Occipitocervical fusion of traumatic atlanto-occipital dissociation in a patient with autofused cervical facet joints: illustrative case

Abstract

Background: Patients who survive traumatic atlanto-occipital dissociation (AOD) may present with normal neurological examinations and near-normal-appearing diagnostic images, such as cervical radiographs and computed tomography (CT) scans.

Observations: The authors described a neurologically intact 64-year-old female patient with a degenerative autofusion of her right C4-5 facet joints who presented to their center after a motor vehicle collision. Prevertebral soft tissue swelling and craniocervical subarachnoid hemorrhage prompted awareness and consideration for traumatic AOD. An abnormal occipital condyle-C1 interval (4.67 mm) on CT and craniocervical junction ligamentous injury on magnetic resonance imaging (MRI) confirmed the diagnosis of AOD. Her autofused right C4-5 facet joints were incorporated into the occipitocervical fusion construct.

Lessons: Traumatic AOD can be easily overlooked in patients with a normal neurological examination and no associated upper cervical spine fractures. A high index of suspicion is needed when evaluating CT scans because normal values for craniocervical parameters are significantly different from the accepted ranges of normal on radiographs in the adult population. MRI of the cervical spine is helpful to evaluate for atlanto-occipital ligamentous injury and confirm the diagnosis. Occipitocervical fusion construct may need to be extended to incorporate spinal levels with degenerative autofusion to prevent adjacent level degeneration.

Keywords: AOD = atlanto-occipital dissociation; BAI = basion-axial interval; BDI = basion-dens interval; CCI = condyle–C1 interval; CT = computed tomography; MRI = magnetic resonance imaging; PAL = posterior axial line; STIR = short tau inversion recovery; atlanto-occipital dislocation; atlanto-occipital dissociation; degenerative facet fusion; facet joint autofusion; occipitocervical fusion.

FIG. 1.

Initial CT of the head demonstrating subarachnoid hemorrhage ventral to the medulla (arrow; A) and within the left posterior Sylvian fissure (arrow; B).

FIG. 2.

A: Coronal CT of the cervical spine demonstrating splaying of right occiput–C1 and C1–2 space relative to left side (circle). B: Sagittal CT demonstrating splayed segments on right side with some air in occiput–C1 space (yellow arrows) as well as fused right C4–5 facet (blue arrow).

FIG. 3.

A: Calculation of BDI is 10.1 mm. B: Calculation of basion-PAL is 11.9 mm. C: Powers ratio, which equals the ratio between the distance of the basion to the posterior arch of C1 (red line) over that of the opisthion to the anterior arch of C1 (blue line), is 1.13. D: Calculation of the occipital CCI is 4.67 mm.

FIG. 4.

Sagittal MRI of the cervical spine without gadolinium showing STIR (A) and T2-weighted imaging (B) signal hyperintensity at the craniocervical junction, suggesting ligamentous injury. Specifically, injury to the atlanto-occipital ligament (B, green arrow), apical ligament (B, purple arrow), tectorial membrane (A, orange arrow), transverse ligament (A, dark blue arrow), and posterior ligamentous complex (A and B, yellow asterisks) was observed. Prevertebral edema from basion to C5 is also apparent (A and B, light blue arrows). Axial MRI (C) of the cervical spine without gadolinium demonstrating epidural blood (red arrow) seen in the cervicomedullary junction toward the right side.

FIG. 5.

Postoperative upright radiographs showing good alignment of occiput to cervical spine in the anteroposterior (A) and lateral (B) views.