CASE 47

By: Dr. Mai Mattar, MD and Dr. Nizar Al-Nakshabandi MD, FRCPC

HISTORY: 24-year-old male known case of ankylosing spondylitis was involved in a road traffic accident.

What are your findings?

What is the differential diagnosis?

What are the causes?

FINDINGS:

Sagittal T1, T2FS (A, B) and axial T2 weighted images (C) demonstrate a widening of the predental space in keeping with atlantoaxial subluxation. There is edema within the odontoid process with no obvious fracture.

DIFFERENTIAL DIAGNOSIS:

• Atlanto-axial subluxation.

• Odontoid fracture.

DIAGNOSIS:

Atlantoaxial subluxation.

PEARLS AND DISCUSSION:

Atlantoaxial subluxation occurs at the C1-C2 level causing malfunction and rotation of the neck. The anterior facet of C1 is fixed on the facet of C2. Dislocation of the lateral masses of C1 on C2 can occur.

Distance between the anterior surface of the dens and the posterior surface of the tubercle of C1 is usually less than 3 mm in adults at 5 mm or less in children.

In atlantoaxial instability: There is an increase in the pre-dentate space of more than 3 mm in adults and more than 5 mm in children.

Spinal canal is widest at the level of C2 and should not be less than 18 mm in the widest AP dimension.

Mechanism of injury is either by anterior-posterior subluxation, rotatory subluxation, vertical subluxation, or lateral subluxation.

Acquired causes from trauma and retropharyngeal abscesses are most common.

Arthritides such as rheumatoid arthritis, psoriasis, and Reiter’s syndrome have been implicated but in real practice rheumatoid arthritis is the most common cause.

Congenital causes such as os odontoideum, Down syndrome or Morquio syndrome.

Treatment is by surgical fusion of C1-C2.

FURTHER READING:

1. Rojas CA, Hayes A, Bertozzi JC et-al. Evaluation of the C1-C2 articulation on MDCT in healthy children and young adults. AJR Am J Roentgenol. 2009;193 (5): 1388-92. 

2. Fielding JW, Hawkins RJ. Atlanto-axial rotatory fixation. (Fixed rotatory subluxation of the atlanto-axial joint). J Bone Joint Surg Am. 1977;59 (1): 37-44.

3. Reynolds MD. Lateral subluxation of atlanto-axial joint. Ann. Rheum. Dis. 1980;38 (5): 499.