Imaging Cervico-vertebral junction: AAD with BI .pptx

Imaging Cervico-vertebral junction: AAD with BI .pptx

1. Dr. Shahnawaz Alam MCh -Neurosurgery, Final year I m aging of Cranio-vertebral junction : AAD with BI

2. Craniovertebral junction The craniovertebral junction (CVJ) anatomically denotes the occiput, the first (atlas) and second cervical (axis) vertebral segments, their articulations and connecting ligaments. The occiput which surrounds the foramen magnum consists of three parts . The squamosal portion ( supraocciput ) situated in the dorsal aspect of the foramen magnum, The basiocciput or clival portion located anterior to the foramen magnum, The condylar part ( exo -occiput) that joins the clival parts and the squamosal.

3. Atlas and Axis

4. LIGAMENTS OF CVJ Principal stabilizing ligaments : Transverse atlantal ligament; Alar ligaments Eight main ligaments support the CVJ: tectorial membrane, alar ligaments, the cruciate ligament, the apical ligament, capsular joints, accessory atlanto -axial ligament; and the anterior and posterior atlanto -occipital membranes ( Debernardi et al., 2011).

5. Craniometric lines and angles Basilar angle McGregor's line Chamberlain's line MacRae's line Height index of klaus Boogard's line and angle Atlantodental interspace Method of Bull Wachenhiem line Fischgold digastric line Schmidt Fischer angle

6. Basilar Angle Welcker’s basilar angle/ Martin’s basilar angle/ sphenobasilar angle Definition : Three points are located and joined together by two lines; the subsequent angle is measured. Normal measurements : The average normal angle subtended by these two lines is 137°, with a normal variation of 123–152°

7. Chamberlain’s line/ Palato-occipital line Landmarks : A line is constructed from the posterior margin of the hard palate to the posterior aspect of the foramen magnum. The relationship of this line to the tip of the odontoid process is then assessed. Normal Measurements : In the majority of patients the tip of the odontoid process should not project above this line; however, a normal variation of 3 mm above this line may occur. A measurement of ≥7 mm is definitely abnormal .

8. McGregor’s line/ Basal line Definition : A line is drawn from the posterosuperior margin of the hard palate to the most inferior surface of the occipital bone. The relationship of the odontoid apex to this line is then examined. Normal Measurements : the odontoid apex should not lie above this line. Significance : An abnormal superior position of the odontoid indicates a basilar impression.

9. Macrae’s line/ Foramen magnum line Two assessments are then made in relation to this line: (a) the occipital bone and (b) the odontoid process. Normal Measurements : The inferior margin of the occipital bone should lie at or below this line. In addition, a perpendicular line drawn through the odontoid apex should intersect this line in its anterior quarter.

10. Significance : If the inferior margin of the occipital bone lies above this line, then basilar impression is present. If the odontoid apex does not lie in the ventral quarter of this line, a dislocation of the atlanto-occipital joint or a fracture or dysplasia of the dens may be present. When effective sagittal diameter is <20 mm, neurological symptoms occur ( Foramen magnum stenosis ).

11. Height index of klaus Definition : A line is drawn from the tuberculum sellae to the internal occipital protuberance. The vertical distance between this line and the apex of the odontoid is measured Normal Measurements : 40-41mm Significance : < 30 mm indicates basilar impression. Values between 30 and 36 mm reflect a tendency toward basilar impression

12. Boogard’s line and angle Boogard’s line : A line is drawn connecting the nasion to the opisthion. Boogard’s angle : (a) A line is drawn between the basion and the opisthion (Macrae’s line). (b) A second line is drawn from the dorsum sellae to the basion along the plane of the clivus. (c) The angle between these two lines is measure Normal Measurements :- Boogard’s line : The basion should lie below this line. Boogard’s angle : 119-135° Significance : Both measurements will be altered in basilar impression—the basion will be above Boogard’s line, and the angle will be > 135°.

13. Atlanto -dental interspace/ Atlas-odontoid space/ Predental interspace/ Atlas dens interval Definition : The distance measured is between the posterior margin of the anterior tubercle and the anterior surface of the odontoid. Special Considerations : Flexion is the optimum view for assessing the interspace because in this position the most stress is placed on the transverse ligament of the atlas.

14. Normal Measurements :- Significance : A decreased space is to be expected with advancing age because of degenerative joint disease of the Atlanto -dental joint . An abnormally widened space with a reduction in the neural canal size is seen in trauma, Occipitalization , Down’s syndrome, pharyngeal infections (Grisel’s disease), and inflammatory arthropathies. AGE MINIMUM MAXIMUM ADULTS 1 3 CHILDREN 1 5

15. Method of Bull/ Atlantopalatine angle Definition : The first line is drawn from the posterior aspect of the hard palate to the posterior margin of the foramen magnum (Chamberlain’s line). The second line is drawn through the mid-points of the anterior and posterior tubercles of the atlas (atlas plane line). The angle formed posteriorly is then measured. Normal Measurements . The posterior angle formed by these two lines should be 13°. Significance : The angle will increase if the odontoid is tilted posteriorly because of congenital malformation or fracture displacement.

16. Wackenheim’s line (Clivus canal line) Definition : Line drawn along Clivus into cervical canal. Normal Measurements : Odontoid tip is ventral and tangential to this line. Significance : Odontoid process transects the line in basilar invagination.

17. Fishgold digastric line ( Biventer line) Definition : Joins the fossae for digastric muscles on undersurface of skull (Just medial to mastoid process) Normal : Dens tip should not project above this line. Central axis of dens should be perpendicular to the line. Significance : Odontoid tip should not project above this line.

18. Schmidt-Fischer angle Definition : Angle of axes of atlanto -occipital joints. Normal Measurements: 124° Significance : Angle is wider in condylar hypoplasia.

19. ATLANTOAXIAL DISLOCATION/INSTABILITY AAD is not a disease per se , rather it’s a manifestation of a spectrum of pathological states (Traumatic/ congenital/ inflammatory/multifactorial). AAD defined as an ADI : > 3mm in adults; > 5mm in children. ADI=distance between the odontoid process and the posterior border of the anterior arch of the atlas.

20. TYPES OF AAD:CLASSIFICATION ATLANTOAXIAL FACETAL DISLOCATION Type A: anterior atlantoaxial facetal dislocation Type B: posterior atlantoaxial facetal dislocation Type C: central atlantoaxial facetal dislocation LATERAL ATLANTOAXIAL FACETAL DISLOCATION ROTATORY ATLANTOAXIAL DISLOCATION Greenberg Classification(1968 ): Mobile and Reducible Fixed or Irreducible GREENBERG’S CLASSIFICATION: AAD may be due to- Incompetence of the odontoid process Incompetence of the Transverse ligament WADIA CLASSIFICATION : Group I: AAD with occipitalization of atlas & fusion of C2 & C3. Group II: odontoid maldeveloped. Group III: odontoid dislocation but no maldevelopment of dens or occipitalization of atlas. 57% of all CVJ anomalies. 8.3% of all causes of cervical compression

21. BASILAR INVAGINATION Goel et al in 1997 ; using a single criterion of the absence or presence of Chiari malformation , the anomaly was classified into Group I or Group II. Here he considered BI to be associated with the fixed or stable type of AAD and instability was not considered a defining factor in this classification. In a more recent study, stability of the atlantoaxial joint along with the fixity of the joint was considered and an Alternate classification of BI was proposed: Group A- AA joint was unstable and not fixed; Group B- AA joint was stable and fixed (Youmans 7 th E, cpt 324).

22. Current concepts : Atlantoaxial dislocations or instability is the primary cause of all types of Basilar Invagination . In a more acute form of BI, the facet dislocation is usually of type A . The more chronic form of BI is with types B or C atlantoaxial facet dislocation . “It is also recently proposed that Chiari 1 malformation and Syringomyelia, with or without bone malformations at the CV Junction may not be a primary phenomenon, but can be a response to atlantoaxial instability .”(Goel A. Journal of Neurosurgery: Spine. 2015 Feb.)

23. RULE OF SPENCE On the open-mouth odontoid view, the combined spread of the lateral masses of C1 on C2 should not exceed 6.9 mm. > 6.9 mm --rupture of the transverse ligament. POSTERIOR ATLANTODENTAL INTERVAL (PADI) This index may be more important because it more directly assesses the spinal canal width. Normal range: 19 –32 mm in males, 19–30 mm in females. < 19mm, neurological manifestations occur.

24. Platybasia Flat skull base/Martin’s anomaly; Flattening of the angle between the Clivus and the body of the sphenoid. It may be an isolated finding without associated basilar invagination. However, more often, basilar invagination is present. Can occur in conjunction with achondroplasia, osteogenesis imperfecta or secondary to Paget’s disease or other bone softening disorders. Usually asymptomatic; The basilar angle is > 152°. If plain film studies suggest platybasia, MRI evaluation is indicated as part of the necessary neurovascular evaluation.

25. Basilar invagination/impression Relative cephalad position of the upper cervical vertebra to the base of the skull. Two types of basilar invagination are described: Primary : Congenital, genetic predisposition; Often associated with other anomalies like occipitalization of the atlas, spina bifida occulta of the atlas, odontoid anomalies, agenesis or hypoplasia of the atlas, Klippel-Feil syndrome and Arnold-Chiari malformation. Secondary: An acquired condition that results from disease softening of the occipital bone in which the weight of the cranium deforms the base; The most common bone softening disorders that may precipitate this deformity are Paget’s disease, osteomalacia , fibrous dysplasia, and osteogenesis imperfecta; Inflammatory arthropathies cause cephalic migration of the dens as a result of transverse ligament destruction; Rheumatoid arthritis is the most common.

26. Tip of odontoid above McGregor’s line Tip of odontoid above Chamberlain’s line >7mm

27. Condylar hypoplasia The occipital condyles are underdeveloped and have a flattened appearance leading to basilar invagination and widening of atlanto occipital joint axis angle. The skull base normally descends medially. In the presence of condylar hypoplasia, the skull base is flattened or even ascends medially. The relationship between the tip of odontoid and lateral masses of the atlas with bimastoid line is violated.

28. Occipitalization of atlas Synonyms : atlas assimilation, atlanto-occipital fusion, block atlas. It is congenital synostosis of the atlas to the occiput caused by a failure of segmentation and separation of the most caudal occipital sclerotome during the first few weeks of fetal life. It is the most cephalic block vertebra of the spine and the most common anomaly of the craniovertebral junction. Pathology : Odontoid process protrudes through foramen magnum -> mechanical compression of anterior spinal artery, CSF outflow foramen, medulla and proximal spinal cord occurs. Loss of integrity of transverse ligament of atlas – may compress cord between atlas and dens (guillotine mechanism), causing vertebrobasilar ischemia and infarction

29. Clinical features: M:F = 5:1; Young; usually asymptomatic; symptoms usually occur 3 rd -4 th decade. Premature and severe joint disease at C1-C2; C2-C3. Associated with anomalies of the jaw, nose, ear, palate; cervical rib; Platybasia , basilar impression, Klippel-Feil. C2-C3 block vertebra is seen in 70% of cases. Non-segmentation patterns :- Complete fusion – Fusion of the anterior and posterior arches with the occiput as well as bilateral atlanto -occipital joint fusion. Incomplete fusion ( Hemioccipitalisation ) – isolated fusion of the anterior or posterior arch to the adjacent occiput and fusion or asymmetry of the C0–C1 articulations A rare variant is an anterior arch fused to basion and posterior arch fused to axis

30. Complete posterior arch agenesis Axis megaspinous sign

31. Os odontoideum The un-united odontoid process; is defined as the non-union of the dens with the axis body. A transverse, radiolucent cleft separates an ossicle of variable size from the axis body. The transverse ligament is usually intact. Normal development of dens: synchondrosis separating the base of dens from the body of C2 – normally ossifies by 5-7 years. The normal dense secondary ossification center for the odontoid process tip, a characteristic symmetrical V-shaped lucent zone of separation from the body of the dens

32. Klippel-Feil Syndrome Congenital brevicollis, cervical assimilation, cervical thoracic cage The classic triad consists of a low posterior hairline, short neck and limitation of neck movement. It is due to congenital segmentation defects of the cervical spine. Classification: KFS I – extensive cervical segmental fusion anomalies KFS II – one or two cervical block vertebrae KFS III - combined cervical, lower thoracic and lumbar fusion

33. Jefferson’s fracture: Results from axial loading injury and is described as the simultaneous disruption of the anterior and posterior arches of C1 with or without disruption of the supporting ligaments. The most common and second most common causes, respectively, are a fall from a height and a diving injury. The fracture usually occurs at the weakest point in the arch; The transverse ligament is of critical importance in maintaining the anatomic relation between the odontoid and anterior arch of C1. It is frequently avulsed because of trauma at the bony insertion site on C1. The clinical features are neck and suboccipital pain, dysphagia attributable to a retropharyngeal hematoma, and posterior fossa stroke or transient ischemic attack attributable to vascular damage.

34. Odontoid fracture: The mechanism of odontoid fracture is not well understood, but hyperflexion injury is believed to play a major role. MR imaging can display the relation of C1 to C2, disruption of the supporting ligaments, and spinal cord injury and compression. High-resolution CT may be better for detecting a subtle type I odontoid fracture. Type I: avulsion fracture of the tip of the dens at the insertion site of the alar ligament. Type 2: fracture at or above the junction of the dens and the central body. Type 3: fracture in the superior body and superior articular facets of C2.

35. CT Angiography VA anomaly, which can be clearly depicted by CTA, is more frequent in BI patients and rare in patients without CVJ abnormalities. Preoperative CTA should be performed for this patient population to prevent vascular injury. The risk of vascular injury may be increased when accompanied by an anomalous course of the vertebral artery at the CVJ, including persistent first intersegmental artery (PFIA), and fenestrated vertebral artery (FEN), and extracranial C1/2 origin of the posterior inferior cerebellar artery (PICA).

36. MANAGEMENT OF AAD Ref: Sweet 6E,pg 2059

37. References: Youmans and Winn neurological surgery 7th edition Ramamurthi & Tandon's textbook of neurosurgery 3 rd edition Internet THANK YOU