atlanto-axial subluxation
Infant in
motor vehicle accident with neck painAxial CT without contrast of the cervical spine obtained after the accident shows C1 vertebral body rotated 45 degrees to the right (upper left) on the C2 vertebral body (lower left). Axial CT without contrast of the cervical spine obtained 1 day later shows C1 vertebral body now normally aligned (upper right) with the C2 vertebral body (lower right)The diagnosis was atlanto axial rotatory subluxation that resolved in a day
Infant with
torticollis since birthAxial CT without contrast of the cervical spine shows the C1 vertebral body rotated to the left approximately 45 degrees in relation to the C2 vertebral body.The diagnosis was atlanto-axial rotatory subluxation without a demonstrated etiology.
Preschooler
who developed torticollis after watching a video on their tablet with their neck flexed for 8 hours without moving3D CT without contrast of the cervical spine shows the C1 vertebral body rotated to the left approximately 30 degrees in relation to the C2 vertebral body.The diagnosis was atlanto-axial rotatory subluxation due to muscle spasm.
Preschooler
with fever and torticollisAxial images with bone windows from a CT with contrast of the neck shows the C1 vertebral body (above left) rotated approximately 30 degrees to the right in relation to the C2 vertebral body (above right). Axial image with soft tissue windows (below) from the same CT shows a low density fluid collection with an enhancing rim to the left of midline in the retropharyngeal space.The diagnosis was atlanto-axial rotatory subluxation due to a retropharyngeal abscess.
School ager
with juvenile idiopathic arthritis with neck pain and torticollis for 6 weeksAxial images from a CT without contrast of the cervical spine shows the C1 vertebral body rotated to the left approximately 45 degrees (top) in relation to the C2 vertebral body (middle). A MIP image (bottom) better demonstrates the rotation of C1 on C2.The diagnosis was atlanto-axial rotatory subluxation due to juvenile idiopathic arthritis.
Neuroimaging
assessment in Down syndrome: a pictorial review. Sagittal cervical CT of a 68-year-old Down syndrome patient, showing the presence of an os odontoideum with atlanto-axial and atlanto-odontoid luxation; there is severe stenosis of the craniocervical junction, with space conflict in the bulbo-medullary junction
Teenager with
progressive spasticity. Sagittal CT without contrast of the cervical spine (left) shows a large well-corticated ossicle posterior and superior to the anterior arch of C1 and superior to the dens, hypertrophy of the anterior arch of C1, and a large atlanto-dens interval due to atlanto-axial dislocation. Sagittal T2 MRI without contrast of the cervical spine (right) shows a narrow spinal canal secondary to the atlanto axial dislocation with spinal cord compression and abnormal bright signal in the spinal cord at C1-C2.The diagnosis was dystopic os odontoideum.
Os
odontoideum in wolcott-rallison syndrome: a case series of 4 patients. Radiological images from Case 1. a) Pre-operative sagittal midline CT (on bone windows) shows an os odontoideum widely separated from the body of C2 with a widening of the anterior atlanto-dental distance. There is a marked reduction in the sagittal bony canal dimensions between C2 body and the C1 posterior arch) b) Post-operative sagittal midline CT (on bone windows) demonstrates resection of the posterior arch of atlas and some reduction of the os odontoideum with a reduced distance between the os and the body of C2. c) Lateral plain radiograph demonstrates the occipito-cervical rod and screw fixation
Os
odontoideum in wolcott-rallison syndrome: a case series of 4 patients. Radiological image from Case 2. Midline sagittal T2w image demonstrates lack of ossification of the dens
Os
odontoideum in wolcott-rallison syndrome: a case series of 4 patients. Radiological images from Case 3. a Pre-operative CT scan showing C1-2 subluxation with antero-inferior subluxation of C1 lateral mass on C2; (b) pre-operative MRI images showing coronal and sagittal views of C2 demonstrating congenital dens hypoplasia with central dip typical of embryological abnormality and absence of posterior arch of C1; (c) post-operative XR image showing occipital C2 fixation following C1-2 reduction (C1 now in line with C2)
Preschooler
with Trisomy 21. Lateral radiographs of the cervical spine show a mildly enlarged atlanto dens interval in neutral position (left), that increases significantly on flexion (center) and reduces on extension (right).The diagnosis was atlanto axial instability in a patient with Trisomy 21.
Atlanto-axial subluxation is a disorder of C1-C2 causing impairment in rotation of the neck. The anterior facet of C1 is fixed on the facet of C2. It may be associated with dislocation of the lateral mass of C1 on C2.
Pathology
Etiology
- congenital
- arthritides
- acquired
- trauma
- retropharyngeal abscess / Grisel syndrome
- surgery
- upper respiratory tract infection
Mechanism
There are several ways in which a subluxation can occur:
- anteroposterior subluxation
- rotatory subluxation, known as atlantoaxial rotatory fixation (AARF) is characterized into four different types :
- type I: the atlas is rotated on the odontoid with no anterior displacement
- type II: the atlas is rotated on one lateral articular process with 3 to 5 mm of anterior displacement
- type III: comprises a rotation of the atlas on both lateral articular processes with anterior displacement greater than 5 mm
- type IV: characterized by rotation and posterior displacement of the atlas
- vertical subluxation
- lateral subluxation
Radiographic features
Plain radiograph
In a non-traumatic setting flexion and extension views may be performed. The expected distance between anterior arch of C1 and the dens in the fully flexed position should be <3 mm in an adult (~5 mm in a child).
In a vertical subluxation, the dens is often above the McGregor line by over 8 mm in men and 9.7 mm in women.
CT
On CT, C1 is not oriented in line with the head. The head may be pointed anteriorly, C1 is turned. If this is a fixed defect, C2 is rotated in conjunction with C1.
Differential diagnosis
Possible differential considerations on imaging include:
Siehe auch:
Assoziationen und Differentialdiagnosen zu atlantoaxiale Subluxation:
