CRANIOVERTEBRAL JUNCTION•The craniovertebral junction(CVJ) is a collective term thatrefers to the occiput, atlas, axis, and supporting ligaments.•It is a transition zone b/w a mobile cranium & relatively rigidspinal column.•It encloses the soft tissue structures of the cervico medullaryjunction (medulla, spinal cord, and lower cranial nerves).
EMBRYOLOGY & DEVELOPMENT OF THE CVJDevelopment of the cartilaginous cranium & the adjacent structures begins during theearly weeks of intrauterine life.2ndGestational week:Mesoderm cells condense in the midline to form notochordal process.3rdGestational week:-notochordal process invaginates in b/w ecto& endoderm to form notochord.-dorsal ectoderm thickens to form neural groove which folds, fuses, & becomes neuraltube.Between 3rd& 5thweek:-part of mesoderm which lies on either side of notochord (Paraxial mesoderm) givesrise to somites(Segmentation).-total 42 somitesform at 4thweek.-ventromedial portion of somite is k/a sclerotome which forms the vertebral bodies.-each sclerotome differentiates into a cranial, loosely arranged portion and a caudalcompact portion by a fissure k/a “Fissure of von Ebner”(Re-segmentation).
Each sclerotome differentiates into a cranial, loosely arranged portion ( 1) and a caudal compact portion (2).
Notochord disappears at the vertebral bodies, but persist as nucleus pulposus at disc.Out of 4 occipital sclerotomes the first 2 form basiocciput, the 3rd Jugulartubercles and the 4th (Proatlas) form parts of foramen magnum, atlas andaxis.The “pro atlas” (1) is derived from the cranial portion of the embryonic fourth occipitalsclerotome. Its principal derivatives are the occipital condyles, the dorsalcranial articular facets of the atlas, and the tip of the odontoid.The “primitive atlas”(2) is derived from the caudal portion of the fourth occipital and the cranial portionof the first cervical sclerotomes. Its principal derivatives are the neural arches andlateral masses of the atlas and the remainder of the odontoid process of the axis.The “primitive axis” (3) is derived from the caudal portion of the first cervicalsclerotome and the cranial portion of the second. Its principal derivatives arethe body and neural arch of the axis and the C2-3 cervical disk.
OSSIFICATION CENTRESOCCIPUT & BASIOCCIPUT:2 occipital squamous portions –2 centresBasiocciput(clivus) -1 centre2 Jugular tubercles –2 centres2 Occipital condyles–2 centresATLAS: ossifies from 3 centresEach half of post. Arch with lateral mass unites at 3 –4 years.Anterior arch unites with lateral mass at 6 –8 years.AXIS: ossifies from 5 primary & 2 secondary centres.2 Neural arches –2 centres appear at 7 –8 wkBody of axis –1 centre appear at 4 –5 monthsBody of dens –2 centres appear at 6 –7 months4 pieces (at birth) unite at 3 –6 yearsTip of odontoid appears at 3 –6 years, unites with the body of odontoid at 12 years.
EMBRYOLOGY & DEVELOPMENT OF THE CVJATLAS: no vertebral body & no IV disc.-major portion formed by first spinal sclerotome.-trasitional vertebra as centrum of sclerotome is separated to fuse with the axis bodyforming the odontoid process.-hypocentrum of 1st spinal sclerotome forms the anterior arch of the atlas.-neural arch of the first spinal sclerotome forms the inferior portion of the posterior archof atlasAXIS: develops from 2nd spinal sclerotome.-hypocentrum of 2nd spinal sclerotome disappears during embryogenesis.-centrum forms the body of the axis vertebra & neural arch develops into the facets &the posterior arch of the axis.-At birth odontoid base is separate from the body of axis by a cartilage which persistsuntil the age of 8, later the center gets ossified or may remain separate as Os-odontoidium.-The apical segment is not ossified until 3 years of age, at 12 years if fuses withodontoid to form normal odontoid failure leads to Os terminale..
ANATOMY OF CVJ(ARTICULAR)Upper surfaces of C1 lateralmasses are concave which fit intothe ball & socket configuration.4 synovial joints b/w atlas & axis–2 median –Pivot variety2 lateral –Plane varietyEach joint has its own capsule &synovial cavity.
ANATOMY OF CVJ(LIGAMENTOUS)ATLANTO-OCCIPITAL LIGAMENTS:A) Anterior Atlanto-occipital Membrane ----about 2 cm wideLigament is continuous caudally with the anteriorA-A ligament & through it to the ALL of the spinalcolumn.It acts as a tension band that stretches duringextension, serving as a secondary stabilizer againstthis motion.B) POSTERIOR ATLANTO-OCCIPITALMEMBRANE:A less strong ligament containing no significantelastic tissue.Ligament invests itself on either side to form acanal through which the vertebral artery,accompanying veins, & the first cranial nerve pass.C) LATERAL ATLANTO-OCCIPITALLIGAMENTS:-ascending lig which reinforce the A-O jointcapsules.
ATLANTO AXIAL LIGAMENTS:Anterior A-A ligament,Posterior A-A ligamentTransverse ligament of the atlas:-thick, strong & about 6mm in height.-Caudal crus & Rostral crus(Fasciculilongitudinales) fibres joined withtransverse ligament on its dorsal aspectto form Cruciate ligament of atlas.TAL effectively limits anteriortranslation and flexion of the atlantoaxial joint.An accessory band ventral to theascending crus attaching to the apex ofthe odontoid process is termed Gerber’sligament.
A) TECTORIAL MEMBRANE:•Dorsal to the cruciate ligament•Attached to the dorsal surface of the C3vertebra, axis body & to the body of dens.•Rostral extension of the PLL of thevertebral column.•Essential for limiting flexion.•The accessory bands of the ligamentpassing to the lateral capsule of the A-Ajoints --Arnold’s ligamentB) ALAR LIGAMENTS:•2 strong cords that attach to the dorsal lateralbody of the dens .•Extend laterally & rostrally.•Ventral & cranial to the transverse lig. allow ananterior shift of C1 from 3 to 5 mm.•Limit the head –atlas rotatory movement on theodontoid axis•Strengthen the A-O capsule.C) APICAL LIGAMENT:.No mechanical significance.AXIS –OCCIPITAL LIGAMENTS:
ANATOMY OF CVJ (MUSCLES)Muscles have only a minor role related to CVJ stabilization & do notlimit the movements of the joints.Their principal function is one of initiating & maintaining movement atthe CVJ.Neural structures related to CVJ are –Caudal portion of brainstem (Medulla)CerebellumFourth ventricleRostral part of spinal cordLower cranial & upper cervical nerves
ANATOMY OF CVJ (NEURAL)In cerebellum, only thetonsils, biventral lobules & the lowerpart of the vermis(nodule, uvula &pyramid) are related to CVJ.Biventral lobule is located above thelateral part of FM & the tonsils lieabove the posterior edge.CRANIAL NERVES :Lower four cranial N. are closelyrelated to CVJ.9th & 10th cranial N arise from themedulla in the groove b/w the inferiorolivary nucleus & the inferiorcerebellar peduncle.The accessory N is the onlycranial N that passes throughthe FM.
SPINAL NERVE ROOTS:The C1, C2, and C3 nerves, distal to the ganglion, divide into dorsal andventral rami.The first cervical nerve located just below the foramen magnum.The dorsal rami divide into medial and lateral branches that supply theskin and muscles of the posterior region of the neck..
ANATOMY OF CVJ (ARTERIAL)The major arteries related to CVJ arevertebral, postero inferior cerebellar arteries(PICA), and the meningeal branches of thevertebral, and external and internal carotidarteries.VERTEBRAL ARTERY arises from the upperposterior part of the first segment of thesubclavian artery in the neck.Each artery is divided into intradural andextradural parts.The branches arising from the vertebralartery in the region of the FM are the posteriorspinal, anterior spinal, PICA, and anterior andposterior meningeal arteries.The PICA is the largest branch of the vertebralartery
Brain stem arteries - anteriorview1. Posterior cerebral artery2. Superior cerebellar artery3. Pontine branches of thebasilar artery4. Anterior inferior cerebellarartery5. Internal auditory artery6. Vertebral artery7. Posterior inferior cerebellarartery8. Anterior spinal artery9. Basilar arteryThe tonsillo medullary PICA segment, which forms the caudal looprelated to the lower part of the tonsil, is most intimately related to theforamen magnum.
ANATOMY OF CVJ (LYMPHATICS)The lymphatic drainage of the O-A-A joints is primarily into theretropharyngeal LN & then into the deep cervical chain.These LN‟s also drain the nasopharynx & hence retrograde infection mayaffect the synovial lining of the CVJ complex with resultant neckstiffness & instability.ANATOMY OF CVJ (VENOUS)The venous structures in the region of the FM are divided into threegroups:-Extradural veins(extraspinal & intraspinal part)-Intradural(neural) veins, &-Dural venous sinuses( superior petrosal, marginal & occipital) The three groups anastomose through bridging and emissary veins
KINETIC ANATOMY OF CVJ CVJ units are unique with respect to the rest of the spine in that theydo not bear weight through disks, but rather through synovial joints linedwith hyaline cartilage, thus exhibit significantly more movement thanany other spinal level. ROTATION : when movement occurs about an axis. TRANSLATION: when movement occurs along an axis.
ATLANTO-OCCIPITALJOINTS :The C1 lateral masses contain theoccipital condyles in a cup-likefashion.Joint is biaxial havingmovements only around thetransverse & A-P axes.2 types of movement permitted areforward or backward bending & aslight lateral tilting motion to eitherside.These joints do not permit rotation.
ATLANTOAXIAL JOINTS : Consists of 2 lateral zygapophyseal & 2median odontoid joints (pivot joint). Rotation of atlas occurs around theodontoid. The superior facet of the axis is convex& the inferior facet of the atlas is eitherhorizontal or slightly convex.So the facets slide forward & backwardon each other with rotation. The A-A joints allow less flexion –extension motion than rotation. There is greater movement withextention (upto10deg ) than with flexion(upto5deg).
Total rotation of the entire cervicalspine is upto 90deg & approx ½occurs atthe A-A joint. With a certain degree of anteflexion,the tectorial membrane, cruciform &Apical dens ligaments become slack & donot check movement. Caput of dens then acts as a fulcrum,resulting in tightening of the tectorialmembrane with consequent checking ofanteflexion(checking effect)..
THE RADIOLOGIC IMAGING MODALITIES Conventional Radiography, includingstandard and special projection Computed tomography (CT) – MP &3D reconstructions Magnetic resonance imaging (MRI)
RADIOLOGY OF CVJPLAIN FILM EXAMINATION:A) LATERAL VIEW :B) ANTERO-POSTERIOR (AP)-OPEN MOUTH VIEW :Additionally detects dens anomalies & its lateral displacement.C) OBLIQUE VIEWS:Allows visualization of homolateral superior & inferior facetsas well as a small portion of the contralateral superior facetIntervertebral neural canal for the 3rdcervical nerve alsoevident
CRANIOMETRY:Craniometry of the CVJ uses a series of lines, planes& angles to define the normal anatomic relationshipsof the CVJ.These measurements can be taken on plain X rays,3D CT or on MRI.
THE CHAMBERLAIN’S LINENAME & SYNONYMS OFLINESDEFINITION NORMAL MEASUREMENT IMPLICATIONSChamberlain ‘s linePalato-occipital linePosterior pole of hardpalate to the Opisthion.Tip of the dens usuallybelow and upto 3 mmabove this line.Dens > 6mm in basilarimpression.H O
THE MCGREGOR’S LINEHLow occiputNAME & SYNONYMS OFLINESDEFINITION NORMAL MEASUREMENT IMPLICATIONSMc Gregor’s lineBasal lineMOST ACCURATEPostero-superior marginof Hard palate – mostinferior surface ofoccipital bone.Odontoid apex shouldn’tlie above.< 5mmSuperior lie of odontoidindicates basilarimpression.(>5mm)Low occiput
THE MCRAE’S LINEB OMc Rae’s lineFormen magnum lineAnterior and posteriorends of formenmagnum.(Basion and Opisthion)Inf margin of occiputshould lie at / below thisline. Tip of dens doesnot exceed this line.Perpendicular line alongodontoid intersects 1stline in its anteriorquadrant.Inf margin of occiput liessuperior – Basilar imp.If sagittal diameter< 20mm neurologicalsymptoms (+) (foramenmagnum stenosis)
CLIVUS-CANAL LINECBOC2HNNAME & SYNONYMS OFLINESDEFINITION NORMAL MEASUREMENT IMPLICATIONSWackenhie’s lineClivus canal lineDrawn along clivus intocervical canalOdontoid tip is ventraland tangential to lineOdontoid transects theline in basilar imp
BASILAR ANGLEMid sellaBNSBNNAME & SYNONYMS OFLINESDEFINITION NORMAL MEASUREMENT IMPLICATIONSBasilar angleWelcker’s / Martin’s /Spheno-BANasion – Centre of thesella – Basion.Angle 1370(123-1520)>1520 Platybasia(Base is elevated)+/- Basilar impressionModified MRI techniqueThis technique described by Koenigsbert et al yields a normal value range (95% C.I)116° - 118° for adults and 113° - 115° for children.Angle formed by :line extending across the anterior cranial fossa to the tip to the dorsum sellaeline drawn along the posterior margin of the clivus
THE BOOGARD’S LINENONAME & SYNONYMS OFLINESDEFINITION NORMAL MEASUREMENT IMPLICATIONSBoogard ‘s Line Nasion to Opisthion Basion should lie belowthis lineAltered in basilarimpression
BOOGARD’S ANGLETuberculum sellaTuberculum sellaB oNsCNAME & SYNONYMS OFLINESDEFINITION NORMAL MEASUREMENT IMPLICATIONSBoogard ‘s Angle Angle intersected by1st line between Dorsumsellae to Basion &Mc Rae’s line.119-1350Average - 1220> 1350Basillar impression
METHOD OF BULLC2ChamberlainBull ‘s angleAtlanto-palatine anglePosterior Angle betn1st line from Post tip ofhard palate to postmargin of foramenmagnum2nd line betn ant & posttubercles of atlasPost angle <130 If odontoid is tiltedposteriorly or in case ofchange of atlas positionThe angle > 130
RANAWAT METHODC2C1Ranawat method Line joining center of theanterior arch of C1 topost ring & another linealong the axis of theodontoid from the centreof the pedicle of C2 to 1stlineNormal distance betweenC-1 and C-2 inMen averages 17 mm( 2 mm SD)Women, 15 mm( 2 mm SD).A decrease in thisdistance indicatescephalad migration ofC-2.C2C1C2C1PEDICLE
SCHMIDT – FISCHER ANGLE(ATLANTO-OCCIPITAL JT AXIS ANGLE)OC2AA JTAO JTC1 C1NAME & SYNONYMS OFLINESDEFINITION NORMAL MEASUREMENT IMPLICATIONSSchmidt – FischerAngleAngle of axis of Atlanto-Occipital joint125 +/- 2 degrees Angle is wider incondylar hypoplasia
CRANIO-VERTEBRAL ANGLEaxCNAME & SYNONYMS OFLINESDEFINITION NORMAL MEASUREMENT IMPLICATIONSCranio vertebral angle Between clivus line andpost axial lineFlexion – 1500Extension - 1800<1500 Platybasiacord compressionBasilar impression
•BDI less than 8.5 mm comparedwith 12 mm on data from plainradiographs.• The Powers ratio demonstrated nosignificant difference comparedwith data obtained by plainradiographs.•An ADI less than 2 mm, comparedwith 3 mm previously accepted.•The AOI demonstrated 95% of thepopulation ranged between 0.5 mmand 1.4 mm.Midsagittal MDCT image of thecraniocervical junction demonstratesthe BDI as the distance from the mostinferior portion of the basion to theclosest point of the superior aspect ofthe dens.MDCT VS PLAIN RADIOGRAPHYIN CRANIOMETRY…..
Midsagittal MDCT image of the craniocervicaljunction demonstrates the Powers ratio, which iscalculated by dividing the distance betweenthe tip of the basion to the spinolaminar lineby the distance from the tip of the opisthionto the midpoint of the posterior aspect of theanterior arch of C1
MDCT image of the craniocervical junctiondemonstrates the ADI, which is calculatedby drawing a line from the posterior aspectof the anterior arch of C1 to the mostanterior aspect of the dens at the midpointof the thickness of the arch incraniocaudal dimension
Sagittal MDCT image of the craniocervicaljunction demonstrates the AOI, which iscalculated by drawing a line perpendicularto the articular surfaces of the occipitalcondyle and the lateral mass of C1. Thisline is drawn at the center of thearticulation by correlating the sagittal andcoronal images.
(NORMAL VARIANTS & ANOMALIES)THE OCCIPUT : The basiocciput forms the lower portion of the clivus. The upper portion of the clivusis formed by the basisphenoid, separated from thebasiocciput by the sphenooccipital synchondrosis. The age at which this synchondrosis fuses, ranges from “after the twelvth year”to14-16 years for girls and 16-18.5 years for boys. Most occipital anomalies are associated with decreased skull base height andbasilar invagination.CondylusTertius: When the hypochordal bow of the fourth occipital sclerotome(proatlas) persists orwhen the proatlas fails to integrate, an ossified remnant may be present at the distal endof the clivus, called the condylus tertius or third occipital condyle. This third condyle may form a joint or pseudojoint with the odontoid process orwith the anterior arch of the atlas and may lead to limitation in the range of motion ofthe CVJ. There is an increased prevalence of osodontoideum associated with this abnormality
The Mach effect of theoverlying anterior arch of theatlas may be mistaken for afracture of the apical region ofthe odontoid on the openmouth view.Pseudo fracture of the odontoidThe Mach effect of the medial aspects ofthe overlying incisors simulates averticaldefect in the odontoid on the open mouthview. A bicornuate odontoid should beconsidered.
The characteristic "V" shaped cleft in thesuperior aspect of the odontoid and the"diamond" shaped distal ossification centreof pro atlas origin, are seen in the openmouth view. This is a normal finding inadolescent children.Bicornuate odontoid…….
The radiolucent band separating the base of theodontoid from the body of the axis in thelateral projection is a normal finding in infants.Sub dental synchondrosis……
The irregular fragments located inferior tothe Anterior arch of the atlas may bemistaken for fracture fragments . The clearcortical margins and characteristic locationhelp to differentiate this variant from afracture.Accessory ossification centre for the anterior arch ofthe atlas……
CondylarHypoplasia:•In condylar hypoplasia, theoccipital condyles areunderdeveloped•Have a flattenedappearance, leading to BIBasiocciput Hypoplasia:•It results in shortening of the clivusand violation of the Chamberlainline•Virtually always associated withbasilar invagination.•The Wackenheim clivus baseline isusually normal,• Clivus-canal angle is typicallydecreased• Bow-string deformity of thecervicomedullary junction.
Sagittal T1 weighted (600/20) MRI showsdeformity of the pons and medulla due tobasilar impression. Note basiocciputhypoplasia
Atlantooccipital Assimilation / Occipitalization ofAtlas:•The failure of segmentation between the skull andfirst cervical vertebra results in assimilation of theatlas.•The assimilation may be complete or partial.•It invariably results in basilar invagination.•Wackenheim clivus baseline may be normal, butthe clivus-canal angle may be decreased.TOPOGRAPHIC FORMS (WACKENHEIM):•Type I: Occipitalization(generally subtotal)associated with BI.•Type II: Occipitalization(generally subtotal)associated with BI & fusion of axis & C3.•Type III: Total or subtotal occipitalization with BI& maldevelopment of the transverse ligament.
ATLAS : Most atlas anomalies, when isolated, produce no abnormal CVJrelationships and are not associated with basilar invagination. The vast majority of anomalies consist of various arch clefts,aplasias, and hypoplasias. Arch anomalies are frequently mistaken for fractures in theevaluation of plain radiographs of patients with a history of cervicalspine trauma.
PONTICULUS POSTICUS / KIMMERLE’SDEFORMITY : It is a bony ridge projecting posteriorlyfrom the articular edge of the atlas superiorarticular facet. The bony projection unite with theadjacent neural arch of the atlas to produce an“ARCUATE CANAL”through which thevertebral artery passes. This is due to ossification of a portion ofthe oblique A-O ligament.Posterior Arch Anomalies (MC atlasanomaly) : Total or partial aplasia of the posterioratlas arch is rare. Although absence of the posterior arch,when isolated, is usually asymptomatic, butmay be associated with anterior atlantoaxialsubluxation.Posterior arch hemiplasia
Split Atlas :•In anterior arch rachischisis, theanterior arch appears fat orplump and rounded inconfiguration, appearing to„„overlap‟„ the odontoid process.•The arch may have unsharp,duplicated anterior margins.
Persistent OssiculumTerminale: Also called Bergman ossicle, results fromfailure of fusion of the terminal ossicle to theremainder of the odontoid process. The fusion typically is accomplished by 12years of age. Bergman ossicle may be confused with atype 1 odontoid fracture (avulsion of theterminal ossicle), and absolute differentiationbetween the two diagnoses may be difficult.OdontoidAplasia:Total aplasia of the odontoid process is extremelyrare.A true aplasiais associated with an excavationdefect into the body of axis.CONGENITAL ODONTOID ANOMALIES OR DYSPLASIAS
OS ODONTOIDEUM•an independent osseous structure lying cephalad to the axis body in the location ofthe odontoid process.•The anterior arch of the atlas is rounded and hypertrophic but the posterior arch ishypoplastic.•Cruciate ligament incompetence and A-A instability are common•The margins of the axis body, the os, and anterior arch are all well corticated.•Odontoid fracture : flattened, sharp, uncorticated margin to the upper axis body.Types –Orthotopic & Dystopic.Instability is more common with dystopic type.
PLATYBASIABASILAR IMPRESSIONBASILAR INVAGINATIONThese terms are not synonymous.
PLATYBASIA/Martin’s anamolyFlattening of angle between the clivus andthe body of the sphenoidC/FPRIMARY- Isolated or in conjunction with otherdysplasias like Achondroplasia,Osteogenesis imperfectaSECONDARY - Paget‟s disease / bonesoftening / degenerative diseaseBasilar angle > 152 (N=123-1520)Craniovertebral = clivus-canal anglebecomes acute (<150 )MC associated changes - Basilarinvagination, anomalies ofC1(occipitalisation)block vertebra,Klippel-Feil syndrome.
•BASILAR INVAGINATION•Floor of the skull is indented by the uppercervical spine, & hence the tip of odontoidis more cephalad protruding into the FM.•Two types of basilar invagination:primary invagination, and secondary•Primary invagination can be associatedwith occipito atlantal fusion, hypoplasia ofthe atlas, a bifid posterior arch of the atlas,odontoid anomalies.•BI is associated with high incidence ofvertebral artery anomalies.Chamberlain‟s line- tip of dens is >6mm above this lineMc Gregor‟s line- tip of dens is > 5mm above this lineMc Rae‟s line- tip of dens is above this lineBoogard‟s line- basion is above this lineHeight index of Klaus < 30mm
.Topographic types of BI : Anterior BI : hypoplasiaof basilar process of the occipital bone. BI of the occipital condyles(Paramedian BI)Condylar hypoplasia BI in the lateral condylar area. Posterior BI: posterior margin of the FM is invaginated. Unilateral BI. GeneralisedBIusually occur in 2nd or 3rd decade.
BASILAR IMPRESSION(SECONDARY BASILARINVAGINATION•Basilar impression refers to secondary oracquired forms of BI• Due to softening of the bone• Seen in conditions such as rickets,hyperparathyroidism, osteogenesisimperfecta, Paget disease, neurofibromatosis,skeletal dysplasias, and RA & infectionproducing bone destruction.
KLIPPEL FEIL SYNDROMEDescribed first by Klippel and Feilin 1912.Etiology is unknown.Due to failure of the normal segmentation of cervical somites during the third andeighth weeks of gestation.Classic triad of low posterior hair line, short neck and limited neck ROM found inless than 50% of casesThe most consistent finding is limitation of neck motion.
Achondroplasia:Genetically dominant disorder characterized by inhibition ofendochondral bone formation.The base of the skull is affected but the membraneous convexity skullbone grows normally.This differential bone growth results in large calvarium on a small base.A small FM with hypertrophic bone & a posterior dural shelf results incompression of neural structures..
CRANIOVERTEBRAL JUNCTION ANOMALIES IN DOWN SYNDROME First described in 1965 by Tishler& Martel. Characterized by increased ligamentous laxityand abnormal joint and bony anatomy, whichpredispose to instability. The incidence of bony anomalies involving theoccipital condyle, C1 ring, and odontoidis alsoincreased in Down syndrome.
CHIARI MALFORMATION The Chiari malformations are a group of hindbrain herniationsyndromes initially described by Austrian pathologist Hans Chiari in1891.
ARNOLD-CHIARIMALFORMATION IPresent in adulthood ="cerebellartonsillar ectopia"Herniation of cerebellar tonsils > 5mmbelow a line connecting Basion withOpisthion (= foramen magnum)Causes:• small posterior fossa,•cerebellar overgrowth,•disproportionate CSF absorptionAssociated with:1. Syringohydromyelia (30-56%)2. Hydrocephalus (25-44%)3. Malformation of skull baseNECT:Effaced Posterior Fossa cisterns"Crowded" Foramen MagnumLateral/3rd ventricles usually normal
Look for absent cisterna magna, posteriorly angled odontoid withcompressed brainstem, short posterior arch C1, short supraocciput,syrinx
ARNOLD-CHIARIMALFORMATION IIDes:Most common and serious complex ofanomaliesHALLMARK is dysgenesis ofhindbrain with(1)caudally displaced 4th ventricle(2)caudally displaced brainstem(3)tonsillar + vermian herniation throughforamen magnumAssociated with:(a)spinal anomalies(1)lumbar myelomeningocele(2)syringohydromyelia3)dysgenesis of corpus callosumRadiographyLucken shadel -Craniolacunia = Lacunar Skull= mesenchymal dysplasia of calvarialossificationAbsent / Hypoplastic posterior arch of C1MyelographyTethered cordNECTSmall posterior fossaLarge, funnel-shaped foramen magnum"Scalloped" petrous pyramid,"notched" clivusAbsent falx cerebelliBest diagnostic cluePresence of MyelomeningoceleSmall posterior fossaElongated, "straw-like" 4th ventricle"Cascade" of tissue herniates throughforamen magnum behind upper cervical cord• Vermis (nodulus)• Choroid plexus of 4th V• Medullary "spur"
ARNOLD-CHIARIMALFORMATION III• High cervical / occipitalmeningoencephalocele + intracranialChiari 2malformationNECTo Occipital squamo defectPosterior spina bifida at the P1–P2 levelo Bony features of Chiari 2Small posterior cranial fossa, scallopedclivus, lacunar skullMR FindingsTIWISac contents• Meninges, cerebellum, brain stem• Cisterns, 4th ventricle, dural sinuseso HydrocephalusT2WI: Tissues in sac may be bright (gliosis)MRV: Veins in cephalocele
ARNOLD-CHIARI MALFORMATION IVExtremely rare anomaly probably erroneously included as type of Chiari malformationAgenesis of cerebellumHypoplasia of ponsSmall + Funnel-shaped posterior fossa
Atlanto-Axial Instability•A: Rotational–Around the dens•B: Translational–Translation between C1–C2, where transverse lig is disrupted•C: Distraction:–Indicating craniocervical dissociation
Non-traumatic conditions associated with increase in the atlanto axialdistance: Down syndrome Due to laxity of the transverse ligament Grisel syndrome Atlantoaxial subluxation associated with inflammation of adjacentsoft tissues of the neck Rheumatoid arthritis From laxity of the ligaments and destruction of the articular cartilage Osteogenesis imperfecta Neurofibromatosis Morquio syndrome Secondary to odontoid hypoplasia or aplasia Other arthridities (Psoriasis,Lupus)
On the open mouth odontoid view, the combined spread of the lateralmasses of C1 greater than 6.9 mm would indicate rupture of thetransverse ligament.An atlantoaxial distance greater than 4-5 mm by lateral radiographs,is indicative of AAI.Posterior atlanto dental interval (PADI):Normal range is 19 –32 mm in male & 19 –30mm in females.Below 19mm, neurological manifestations occur.
Rotatory displacement(Fielding and Hawkinsclassification): Type I is simple rotatorydisplacement with an intacttransverse ligament. Type II injuries involveanterior displacement of C1on C2 of 3-5 mm with onelateral mass serving as a pivotpoint and a deficiency of thetransverse ligament. Type III injuries involvegreater than 5 mm of anteriordisplacement. Type IV injuries involvethe posterior displacement ofC1 on C2.
TUBERCULOUS AADCompression of CMJ could be due to granulation tissue, cold abscess orbony instability & displacement.Ligaments are extensively infiltrated by the disease process & give way.Hyperaemic decalcification occurs.Radiological findings in 3 stages–Stage I: Retropharyngeal abscess with ligamentous laxity +, bonyarchitecture of C1-C2 preserved.Stage II: Ligamentous disruption with AAD, minimal bone destruction& retropharyngeal mass +Stage III: marked destruction of bone, complete obliteration of anteriorarch of C1 & complete loss of odontoid process, marked AAD & O-Ainstability.
RHEUMATOID ARTHRITIS & CVJ First described by Garrodin 1890. 20% of the patients with RA have AAD. AAD is due to loss of tensile strength & stretching of TL due to destructiveinflammatory changes as well as secondary degenerative changes in tissues fromvasculitis. Odontoid process –osteoporosis, angulation/ #. BI occurs secondary to loss of bone in lateral mass of the atlas with resultant rostralmigration of axis vertebra. The lateral mass of atlas may # with lateral displacement of bone fragment. Later on erosion of occipital condyles occur..A hook like appearance of the odontoid processoccurs seconadary to the cruciate lig pannuseroding into the odontoid process
TRAUMATIC LESIONS OF CVJOCCIPITAL CONDYLE #:MC clinical features are LOC or cranial nervedamage.Classification (Anderson & Montesano):Type I & II are stable injuries while type III ispotentially unstable.Type I (comminuted fracture with minimal or no displacementType II (basilar skull fracture extending to the occipital condyle)Type III (fracture with a fragment displaced medially from theinferomedial aspect into the foramen magnum)
OCCIPITO-ATLANTAL INSTABILITY:Traumatic / non traumaticTraumatic usually fatal, 8% incidence in RTA.Traynelis classification:
# OF ATLAS: Posterior arch #: 2/3rdof all #,occur at the junction of posterior arch & lateral mass (hyperextensioninjury).Anterior arch #: rareJefferson s # : burst # of atlas,1st described by Geoffrey jefferson in 1920.
HANGMAN’S # ( TRAUMATIC SPONDYLOLISTHESIS OF AXIS ):“Judicial Hanging”- submental knots causes # dislocation of neural archof axis.I:Bilateral pars fractures with translation <3 mm and no angulation; most commonIA:CT: extension of one fracture line into the body and often through the foramentransversarium(vertebral artery injury may occur)
II :C2-3 disc and PLL are disrupted, resulting in translation >3 mm and markedangulation.IIA: Fracture line is more oblique than verticalIII:A combination of pars fracture with dislocation of the C2-3 facetjoints
ODONTOID #:Constitute about 7 –14 % of cervical spine #.Flexion is the MC mechanism of injury causinganterior displacement of C1 on C2.
NEOPLASMS OF CVJ Unusual Metastatic malignancies, such ascarcinoma of the breast, lung,prostate, kidney and thyroid inadults; and neuroblastoma , Ewing‟stumor, leukemia, hepatoma andretinoblastoma in children, are mostcommon. Primary malignancies involvingthe cranio cervical junction arerare(multiple myeloma). Benign tumors are very rare.
Craniovertebral junction (CVJ)abnormalities involve the osseousstructures and the contained nervoussystem. -Advances in Digital radiography ,computed tomography and magneticresonance imaging (MRI) haveprovided better insight into thenormal anatomy and pathology of thiscomplex area.
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