On different imaging modalities, a number of osseous reference points in this region are used to draw different lines and angles, which allows us to define the characteristics of the junction:
- Chamberlain and Mc Gregor lines are drawn from the hard palate either to the opisthion, or to the lowest point of the occipital squamosal surface, respectively (Fig. 1). These lines assess the odontoid process relations, normally it is tangent or lies below to them (2) and the anterior arch of the atlas typically lies below both lines (2,3).
- The Mc Rae line, from basion to opisthion (anterior and posterior margin of the foramen magnum) (Fig. 1) allows for the assessment of cranial content descent (4).
![](https://epos.myesr.org/posterimage/esr/ecr2020/154355/media/864396?maxheight=300&maxwidth=300)
Fig. 1: FINDINGS: Craniometric lines: Chamberlaine line, Mc Gregor line and Mc Rae line (5).
References: 5. A. B. Gil Guerra et al. Cranio-cervical junction: craniometry and anomalies. 10.1594/ecr2018/C-1697.
- Wackenheim or basilar line is drawn along the clivus, extending it inferiorly to the upper cervical canal (2-4). The posterior aspect of the odontoid process must to be tangent to this line (3,4).
- The Welcher basal angle, formed between the nasion-tuberculum line and basion-tuberculum line (Fig 2), goes beyond 140º when the skull base is abnormally flattened, known as platybasia (2,3).
![](https://epos.myesr.org/posterimage/esr/ecr2020/154355/media/864397?maxheight=300&maxwidth=300)
Fig. 2: FINDINGS : Schematic diagram showing Welcher basal angle (5).
References: 5. A. B. Gil Guerra et al. Cranio-cervical junction: craniometry and anomalies. 10.1594/ecr2018/C-1697.
· The cervical spine is the most mobile portion of the spine. The occipito-atlantoaxial complex serves as a transition zone between the vertebral structures and the skull.
· The unique anatomical configuration of the craniovertebral junction creates distinct biomechanical behavior that differs from other spinal joints.
· The disorders of the CVJ could be either Congenital, developmental and acquired or metabolic and genetic disorders which are summarised in the table below (6) (Table 1, 2,3).
· The complex osseous relationships of the CVJ is encompassed with multiple neurovascular structures, thus making the radiologic evaluation a challenging one at this region.
· The commonest congenital CVJ anomalies were atlantoaxial dislocation, Arnold chiari malformation and less common are occipital assimilation and basilar invagination(7).
· ACM I and Syringomyelia are the commonest neural anomalies associated with bony CVJ anomalies(7).
· The commonest injuries involving the CVJ were odontoid fracture predominantly type II and the commonest combination of injury was C1 with odontoid fracture(7).
· The clinical features of lesions at the CVJ are diverse and depend completely on the type and degree of deformity of the regional structures. The vital structures, including the brain stem, upper cervical spinal cord, cervical nerve roots, vertebral arteries, and anterior spinal artery, can become compressed. Suboccipital and neck pain (encountered in 82% of patients with CVJ lesions) is the most common sign. Brain stem, lower cranial nerve, and spinal cord compression may cause sleep apnea, dysphagia, nystagmus, dysphasia, nasal (6).
CONGENITAL MALFORMATIONS
TABLE 1
Malformations of occipital bone
|
Malformations of the atlas
|
Malformations of the axis and odontoid process
|
· Platybasia
·Basioccipital hypoplasia (basilar invagination)
· Condylar hypoplasia
·Condylar dysplasia (condylus tertius, paracondyloid process, and basilar process)
|
· Atlas assimilation
· Aplasia and hypoplasia of the atlas
· Atlas arch anomaly
|
· Aplasia or hypoplasia of the dens
· Persistent ossiculum terminale
· Os odontoideum
· Klippel-Feil anomaly
|
DEVELOPMENTAL AND ACQUIRED
TABLE 2
Traumatic
|
Inflammation and degenerative arthritis
|
Infectious
|
Neoplastic
|
· Clival fractures
· Occipital condyle fractures
· Atlanto-occipital dislocations
· Atlas fractures, including Jefferson’s fractures
· Axial fractures, including odontoid fracture
· Hangman’s fractures
|
· Rheumatoid arthritis
· Seronegative spondyloarthropathy
· Others arthritidis (gout, CPPD, amyloidosis, pseudotumor)
· Degenerative arthritis
· OPLL and diffuse idiopathic skeletal hyperostosis
|
· Pyogenic (eg, Grisel’s syndrome)
· Granulomatous (tuberculosis and others)
· Epidural abscess
|
· Benign( ABC, FD, osteoblastoma, osteochondroma, and chondroma
· Malignant (chondrosarcoma, multiple myeloma, metastases etc)
|
METABOLIC AND GENETIC DISORDERS
TABLE 3
Metabolic
|
Genetic transformations
|
· Morquio’s syndrome
· Conradi’s syndrome
· Fetal warfarin syndrome
· Renal rickets
|
· Down’s syndrome
· Osteogenesis imperfect,
· Achondroplasia,
· Paget’s disease,
· Neurofibromatosis
|