Management of basilar invagination and atlanto-axial subluxation via distraction of C1-C2 joint using intraarticular spacers and occipito-C2 fixation
by Cumhur Kilincer

History and examination
This 23-year-old female was admitted with complaints of diffuse neck pain, numbness in the arms, and occasional unsteady gait and dizziness for 2 years. There was no history of trauma or any other disease. The physical examination was normal. The neurologic examination revealed normal findings other than slightly increased deep tendon reflexes.
Cervical spine X-ray, computed tomography (CT), and magnetic resonance imaging (MRI) revealed a grossly anomalous cranio-cervical junction anatomy. The findings included: an occipitalized atlas, basilar invagination, atlanto-axial subluxation, Chiari type 1 malformation and cervical syringomyelia (Figures 1-4).

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Figure 1. Lateral X-ray shows absence of the posterior arch of atlas, and a tall/anomalous C2 body and thick lamina/spinous process.

Figure 2. Sagittal reconstructed CT images obtained in the neutral supine position. Middle view showed marked migration of the odontoid into the cranial cavity and atlanto-axial subluxation as evidenced by increased anterior atlanto-dental distance (6 mm) and decreased posterior atlanto-dental distance (18 mm). Right and left parasagittal cuts showed asymmetrical orientation of occipital condyles/C1 lateral masses/C2 articular surfaces at the right and left sides.

Figure 3. Further evaluation of median sagittal reconstruction of craniovertebral CT quantified basilar invagination: The odontoid process exceeded the McRae’s line (number 1; basion to opisthion) 8,2 mm; the Chamberlain’s line (number 2; hard palate to opisthion) 17,5 mm; the McGregor’s line (number 3; hard palate to the most caudal part of the occipital bone) 18,9 mm; and the Wackenheim’s line (number 4; the line along the clivus extending inferiorly to the cervical) 8,6 mm. All these values were well beyond the normal values described.

Figure 4. T2-weighted sagittal MRI showed migration of the cerebellar tonsils into the spinal canal (Chiari type 1), brainstem compression due to basilar invagination, and marked syringomyelia at the C3-C4 levels.

* 1. What would be your diagnosis?

* 2. How would you proceed?