounced inolder fibrotic lesions and focal forms of PVNS,rendering the diagnosis more difficult. T2Wimagesmayalsoshowhyperintenseareasduetoinflamedsynoviumandjointeffusions(21,22,24,28–31).

Synovial osteochondromatosis Synovial osteochondromatosis is a benigncondition of uncertain aetiology, characterisedby proliferation andmetaplastic transformationof the synovium and formation of multiplecartilaginous or osteocartilaginous noduleswithin the joints, bursae or tendon sheaths(1,2,32–34).Itusuallyoccursinthethirdtofifthdecade of life and is twice as common in men.Clinical manifestations include pain, swellingand limitation of motion (1,2,32,33). It mostcommonly involves the knee joint followed bytheelbow,hipandshoulder(1).Thenodulesmaycontainonlycartilage,bothcartilageandboneormaturebonewithfattymarrow.Calcificationandossificationofnodulesisnotedin70–95%ofcases


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Figure 7: Synovial osteochondromatosis ina 40-year-old man presentingwith right shoulder joint pain andrestriction of movement. Antero-posterior radiograph of shoulderrevealsinnumerable,uniformsized,ossifiedintra-articularloosebodiesat the glenohumeral joint and itssynovial recesses. Note ismade ofpreserved joint space and absenceof significant degenerative jointchanges.

Figure8: Synovial chondromatosis inapatientwithbilateralkneepain.Frontal radiographofbothknee joints (a) revealsmultiple similar sized intra-articular loose bodies. Sagittal PD (b),gradient(c),andfatsuppressedT2-weightedimages(d)revealsynovialproliferationwithintra-articularcalcifiedandossifiedloosebodiesdemonstratinguniformlyhypointensesignaland centralmarrow signal intensitywithwell corticated profoundly hypointensemarginsrespectively.

(1,32).Whenthenodulesareossified,radiographsarediagnostic(2,32)(Figure7).MRIissuperiortoconventionalradiographyforassessingdiseaseextent due to its ability to demonstrate earlyintra-synovial metaplastic nodules and non-mineralisedloosebodies(32).MRappearanceisvariabledependingon therelativeproportionofsynovialproliferationandnodulemineralisation(2). Non-calcified nodules are observed asconglomeratemassesofisointensesignalrelativeto muscle on T1W images and bright signal onT2W images. Calcified nodules are observed ashypointense foci with all pulse sequences whileossifiedloosebodiesdisplaycentralhyperintensefattymarrowandperipheralhypointensecorticalbone(2)(Figure8).Onpost-gadoliniumimages,the metaplastic cartilaginous nodules mayshow the characteristic peripheral and septalenhancementof chondral lesions (1).Associatedsynovial effusion and bony erosions are betterdepictedwithMRimaging(32).Theconditionistreatedwithsurgicalsynovectomy,butrecurrenceiscommon(32).Secondaryosteoarthritisisalatecomplication(32).

Lipoma arborescens Lipomaarborescensisararenon-neoplasticintra-articular lesion characterised by villoussynovial proliferation and replacement ofsubsynovialtissuebymaturefatcells(2,35,36).Itusuallyoccurs in thefifth to sixthdecadeof lifeand ismore common inmen (2).Theconditionis usually monoarticular and most frequentlyinvolves the knee, particularly the suprapatellarpouch (2,35,36). It presents clinically as a long-standing, painless and slowly progressive jointswelling (2,36). Lipoma arborescens has been

hypothesisedtorepresentanon-specificsynovialreaction to inflammatory (2,36,37) or traumaticstimuli (2,36). It is treated with surgical orarthroscopic synovectomy (2,37). Radiographs

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Figure9:Lipomaarborescenceina46-year-oldmanwithrecurrentkneejointswellingand pain. Sagittal T1 (a) and fatsuppressed T2-weighted (b) imagesof theknee jointrevealmildsynovialeffusion and prominent subsynovialfat along with frond-like projectionsintothesynovialspaceofsuprapatellarbursa, showing hyperintense signalonT1W image and signal loss on fatsuppressedimagecompatiblewithfatcontainingvilli.

Figure 10: Tuberculous arthritis. Axial fatsuppressed post gadolinium T1-weighted image of the knee jointreveals markedly thickened andenhancing synovium (arrows)with effusion and loculations.Abbreviations: P = patella, F =femur.

arenon-specific(2).Onultrasound,itisobservedasahyperechoicfrond-likesynovialmasswithinan effusion; the mass may move with jointmanipulation(2).MRallowsaspecificdiagnosisbydemonstrating characteristic villous lipomatoussynovial proliferation andmass-like subsynovialfatdepositsassociatedwithjointeffusion(35,38)(Figure9).Differential diagnosis should includesynoviallipomaandsynovialhaemangioma.

Chronic Infectious Arthritis

Tubercular arthritis Musculoskeletal tuberculosis maymanifest as osteomyelitis, spondylitis, arthritis,tenosynovitisorbursitis(2).Tuberculararthritisusually results from haematogenous spread ofinfection to thesynoviumor, lesscommonly,bydirect intra-articularextensionfromanadjacentfocus of osteomyelitis (2,39). It is usually achronicmonoarthritisandmostcommonlyaffectsaweight-bearingjointsuchasthehip,kneeandankle(39). No radiographic feature is pathognomonicfor tubercular arthritis (40). Juxta-articularosteoporosis, marginal erosions, gradualnarrowing of intra-articular space, soft-tissueswelling and joint effusions are the mostcommonly described findings (2,39–41). Incontrast to rheumatoid arthritis, the joint spaceisrelativelypreservedinearlytuberculararthritisdue to gradual late destruction of the articularcartilage(40).MRIrevealssynovialhypertrophy,typically with intermediate to low T2W signalintensity and intense contrast enhancement(41). It canalsodemonstrateassociatedmarrowoedema,osteomyelitis,corticalerosions,myositis,cellulitis, abscesses, and skin ulceration/sinusformation in the adjacent bone and soft tissue(Figure9)(41).Ricebodiesmayalsobeobservedin tuberculosis (42). MRI may be helpful indistinguishing rheumatoid from tuberculararthritis(40).AlthoughthereissignificantoverlapinMRappearancesbetween the twoconditions,tubercular arthritis tends to havemore uniformsynovial thickening (Figure10)with largerboneerosions,rimenhancementatthesiteoferosionand extra-articular cystic components. Clinicalimagingdifferentiationbetweentuberculosisandpyogenicarthritismaybedifficult.Aspirationofsynovial fluid is often insufficient to make thedistinction, and an accurate diagnosis usuallyrequires synovial biopsy and histopathology orculture(39).

Deposition Diseases

Gout Goutisametabolicdiseasethatresultsfromlongstandinghyperuricemia,leadingtodeposition


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ofmonosodiumurate(MCU)crystalsinjointsandsoft tissues (43–45). Itoccursusually in the5thto7thdecadesoflifewithamalepreponderance(43,44). The first metatarsophalangeal (MTP)joint is involved in half of the cases at the firstattackand is themost frequently involved joint.First presentations are usuallymonoarticular innature.Thefrequencyanddurationofattacksaswell as number of affected joints increase withdisease progression. Gout has a predilectionfor joints of the extremities; feet, elbows andwristsareaffectedmostcommonly.However,noperipheraljointisexempt.Thediseaseaffectsthelowerextremitiesmorethantheupperextremitiesandsmalljointsmorethanlargejoints.Goutmaymanifest radiographically as acute, intermediateorchronicforms.Tophusisahallmarkofchronicgout(44).Itrepresentsdepositionofurate,proteinmatrix, inflammatory cells and foreign bodygiant cells in intra-articular space,peri-articularsubcutaneous tissues, tendons, ligaments,cartilage, bone and other soft tissues includingbursaeandothersynovialspacesinpatientswithlong standing disease. Chronic tophaceous goutmay present clinically as intra-articular or peri-articularmasses(45).Characteristicradiographicfeaturesof chronicgoutyarthritis include juxta-articular erosions with overhanging margins,eccentricsofttissueswellingandpreservationofjoint spaceuntil late in thedisease (43–45).OnMRI,tophicharacteristicallyshowhomogenousorheterogeneouslowtointermediatesignalintensityonbothT1andT2Wimages,althoughthesignalintensityonT2Wimagesmaybevariable(Figure

11). Gadolinium-enhanced images demonstratean intense homogenous, heterogeneous orperipheral enhancement of tophi (1,46,47).Computed tomography (CT) is more specific indiagnosis of tophi, which are typically observedashyper-densemassesofapproximately160HUattenuation values or above, corresponding toMSUcrystaldeposits(43,47–49).

Amyloid arthropathy Amyloid arthropathy is characterised byamyloid deposition in intra-articular and peri-articular tissues (1,2). It is most commonlyobserved in amyloidosis related to long-termhaemodialysis or plasma cell dyscrasia and lesscommonlywithchronicinflammatoryconditions(2). Amyloid arthropathy is manifested byerosive and destructive osteoarthropathies,most frequently affecting the hips, wrists,shoulders, knees, and spine. Destructivespondyloarthropathy and carpal tunnelsyndrome occur predominantly in dialysis-related amyloidosis (1,2,50). Well-defined non-mineralisedcysticlesionswiththinscleroticrims,representingosseousamyloidomas, are typicallyobserved in bilateral peri-articular bones andat ligamentous insertion sites (Figure 12) (50).Characteristic findings of amyloid arthropathyinclude juxta-articular soft tissue masses, peri-articularosteopenia,subchondralcysts,andjointeffusionsandpreservationofjointspaceuntillatein thedisease.Otherradiographicabnormalitiesinclude joint destruction, subluxations anddislocations and digital contractures (50). On

Figure11:Knowncaseofchronictophaceousgoutpresentingwithleftankleswelling.Frontalradiographoftheleftankle(a)revealssofttissueswelling(asterisk)inmedialsubmalleolarregionwithwell-definederosion(arrow)ofthetipofmedialmalleolus.Softtissuefullnessisalsonotedonthelateralaspect.CoronalT1(b),T2-weighted(c)andaxialgradientecho(d)magneticresonanceimagesdemonstratejuxta-articularerosionsofmedialandlateralmalleolusandtalus (arrowheads ind)withpreserved joint spaceandassociatedeccentric intra-articulartophaceousdeposits(arrows)showingcharacteristicheterogeneouslowsignalintensityonT1andT2-weightedimageswithabsenceof“blooming”ongradientimage.

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Figure 12: Biopsy-proven dialysis relatedamyloidosis in a 70-year-oldman on hemodialysis for 21years for diabetic nephropathy.Coronal computed tomography(CT) image of abdomen (a)reveals end stage renal diseasewith severe atheroscleroticvascular calcification. Axial CTimageatthelevelofhipjoints(b)demonstrates well-defined cysticlesionswithscleroticriminbothfemoral heads and right femoralneck communicating with thejoint space and intra-articularamyloiddeposits.

MRI, the amyloid deposits characteristicallyexhibit intermediate to low signal intensity onbothT1andT2Wimages,althoughsignalintensityonT2sequencemaybevariable(1,2).MRIallowsassessment of the extent and distribution ofintraosseous, peri-articular and intra-articularsoft-tissue involvement. Biopsy, althoughconfirmatoryfordiagnosis,isnotalwayspossible.Hence, clinical radiologic correlation is used formaking an early and precise diagnosis beforeserious complications arise, such as pathologicfractureorcompressivemyelopathy(50).

Inflammatory Conditions

Various non-infectious inflammatoryconditions suchas rheumatoidarthritis, chronicaseptic synovitis, bursitis and tenosynovitis ofperi-articulartendonsmayalsopresentas joint-related swelling.Rheumatoidarthritismanifestsas bilateral symmetrical erosive polyarthritis,most commonly affecting hands, wrists andfeet (2,51) in the fourth to sixth decadeswith afemale preponderance (2). Diagnostic criteriainclude typical clinical radiographic findingsand serum rheumatoid factor levels (51).Radiographs demonstrate a diffuse, usually

multi-compartmental, symmetric narrowingof the joint space associated with marginal orcentral erosions, peri-articular osteoporosis andsoft-tissue swelling, not usually associated withsubchondral sclerosis or osteophyte formation(2). The inflammatory response in rheumatoidarthritis results in proliferative, hyperplasticand hypervascular synovium called pannus thatcauses bony erosions. It is observed as low tointermediatesignalintensityintra-articularmasswithbothT1 andT2WMR images.Unlike jointeffusion, active pannus shows intense contrastenhancement (2,51). Patients with rheumatoidarthritis may demonstrate synovial rice bodies(Figure 13), representing detached synovial villiwithinthejointcavitythatresemblegrainsofriceand contain coarse collagenous fibres, reticulinandelastin(51).

Vascular Malformations

Synovial haemangioma is an uncommonbenign vascular tumour of children and youngadults which can involve the joint in a focal ordiffuse fashion (2,52). Itmay be either synovialand/or juxta-articular in location (53). Patientspresentwithjointpain,swellingandspontaneoushaemarthrosis (2). Conventional radiographsmayrarelydemonstratephlebolithsallowingthediagnosis to be made (2,54). More commonly,however, theyareeithernormalordemonstratenon-specificfindingssuchassofttissueswelling/mass, advanced maturation of the epiphysis,muscleatrophyandlimblengthdiscrepancy(55).MRIfeatures,however,arehighlycharacteristic.It is observed as a lobulated intra- or juxta-articularmassofintermediatesignalintensityonT1WimagesandhyperintensesignalT2Wimagesdue to pooling of blood in vascular spaces withtypical internal linear lowintensitywithin,mostlikely due to flow voids or fibrous septa (Figure14)(2,54–56).Afluid-fluidlevelmaybenotedincavernous-typelesions(56).MRIisthereforetheprocedureofchoiceinasuspectedcaseofvascularintra-articular lesions and can obviate the needfor conventional angiography. It can preciselydelineatethelocationandextentofthelesionforsurgicalplanning(54). Arterio-venous malformations (AVMs)(arterio-venous malformations) are congenitallesionscharacterisedbyanabnormalconnectionbetween arteries and veins. There is a centralconfluence of tortuous vessels, called a nidus,throughwhich arterial blood is shunteddirectlyinto veins. Diagnosis of intra-articular AVMson various imaging modalities is based on


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Figure14:A17-year-oldboywithapalpablelumpontheposterioraspectoftheleftknee.Lateralkneeradiograph(a) revealsa soft tissuemasswithbizzarecalcificationon itsposterioraspect.SagittalSTIRMRimage(b)showsajuxta-articularhyperintensemasswithmultipleroundwell-defined hypointense fociwithin suggestive of phleboliths. Axial post-gadoliniumT1-weightedimage(c)demonstratesavidcontrastenhancementwithinthemasswithinfiltrativemargins.CoronalT1-weightedimagerevealsfewhyperintensefociwithinthemass(arrows).Biopsydemonstratedasynovialhemangioma.

demonstration of a hypervascular lesion with alargefeedingarterialvessel.Intra-articularAVMsarelesscommonthanextremityAVMs(2,56).

Miscellaneous

Neuropathic osteoarthropathy Neuropathic osteoarthropathy refers to thedestruction of bones and joints associated witha central or peripheral neurosensory deficit,mainly loss of proprioception. This subjects thejointtochronic,unrecognisedwearandtear.Thecausative conditions include diabetes mellitus,syringomyelia, syphilis, leprosy, spinal cordlesionorextrinsiccompressionandvariousother

neuropathies(1,57,58).Itoccursmorefrequentlyin the lower extremity than in the non-weightbearing joints of the upper extremity. Long-standing poorly controlled diabetes mellitusand syringomyelia are the most common causein upper and lower extremities, respectively.Neuropathic spondyloarthropathy may affectthe spine in the settingof traumatic spinal cordinjury, amyloidosis, tabes dorsalis, congenitalinsensitivity to pain and occasionally diabetesmellitus(1,57). The disease can manifest radiologicallyas hypertrophic, atrophic or mixed form ofarthropathy or as neuropathic fractures.Hypertrophic joints reveal joint destruction,

Figure 13:Knowncaseof rheumatoid arthritiswith ricebodies.Lateral radiographof the ankle (a)revealsalobulatedsofttissueswellingonitsanterioraspect.SagittalT1andT2-weightedimages (b and c) demonstrate fluid distension of the extensor digitorum longus tendonsheath(arrows)withintacttendon.Post-gadoliniumfatsuppressedT1-weightedimage(d)reveals synovial thickeningand intense enhancementof the tendon sheath.Features areconsistentwithtenosynovitis.Numerousuniformsized,tinymiliaryT2hypointensenodulesnotedwithinthesynovialfluidaresuggestiveofricebodies.

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disorganisation and fragmentation, sclerosis,effusion,osseousdebrisandosteophyteformation.Osteophytes related to neuropathic arthropathyreveal ill-defined and roundedmargins at earlystagesandmayattainenormoussizesatlaterstagescompared to osteoarthritis. The atrophic form,which is more common than the hypertrophicform, is characterised by osseous resorption,resultinginanappearanceofsurgicalamputation(Figure 15), or licked candy stick appearance.The atrophic type may mimic septic arthritis.Joint disorganisation & large persistent bloodyjoint effusion are observed in both the forms.Osseousfragmentationanddebris,ahallmarkofneuropathic osteoarthropathy, may be confusedwith tumourmatrixonradiographs,particularlyaschondroidmineralisationofchondrosarcoma.Neuropathic fractures may occur in long bonesspontaneously or with minor trauma. They aretypically transverse in orientation andmayhealwithexuberantcallusformation(57,58).

Haemophilic arthropathy Haemophilia is associated with recurrentbleeding in joints, bones and soft tissues withconsequent synovial hyperplasia, chronicinflammatory changes, fibrosis, and siderosis ofthe synovial membrane, joint contractures andsoft tissues and intra-osseous pseudotumors

Figure15:A42-year-oldmanwithtypeIArnoldChiarimalformation,nowpresentingwithapainlessright shoulder mass. Sagittal T2-weighted image (d) of the cervical spine demonstratestonsillar herniation (arrowhead) with a benign syrinx in upper cervical and upperthoraciccord(arrows).Antero-posteriorradiographoftherightshoulderjoint(a)revealsresorption of the upper end of humerus resembling surgical amputation associatedwithjointdisorganizationandlargesofttissueswellingcontainingcalcareousdebris(arrows).Axial T1-weighted (b) and coronal fat suppressed T2-weighted (c) images confirm theradiographic findings (arrowhead = resorbed humerus) and reveal a large joint effusion(arrows).Aspirationofshoulderjointwithathickneedleshowedthickhemorrhagicaspiratewithcalcareousmaterialwhichwasnegativeformicro-organismsonstainingandcultures.Inthegivenclinicalcontext,theimagingfeaturesarecompatiblewithneuropathicjoint.

(1,27,59,60). Haemophilic arthropathy mostoftenoccursinthe1stor2nddecadeoflife(1).Anacutebleedingepisode isusuallymono-articular(frequentlyaffecting theknee,ankle,elbow,andshoulder), but the condition tends to involvedifferent joints and become poly-articular withtime. Radiographic features include jointeffusion, osteoporosis, epiphyseal overgrowth,bony erosions and cysts, joint space narrowing,intraosseous pseudotumors and secondaryosteoarthritis.Chronichaemarthrosisofthekneeischaracterisedbywideningoftheintercondylarnotch, flattening of the condylar surface orsquaring of the patella. MRI demonstratessynovial hypertrophy with characteristicintermediate to low signal intensity in all pulsesequences and blooming on gradient-echosequences, due to the magnetic susceptibilityeffect caused by hemosiderin. The differentialdiagnosesforsynoviallesionswithlowT2signalintensity have been discussed earlier in thisarticle (1,27,59,60). Unlike PVNS, which showslobulated intra-articular synovial masses withhemosiderin(Figure16)deposition,haemophilicarthropathy reveals a more linear deposition ofhemosiderin and characteristic abnormalitiesof bone shapes as described in the text.MRI isuseful for theselectionofpatientsneedingearly


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Figure16:Axialgradientechoimageofkneejointinaknowncaseofhemophiliarevealssynovial thickening with profoundsignal hypointensity (arrowheads)suggestiveofhemosiderindepositionfromrecurrentintra-articularbleeds.

Figure17:Lipohemarthrosisinapatientwithtwistingkneeinjury.Lateralradiographofthekneeshowsafat-fluidlevel(arrowheads).CoronalT1-weightedimage(b)revealsanintra-articularlateraltibialplateaufracture(arrow).SagittalfatsuppressedT2-weightedimage(c)demonstratesthreelayersshowinghematocriteffect(blackarrow)andnon-dependentfatlayer(asterisk).

treatment of haemophilic arthropathy and inmonitoring response to therapy. Prophylaxis(infusionoffactorconcentrateonaregularbasis)and synovectomy are used to prevent or delaydestructivechanges(27).

Others Cyclops lesion, or localised anteriorarthrofibrosis, is a focal fibrous tumour in theanterior joint space of the knee and is viewedas a potential complication of anterior cruciateligament reconstruction. It shows intermediateto low signal intensity with all MR imagingpulsesequences.Thecondition ismanagedwitharthroscopicresection(61). Degenerative joint disease may present asnon-specificsynovitis,ganglions,(62,63)synovialcysts,parameniscalorparalabralcystsandintra-articularloosebodies. Abnormal suprapatellar plicae may lead tocompartmentalisationofthejointanddistentionof thesuprapatellarbursamanifestingasasoft-tissuemass(64).Lipohaemarthrosisresultsfroman intra-articular fracture leading to release ofmarrowfatintothejoint.OnMRI,itisobservedas fluid-fluid levels showing non-dependent fatand dependent haemorrhage layer. The layer ofbloodmayfurthershowahaematocriteffectduetoserumseparatingfromthebloodcells(Figure17)(65).

Conclusion

A myriad of conditions may present asarticular swelling. Figure 18 summarises the

diagnostic approach in patients presenting withsuspected tumour-like swelling in and aroundjoints.Familiaritywiththedifferentialdiagnosesof masses and mass-like conditions involvingintra- and peri-articular soft tissues, alongwiththe typical imaging characteristics as describedin this article, permits a confident radiologicaldiagnosisofmanyofthesediseases.

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Figure 18:Diagnostic approach in patients presenting with suspected tumour-like swelling in andaroundjoints.

Acknowledgement

AuthorsacknowledgeDrAshishGuliaforhistechnicalsupportinorganisingthecontentsofthemanuscript.

Conflict of Interest

None.


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Funds

None.

Authors’ Contributions

Conception, design, drafting of the article,collectionandassemblyofdata:SDAnalysisandinterpretationofthedata:SD,STQCritical revision of the article for the importantintellectualcontent:SD,STQ,GB,PJFinalapprovalofthearticle:SD,STQ,GB,PJProvisionofstudymaterialsorpatient:STQ,GB,PJ

Correspondence

DrSunitaDhandaMDRadiodiagnosis(FRCR)DepartmentofDiagnosticImagingNationalUniversityHospital5LowerKentRidgeWingSingapore-119074Tel:+65-90619157Fax:+65-67797101Email:[email protected]

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