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CASE REPORT

Calcification of the Alar Ligament Mimics Fractureof the Craniovertebral Junction (CVJ): An Incidental Finding

from Computerised Tomographyof the Cervical Spine Following Trauma

Siti Kamariah Che MohaMed, Azian abd. aziz

Department of Radiology, Kulliyyah of Medicine, International Islamic University Malaysia, 25710 Kuantan, Pahang,Malaysia

Submitted: 2 Jul 2009 Accepted: 25 Aug 2009

Abstract

When performing a radiological assessment for a trauma case with associated head injury,afragmentofdensetissuedetectednearthecraniovertebral junctionwouldrapidlybeassessedasa fractured bone fragment.However, if further imaging and evaluation of the cervical spinewithcomputerised tomography (CT) did not demonstrate an obvious fracture, then the possibility ofligamentcalcificationwouldbeconsidered.Wepresentacaseinvolvingapreviouslyhealthy44-year-oldmanwhowasadmittedfollowingasevereheadinjuryfromaroadtrafficaccident.CTscansofthehead showedmultiple intracranial haemorrhages,while scans of the cervical spine revealed asmall,well-defined,ovoidcalcification in therightalar ligament.Thiswas initially thought tobeafracturefragment.Althoughsuchcalcificationisuncommon,accidentandemergencyphysiciansandradiologistsmayfindthisusefulasadifferentialdiagnosisinpatientspresentingwithneckpainortraumaticheadinjury.

Keywords:cervical spine, calcification, computerised tomography, injury, medical sciences

Introduction

Calcification in the region of the uppercervical spine is rare, although a few cases havebeenreportedinvolvingcalcificationofthealarortransverse ligament of the atlas.The calcificationusuallydevelopsasaresultoftraumaticinjuryorinflammatorydiseaseandisespeciallyprominentin the elderly (1–3). Inpatientswith ahistory oftrauma, alar ligament calcification can mimic afracture of the craniovertebral junction (CVJ).As anuncommonnormal variant, it is importantfor accident and emergency physicians; andradiologists, to be able to distinguish suchcalcification from a fracture. We present a headinjury case where the calcification was onlyincidentally detected andwas initially thought tobeafracturefragment.

Case Report

A 44-year-old man who was involved ina road traffic accident (RTA) was admitted fordeterioration in his level of consciousness. Anurgentcranialcomputerisedtomography(CT)scanshowed a large right temporoparietal extraduralhaemorrhage(EDH),alefttemporalhemorrhagiccontusionandmultiple skull vault fractures.Dueto the severity of the head injuries, a CT scan ofthe cervical spine was also performed. A small,well-definedregionofcalcifiedtissuewasdetectedbetween the odontoid tip and the right occipitalcondyle (Figure 1). The pre-vertebral soft tissueat the upper cervical spine was not thickened(measuringabout4.6mmattheC2levelonthemidsagittalmultiplanar reformat [MPR]). There wasno indicationofoccipito-atlantodissociation (thebasion-dentalintervalmeasured4.3mm,whichiswithintheacceptednormalrange)(Figure2).Therestofthecervicalspineseemedundisrupted.

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In view of the RTA and severity of thehead injuries, a fracture at the CVJ was initiallysuspected. However the origin of the fracturedfragmentcouldnotbedetermined.OncomparisonwithsagittalandcoronalMPRimages(Figure3a&3b), awell corticated structure (measuring about6.5x3.8x4.0mm)wasidentifiedbetweentherightoccipitalcondyleandodontoidtip.Thisindicatedthat the anomalywas a calcified structure ratherthan a fragment of bone. The adjacent occipitalcondyle, odontoidprocess andneural archof theatlas showed smooth and well defined outlines.Thesofttissuewindow(Figure4aand4b)showedthecalcificationwaswithintherightalarligament.Unfortunately, due to the severity of the headinjuries,anddespiteevacuationoftheintracranialhaemorrhages, the patient succumbed ten dayslater.

Discussion

Thealar ligamentsoriginatebilaterally fromtheodontoidprocessandruncephaladandlaterallytoreachthemedialaspectoftheoccipitalcondyle.They are strong, rounded structures that play animportantroleinstabilisingtheheadduringrotarymotionof theCVJ.These ligamentscanbeeasilystudiedusinghigh-resolutionmagneticresonanceimaging(MRI)thatincludesaprotonattenuation-weighted sequence. The orientation of the alarligaments is highly variable and asymmetry iscommoninasymptomaticindividuals(3,4). Calcificationinthealarligamentisveryrare.It usually develops with increasing prevalenceafter the age of 40 and tends to occur followingminortraumaorasaconsequenceofinflammatorydisease (1–3). In our case, the calcification wasobservedintherightalarligament,whichissimilartothefindingsofSimandPark(1).TheydetectedanodularcalcificationintheperiodontoidareaontheinitialaxialCTscanperformedontheirpatientfollowing a severe head injury. They had alsoconsidered the possibility of a fracture involvingtheodontoidprocess(typeIfracture),theoccipitalcondyle (type III fracture) or the neural arch oftheatlasattheCVJ.MPR,MRIanda3D-CTscanof the cervical spine were performed for furtherevaluationoftheanatomyofthecalcifiedstructure.Serial,open-mouthviewsanddynamicradiographsof the cervical spine demonstrated a stablecervical spine and a persistent, constant cross-sectioncalcification.Onthebasisof thisseriesofexaminations, they concluded that the nodularcalcification occurred in the right alar ligamentandwasunrelatedtotraumaorinflammationand,therefore,wasanincidentalfinding(1).

Figure 1: Axial CT scan of the cervical spineshowingasmall,well-defined,high-densityregionlocated between the odontoid tip and the rightoccipitalcondyle

Figure 2: CT scan of the cervical spine (midsagittal MPR) showing the basion-dens interval,whichmeasuresabout4.3mm

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CASE REPORT - Alar ligament calcification on CT

BA

Figure3: MPRimages(bonewindow)fromcoronal(A)andsagittal(B)CTscansdepictawell-defined,calcifiedstructurelocatedbetweentherightoccipitalcondyleandtipoftheodontoidprocess.Aslightatlanto-occipitalsubluxationcanbeseen.Therestofbonystructuresatthecraniovertebraljunctionarenormal.

Figure 4: MPR images (soft tissue window) from coronal (A) and sagittal (B)CTscansshowcalcificationalongtherightalarligament.Thereisnoevidenceofsurroundingsofttissueinjury.

BA

Kobayashietal.(2)alsoreportedcalcificationof the alar and transverse ligaments of theodontoidprocess in twopatientspresentingneckpain.Bothpatientshadpharyngodyniaandpriornuchal pain without previous history of trauma,and their symptoms had improved graduallywithananti-inflammatorydrugtherapyandneckimmobilisation. CT scans revealed a nodularcalcificationinonepatientandapoorlydelineatedcalcified lesion surrounding theodontoidprocessintheotherpatient.SerialCTscansdemonstratedthat the calcifications shrank and disappeared

withtime.Theauthorsassumedthatthepatients’symptoms could be related to an inflammatoryreaction induced by deposition of calcium sincesecondary arthritis was not observed, and thesymptomssubsidedasthelesionsdecreasedinsize(2). Inourcase,acervicalCTscan,performedtoassessheadinjury,revealedasmall,well-defined,ovoidofhigh-densitytissueintherightperiodontoidareaalongthecourseofthealarligament.Initially,we also considered the possibility of it being abone fragment, but comparison with the MPR

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imageswashelpfulinrulingthisout.ThecalcifiedfragmentwaswellcorticatedandthesurroundingbonesoftheCVJwerewelldefined.Therewasnoconvincingevidencetoshowthatthetinyfragmentoriginated from any of the bones of theCVJ.Nocervicalfracturewasidentified.Furthermore,therewasnoevidenceofsofttissueinjuryorindicationsofinflammationorarthriticchangesaccompanyingthecalcification.Inviewofthis,weconcludedthattherewasacalcificationintherightalarligamentthatwasunrelatedtothecurrenttrauma(makingitanincidentalfinding).Unfortunately,thepatient’sconditions worsened and we were not able toperformotherimagingsuchasMRI. From our extensive literature review, therearefewcasereportsoffocalornodularcalcificationof the alar ligament; only those reported by SimandPark(1)andKobayashietal.(2)werefound.A condition called crowned dens syndrome,describing neck pain due to calcificationssurroundingtheodontoidprocess,haspreviouslybeen reported in conjunction with calciumhydroxyapatite (HA) and calcium pyrophosphatedehydrate (CPPD) crystal deposition diseases. InCTscans, thecalcifications in these instancesareseentosurroundthetopandsidesoftheodontoidprocess in a crown or halo-like distribution andcommonlyaffectthetransverseligament(5,6).Inour case, the calcification was focal and nodularand lay along the anatomical location of the alarligament. In conclusion, calcification of the alarligament should be considered as a differentialdiagnosis in a traumatic craniovertebral injury,and this is especially true when the origin of afractureisnotclearly identified.Properdiagnosisis important because the treatment, which isbeyond the scope of this paper, differs fromfracture treatment and prevents unnecessary,prolonged, external immobilisation of the neck.Havingsaidthis,fractureofodontoidprocess(typeI) and the occipital condyle (type III) should becarefullyassessedandexcludedifabonyfragmentisdetected,particularlyinofthecaseoftrauma.

Author’s contributions

Conceptionanddesign,analysisandinterpretationofdata:SKCM,AAADatacollection,draftingofthearticle,provisionofstudymaterialsandpatients:SKCMCriticalrevision,andfinalapprovalofthearticle:AAA

Correspondence

DrAzianAbd.AzizMD(USM)MMed(Radiology)DepartmentofRadiology,KulliyyahofMedicineInternationalIslamicUniversityMalaysiaP.O.Box14125710KuantanPahang,MalaysiaTel:+609-5716408Fax:+609-5146090Email:drazianaziz@gmail.com

References

1. Sim KB, Park JK. A nodular calcification of the alarligament simulating a fracture in the craniovertebraljunction.AJNR Am J Neuroradiol.2006;27(9):1962–1963.

2. Kobayashi Y, Mochida J, Saito I, Matui S, Toh E.Calcificationof thealar ligamentof the cervical spine:imaging findings and clinical course. Skeletal Radiol.2001;30(5):295–297.

3. Krakenes J, Kaale BR, Rorvik J, Gilhus NE. MRIassessment of normal ligamentous structures inthe craniovertebral junction. Neuroradiology. 2001;43(12):1089–1097.

4. Pfirrmann CW, Binkert CA, Zanetti M, Boos N,Hodler J. MR morphology of alar ligaments andoccipitoatlantoaxial joints: study in 50 asymptomaticsubjects.Radiology.2001;218(1):133–137.

5. Sato T, Hagiwara K, Sasaki M, Matsuno H, AkiyamaO. Crowned dens syndrome. Internal Med. 2005;44(2):160.

6. Wu DW, Reginato AJ, Torriani M, Robinson DR,ReginatoAM.TheCrownedDensSyndromeasaCauseofNeckPain:ReportofTwoNewCasesandReviewoftheliterature.Arthritis Rheum.2005;53(1):133–137.