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Imaging in CranioVertebral Junction Anomalies
- 1. IMAGING IN CVJUNCTION ANOMALIES 1
- 2. ANATOMY AND EMBRYOLOGY •Bony CVJ development is divided conceptually into 2 components: • The ‘central pillar’- Dens, basiocciput, and C2 vertebral body • ‘Two ringed structures’ – surrounding central pillar – foramen magnum, exocciput, occipital condyles, opisthion and atlantal ring. • Occipital somites (somites 1-4) and first 3 cervical somites (somites 5-7) are involved. 2
- 3. • 4th occipitalsomites – undergoes resegmentation. • Caudal dense zone of 4th occipital somites + cranial loose zone of 1st cervical somite = proatlas. • Axial sclerotome of proaltas fuses with basiocciput – forms basion. • Upper part of clivus – formed by basisphenoid. • Sphenooccipital synchondrosis fuses – 12 yrs. 3
- 4. 4 • Establishment ofpolarity in somites.
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- 7. ATLAS • Ossifies from3 centres • Each half of post. arch with lateral mass –7 to 9 wk, unites at 3 –4years. • Anterior arch – appears at 1 to 2 years, unites with lateral mass at 6 –8years 7
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- 9. JOINTS • C0-C1 joint:pair of condylar synovial joint. • Attachments: • Anterior A-O membrane: anterior atlantal arch to anterio-inferior edge of FM. • It is a continuous ALL above C1. • Limits extension of A-O joint. • Posterior A-O membrane: posterior atlantal arch to posterior outer margin of FM. • Continuous as atlantoaxial ligament and ligementum nuchae. 9
- 10. JOINTS • C1-C2 joint– A complex articulation involving 3 three synovial joints. Involves: • Paired lateral atlanto-axial joint: b/w lateral masses of C1 and C2. • Median atlanto-dental joint: pivot-type of joint b/w dens and C1 anterior arch. 10
- 11. CRUCIATE LIGAMENT • Horizontaland vertical component. • Horizontal or transverse (atlantal) ligament: from tubercles of atlas, holds dens against the anterior arch. • Provides stability for axial rotation of C1 on C2 and lateral bending. • Vertical component: from posterior aspect of dens to clivus, under posterior longitudinal ligament and tentorial membrane. 11
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- 16. Craniometric measurement Anatomic landmarks Normalvalues and clinical implicatons ADI From posterior border of anterior arch of C1 to anterior surface of dens >3mm in adults and >5mm in children indicated AAD PADI From posterior surface of dens to anterior border of posterior arch of C1 <13mm indicates canal narrowing Chamberlain’s line (Modification: McGregor line) Hard palate post. plate to opisthion Dens >6 mm above – BI McRae line Basion to opisthion Odontoid tip below by >5mm. Odontoid tip lying above – BI 16
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- 20. MCGREGOR’S LINE ANDMCRAE’S LINE 20
- 21. Craniometric measurement Anatomic landmarks Normalvalues and clinical implicatons Wackenheim clivus base line Line drawn along clivus and extending into upper cervical canal This line should fall tangent to posterior aspect of odontoid Clivus canal angle The angle formed by the Wackenheim line and a line constructed along the posterior surface of the axis body and odontoid Normal is 150-180°. If <150° ventral cord compression is present. Clivus-canal angle or NTB angle or Welcher angle Formed between the nasion-tuberculum and tuberculum-basion lines Normal: 125°-143° Platybasia: >143° BI: <125° 21
- 22. WACKENHEIM CLIVUS BASELINE 22
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- 24. Craniometric measurement Anatomic landmarks Normalvalues and clinical implicatons Klaus index Distance between tip of dens and the tuberculum torcula line. Indicates height of post. fossa. Normal is 40-41mm. Decreased in BI. Boogard’s angle Angle between McRae line and clivus base line Normal is 126° ± 6. >136° - platybasia AO Joint axis angle lines drawn parallel to the atlantooccipital joints to intersect at midline This line meet typically at the center of odontoid process. Normal – 124 to 127°. Condylar hypoplasia – more obtuse. 24
- 25. KLAUS INDEX ANDBOOGARD ANGLE 25
- 26. AO JOINT AXISANGLE 26
- 27. Craniometric measurement Anatomic landmarks Normalvalues and clinical implicatons Bimastoid line Between the inferior tips of the of mastoid processes bilaterally. Normal – intersects atlanto-occipital joint Odontoid process less than 10mm above line. Digastric line Between bilateral digastric groove Normal- 10mm above atlanto-occipital joint 27
- 28. BIMASTOID LINE ANDDIGASTRIC LINE 28
- 29. TERMINOLOGY • Basilar invagination •Basilar impression • Platybasia 29
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- 31. BASILAR INVAGINATION 31 Nasion-opisthion lineof Boogard. Platybasia Short clivus • Dens moves into plane of FM. i.e dens well above McGregor line (>5mm).
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- 33. ANTERIOR FORM OFBASILAR INVAGINATION 33
- 34. ANT AND POSTFORM OF BI 34
- 35. ANT AND POSTERIORFORM OF BI 35
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- 37. CLINICALLY SIGNIFICANT CVJANOMALIES 37
- 38. ODONTOID DYSGENESIS • 4main developmental errors are: • Hyperplasia of primordium • Aplasia/hypoplasia of primordium • Disturbance of resegmentation • Failure of midline integration of primordium 38
- 39. • Complete odontoidagenesis – a/w collagenopathy syndrome • Agenesis of basal segment – stumpy pivot with floating apical segment. • Both types a/w instability • Agenesis of apical segment – MC type. • Treatment – C1-C2 fusion. 39 C1 ODONTOID AGENESIS
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- 43. OS ODONTOIDEUM • Failureof basal dental and axis body ossification centers to fuse at LS. • Non-fusion is below the level of transatlantal lig - a/w instability. • Orthotopic and dystopic (Os avis). • Radiographic features: • Smooth, well-corticated ossicle at the superior ossicle of a hypoplastic dens • around half the size of a normal dens • a/w hypertrophied and rounded anterior arch of the atlas • Posterior arch is hypoplastic 43
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- 46. OSSICULUM TERMINALE PERSISTENS •d/to Non-fusion of ossification centers apical dental segment and basal dental segment at US. • it lies above transatlantal and alar lig. attachment – instability uncommon. • Radiographic features: • Small, well-corticated ossicle at the tip of the dens • Usually in the midline • Dens is typically normal in height 46
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- 48. OS AVIS • d/toApical dental segment attachment to basion – d/to abnormal resegmentation of proatlas centrum. • A.k.a dystopic os odontoideum. • The dental pivot has a flat top but tall enough for the TAL and has no instability 48
- 49. BIFID DENS • d/toFailure of midline integration of basal dental segment. a/w: • Partition of basal dens segment upto LS and dislocated ossiculum terminale. • One half of basal dens segment – attached to C2 body, other is free floating. • Complete bifid dens - extremely rare • Dens bicornis – only tip is bicornuate. Dental pivot is normal. • a/w failure of midline integration of other somites. 49
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- 55. BASIOCCIPITAL DYSGENESIS • d/tofailure of midline integration of basioccipital primordium: Bifid clivus. • Rare entity • Bifidity can extend upto sphenoclival synchondrosis • May threaten the anchorage of tectorial membrane. • Causes A-O joint instability. • Treatment is occipito-cervical fusion. 55
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- 58. OCCIPITAL CONDYLUS TERTIUS •d/to Hyperplasia of proatlas hypochordal bow. • May form joint or psuedojoint with odontoid process or anterior atlantal arch. • a/w limited mobility at C0-C1 joint. • a/w os odontoideum. • May need resection. • D/d: Os avis • C2 dental pivot is truncated and stability of atlantodental joint may be compromised. 58
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- 61. HYPERTROPHIC OCCIPITAL CONDYLE •d/to Hyperplasia of exoccipital sclerotome. • Bilateral condylar hypertrophy – pincers-like cervicomedullary compression and early presentation • Unilateral hypertrophy – lateral distortion of the lower brainstem and slow deterioration. • Treatment: Resection of occipital condyle f/by occiput-cervical fusion. 61
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- 63. ATLAS ASSIMILATION • d/tonon-resegmentation of proatlas. • One of the MC CVJ anomalies • First mobile segment b/w skull and spine has been transferred down to C1-C2. • 3 types of fusions identified: • Zone 1 – anterior atlantal arch assimilation • Zone 2 – lateral processes assimilation • Zone 3 – posterior atlantal arch assimilation • Most of burden of movements falls on C1-C2 – develop over-stretch failure - likely to develop C1-C2 instability. • Treatment - aimed at stabilizing C2-C3 joint. 63
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- 65. ANOMALIES OF ANTERIORATLANTAL ARCH • d/to aplasia or hypoplasia of C1 hypochordal bow. • Complete aplasia – extremely rare 65
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- 70. ANOMALIES OF POSTERIORATLANTAL ARCH • d/to Aplasia or hypoplasia of lateral C1 sclerotome. • More common than anterior atlantal arch defects. • Dens anchorage to C1 by transatlantal lig is normal. • These patients are usually stable. • Rarely require fusion. 70
- 71. COMPLETE POSTERIOR C1ARCH AGENESIS 71
- 72. UNILATERAL POSTERIOR C1ARCH AGENESIS 72
- 73. OCCIPITAL CONDYLAR HYPOPLASIA •d/to hypoplasia of lateral sclerotome of proatlas. • Occipital condyles are flattened, leading to BI • Violation of the Chamberlain line and widening of the atlanto occipital joint axis angle. • Upward slanting of skull base. • The lateral masses of the atlas may be fused to the hypoplastic condyles, further accentuating the BI. • Limits or may even abolish movements at the A-O joint. 73
- 74. OCCIPITAL CONDYLAR HYPOPLASIA 74 Upwardslanting of the skull base.
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Editor's Notes
- #5 Dorsoventral differentiation of somite. A Epithelial somite shows ventromedial cells (VM) destined to form the sclerotome. B Ventromedial sclerotome cells (Scl) de-epithelize from the somite and migrate towards the ventral notochord (NC). C Sclerotomal cells further subdivide into an axial cluster (Scl-A) surrounding the notochord, and lateral paired clusters (Scl-L) flanking the perichordal axial sclerotome. Dorsolateral somite retains its epithelial pattern to become the dermomyotome (DM). D The lateral sclerotome (Scl-L) forms a triangle next to the axial sclerotome. The three sides of the triangle become anlagen for the pedicle (P), neural arch (N) and the costal process (C), respectively. The dermomyotome also subdivides into the dermatome (D) and the lateral migrating myotome (M)
- #7 Severance line The severance line appears to go through the original resegmentation fronts of the adjacent somites 4 and 5, so that the final cellular separation occurs right through the junction between the basion and the apical segment of the dens, both derived from the axial portion of the proatlas, which in turn comes from a combination of the caudal half of somite 4 and the rostral half of somite 5
- #8 Atlas ossification centers. Diagram depicts the ossification centers of the atlas..
- #9 The making of any part of the vertebral column requires the successful completion of three developmental phases: First, the mesodermal primordium has to be properly formed and, in some cases, assembled during the membranous phase; Second, the mesodermal primordium undergoes chondrification in the cartilaginous phase; and Finally, in the osseous phase, ossification takes place within the cartilaginous mold to complete the end product.
- #13 Transverse component of the cruciate ligament. Axial proton density CUBE image (A) shows the curved black structure, which represents this transverse band (white arrows). Sagittal reformat of proton density CUBE sequence (B) shows the transverse band (long white arrow) between the dens (star) and the tectorial membrane (short black arrowheads) and posterior longitudinal ligament (long black arrows)
- #14 T2W MR both. ateral margins of the sloping upper posterior margin of the dens of C2 to the lateral margins of the FM (adjacent to the occipital condyles). Limit axial rotation and contralateral flexion.
- #15 T2W image (C) showing the various secondary stabilising ligaments in relation to odontoid and CVJ. TAL = Transverse atlantal ligament, 1: Anterior atlanto-occipital membrane, 2: ALL, 3: Tectorial membrame, 4: Posterior atlantooccipital 5. lig flavum, 6. PLL.
- #17 ADI- Atlanta-dental interval, PADI, posterior Atlanta-dental interval
- #19 ADI and PADI, lateral radiograph, sagittal CT and MR T2 image.
- #20 Chamberline
- #21 Mcgregor and McRae
- #23 Weckenheim clivus base line
- #24 NTB welcher angle
- #26 Klaus index and boogard angle
- #27 AO Joint axis angle
- #29 Bimastoid line and digastric line
- #30 The term ‘ ‘ basilar invagination’ ‘ refers to a primary developmental anomaly in which the vertebral column is abnormally high and prolapsed into the skull base (2). Because the anomaly may be due to a number of causes (basiocciput hypoplasia, occipital condyle hypoplasia, various atlantooccipital assimilations), it might be best to think of basilar invagination as a radiographic finding and not a diagnosis in and of itself. Also a/w neural dysgenesis, syringomyelia and chiari The term “basilar impression’ include reserved for the secondary or acquired form of basilar invagination. It results from softening of the skull base and is uncommon, Paget disease osteomalacia Hyperparathyroidism Osteogenesis imperfecta Hurler syndrome Rickets Skull base infection Platybasia refers to flattening of the skull base, manifested by an increase in the Welcher basal angle.
- #32 Normal clival angle () measured by the NTB angle of Welcker joining the nasion (N), tuberculum (T) and basion (B). The angle should be less than 130°. Platybasia is marked by an increased NTB angle. This raises the basion and forces the foramen magnum plane (dotted line) to tilt upwards. The same upward tilt of this plane also occurs with a short clivus (normal clivus length is 4 to 4.4cm)
- #33 Severe lordotic tilting of the plane of the occipital condyle in short clivus and platybasia.. Normal clivus and opisthion are represented by dotted outlines, and orientation and plane of the occipital condyle are represented by arrow and semicircle, respectively; red for normal and black for abnormal. The fusion and chondrification of the basioccipital and the exoccipital sclerotomes occur slightly earlier than the resegmentation of the C1–C2 sclerotomes. A severely lordotic skull base angle consequently forces the emerging upper cervical sclerotomal column to bend backwards “in sympathy”, especially its centra complex that will ultimately form the dens–axis (Fig. 39). This explains why platybasia and short clivus are frequently associated with a retroflexed and lordotic dens, that, in severe cases, points sharply and wickedly backwards into the brainstem
- #34 T2 MR: Anterior form of basilar invagination caused by an exceedingly short (<1 cm) and blunted clivus (arrow) with severe lordotic tilt of the plane of the foramen magnum, leading to a “sympathetic” lordotic bend of the dental pivot resulting in a retroflexed odontoid and basilar invagination
- #35 Combined anterior–posterior form of basilar invagination. A Sagittal CT shows extreme platybasia (NTB angle=180°), short clivus (<1.5 cm) and forward folding of the clivus–axis angle of Wackenheim (80°), causing lordotic tilt of the foramen magnum plane and plane of the occipital condyles, resulting in a retroflexed dens and severe basilar invagination. Note violation of McGregor’s, Chamberlain’s and McRae’s lines by the dens. Also, extreme invagination of the opisthion (O) and high posterior C1 arch (C1).
- #36 Sagittal MR shows distortion and compression of brainstem by both the dens and the opisthion
- #37 Platybasia and short clivus (<1.5 cm; sphenoclival synchondrosis marked by arrow) causing severe basilar invagination and mild retroflexed dens. This results in a shallow posterior fossa with a Klause index (K) of less than 1.8 cm and ectopic cerebellar tonsils (chiari 1) and cervical syringomyelia
- #40 a/w spondylometaphyseal or spondyloepiphyseal dysplasia Fig: T1 MRI Agenesis of apical dental segment, with a slightly short dental pivot but a definite basal segment (pointed) and a lower dental synchondrosis (LS). Arrow points to anterior arch of C1. Note platybasia and Chiari I malformation
- #41 Lateral radiograph shows complete absence of odontoid process. Midsagittal T1 MRI of brain and cervical spine. The cervicomedullary junction is atrophic.
- #42 Complete agenesis of the dens in a 10-year-old child with spondyloepiphyseal dysplasia. a CT sagittal and coronal views show no dental pivot Although the centrum with a flat top does rise up above the “expected” level of the lower dental synchondrosis.
- #43 3-D CT reconstruction and MR show the flat top of the centrum and potential for instability
- #44 D/d: Odontoid fracture type 2 Persistent ossiculum terminale
- #45 Os odontoideum in an 8-year-old child presented with multiple cerebellar and thalamic strokes. b CT scans show multiple small infarcts of left cerebellar hemisphere and thalamus secondary to multiple vertebrobasilar emboli. Cerebral angiogram shows os odontoideum with a corrugated horn-like inferior edge (arrow) with anterior C1– C2 subluxation and stretch injury to the vertebral artery.
- #46 Coronal 2D CT through plane of os odontoideum. The ossicle has defined cortical borders. There is a gap below it and a hypoplastic dens present. i Midsagittal T2-weighted MRI of CVJ. The cervicomedullary junction is draped over the superior axis body. Note the cruciate ligament in front of the axis; below the ossicle.
- #47 D/d: Type 1 odontoid fracture.
- #48 Unstable ossiculum terminale in a 2-year-old child with intermittent quadriparesis. a Flexion (upper) and extension (lower) sagittal reconstructed CTs showing highly mobile ossiculum (O) and C1 with obvious translational subluxation.
- #51 Completely bifid dens. a Note complete lack of midline integration of basal dental segment down to lower dental synchondrosis and an unfused and forward dislocated apical dens, suggesting midline integration abnormality interferes with growth and fusion of adjacent upper dental synchondrosis.
- #52 Flexion–extension CT shows C1–C2 instability
- #53 Sagittal MR shows severe cord compression with flexion. Arrow points to small ossiculum
- #54 State of ossification of the dens of a 4-year-old child. The tip of the basal dental segment is bicornuate from bilateral secondary ossification centres. Small density above this represents early third wave of ossification within the apical dental segment. Note lower dental synchondrosis (LS) in the coronal and sagittal views
- #55 Dens bicornis in a 7-year-old child. Lower synchondrosis has closed. Dens pivot is of normal height, suggesting the bifid tip is of the apical segment
- #57 Axial CT shows the gap in the lower clivus (arrow). Right: Sagittal CT shows the odontoid process is far anterior to its usual position below the clivus. Fusion of the C2, C3 and C4 centra is also seen
- #58 CT 3-D rendering of the skull base. Left: View from the back shows widely bifid basiocciput and an oval defect (arrow) higher in the clivus. The posterior C1 arch is deficient. Right: view from the front shows the odontoid is far forward from the bifid clivus (mostly covered by the dens), and the anterior C1 arch is also bifid. Note upper clival defect (arrow). Incom post C1 arch incomplete posterior C1 arch; Incom ant C1 arch incomplete anterior C1 arch
- #60 Pre-basioccipital arch (thin arrows), a U-shaped bony valance on the ventral lip of the anterior foramen magnum rim. This results from complete preservation of the hypochordal bow of the proatlas. remains solid anchor for the TAL; instability is unlikely. Although some third condyles are short and protrude along the contour of the clivus or even curl forward away from the brainstem
- #61 Third occipital condyle or condylus tertius (thin arrow) attached to the ventral surface of the clival tip and fused to the anterior atlantal arch (thick arrow). On MRI, the condyle appears to form a synovial joint with an ossiculum terminale that is unfused to the basal dens. The third occipital condyle represents midline hyperplasia of the proatlas hypochordal bow
- #63 Unilateral hyperplasia of the occipital condyle (arrow) with cervicomedullary distortion. This represents hyperplasia of the exoccipital (lateral) sclerotome of the proatlas
- #65 C1 assimilation or occipitalization. a Assimilation of the anterior atlantal arch (zone 1 assimilation). b Assimilation of the lateral masses (zone 2 assimilation). c Posterior arch (zone 3) assimilation
- #67 Complete aplasia of C1 hypochordal bow—complete aplasia of C1 anterior arch. a CT and 3-D reconstruction shows no anterior atlantal arch or insertion tubercles for the TAL. The two anterior stunted dental hemi-os (arrow) are unfused to the C2 centrum. Posterior arch of C1 is also unfused.
- #68 Extreme C1–C2 flexion instability and severe cord compression
- #69 Severe hypoplasia of C1 hypochordal bow—small anterior C1 arch. a Match-head size anterior C1 arch (thick arrow) associated with complete agenesis of the dens (thin arrow), a result of concomitant C1 centrum aplasia.
- #70 C1–C2 instability with cord compression
- #72 Complete agenesis of posterior atlantal arch and bifid anterior atlantal arch. Normal TAL insertion tubercles (arrows). There is no C1–C2 instability
- #73 Unilateral aplasia of the right posterior arch of C1
- #75 Coronal CT scan reveals widening of the atlantooccipital joint axis angle (dotted line). The joints are extrapolated in this case, as the lateral C-i masses are fused to the hypoplastic occipital condyles and seem to abut the jugular tubercles
- #76 Condylar hypoplasia. (a) Coronal T1 MR image shows the extreme upward slope to the skull base in the medial direction (arrows) . (b) Axial CT scan obtained at the level of the ossicles demonstrates the sphenoid sinus (5), clivus (C), anterior arch of the atlas (dot), and odontoid process (0). It is markedly abnormal that all of these structures are visible on the same section.