PMC4093733_01
Preoperative images - Top row: X-ray and MRI of CVJ showing AAD. Adjacent to it is axial CT angio image showing C1 transverse foramina without vertebral artery (yellow arrows). VAs are seen medially (red arrows). Middle row: 2D CT angio images in parasagittal and coronal plane passing through C1-C2 joint showing acute C1 inferior sagittal facetal angle (yellow arrow) and bilateral inverted VA (red arrows). Bottom row: 3D CT angio showing bilateral inverted VA (red arrows) in relation to C1-C2 facet joint. The course of VA is akin to normal except that it passes inferior to transverse foramina and C1 facet
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F1
The computed tomography (CT) angiogram clearly defined the anomalous course of the V3 segments of both VA; the VA exited from the C2 transverse foramen, took a lateral course toward the C1 transverse foramen, but instead of traversing the C1 foramen, turned inferiorly and coursed medially beneath the C1 posterior arch before piercing the dura [Figure 1]. Therefore, both VA lay posterior to the inferior facet of C1 (3D CT; Figure 1).
Intraoperative images showing Bilateral anomalous VA's (*) and its horizontal course posterior to inferior C1 facet. The course can be traced from C2 transverse foramen and then ventral to the C2 root ganglion (# cut C2 root), forming a horizontal redundant loop posterior to the inferior C1 facets. Images show sequential exposure of bilateral C1-2 joints and placement of spacers with bone graft (BG). Note the gentle inferior retraction of the anomalous horizontal VA loop to expose the inferior C1 facet and placement of C1 screws leaving enough space to avoid its compression by the screw head
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F2
Next, the VAs were gently retracted inferiorly to insert the C1 lateral mass screws, which were sufficiently tightened to leave enough space between the screw head and the facet surface for the VA; the postoperative CT also showed adequate reduction [Figure 2 and 3].
(a and b) Midsagittal and coronal CT images showing complete reduction of Atlanto-axial dislocation. (c and d) parasagittal CT images passing through right and left C1 and C2 facets with screws and spacers. Note the flat drilled surface of C1 facets (white arrows) as compared with preoperative. Also note the adequate space between the posterior surface of inferior C1 facet and the screw head, enough to house the anomalous VA loop without compressing it
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F3
Next, the VAs were gently retracted inferiorly to insert the C1 lateral mass screws, which were sufficiently tightened to leave enough space between the screw head and the facet surface for the VA; the postoperative CT also showed adequate reduction [Figure 2 and 3].