PMC7656000_01
Computed tomography (CT) of the cervical spine in right (a) and left (b) parasagittal planes demonstrates partial atlanto-occipital assimilation (AOA), with bilateral fractures causing up to 3 mm of distraction at the craniovertebral junction (arrows). Note that fracture involves the rudimentary left foramen transversarium; no evidence for vascular injury was identified on CT angiography, not shown. A midsagittal plane (c) demonstrates a small avulsion fracture just superior to the odontoid process (arrow). Platybasia and basilar invagination are present. A C1 posterior fusion anomaly is also suggested, but better appreciated on axial images, not shown. The basion-dens interval is mildly widened, but the atlantodental interval is preserved. A coronal reconstruction (d) emphasizes the AOA with superimposed traumatic dissociation of the occiput from the cervical spine.
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F1
CT of the cervical spine [Figure 1] revealed bilateral partial AOA with displaced fractures through the fused occipital condyles and lateral masses of C1 and a small avulsion fracture superior to the odontoid process of C2.
Three-dimensional volume-rendered reconstructions of the skull base from right (a) and left (b) posterolateral views best show the variable fusion between C1 and the skull base, as well as incidental posterior fusion anomaly of C1 (arrows). Coronal three-dimensional volume-rendered reconstruction (c) shows the fractures en face, which can be mistaken for a normal atlanto-occipital joint.
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F2
Three-dimensional reconstructions of the skull base [Figure 2] accentuated the abnormal morphology of the CVJ.
Mid-sagittal T1-weighted (a) and T2-weighted (b) magnetic resonance imaging of the cervical spine demonstrates discontinuity of the anterior atlanto-occipital membrane (horizontal white arrow) and apical ligament (diagonal white arrow), with associated edema and hematoma. The tectorial membrane is thinned, but intact (curved white arrow), and the transverse ligament (black arrow) is also intact. There is subtle signal hyperintensity in the spinal cord on the T2-weighted image (circle). The cerebellar tonsils are peg-like and extend up to 15 millimeters below the foramen magnum, resulting in inferior descent of the medulla and effacement of the spinal cord and thecal sac. A coronal T2 short-tau inversion recovery image (c) demonstrates intact alar ligaments (arrows), though due to the variant anatomy contiguity is difficult to appreciate on a single plane. An axial T2-weighted image at the level of C1-C2 (d) shows signal hyperintensity in the ventral left spinal cord, without signal hypointensity to indicate hemorrhage (circle). An axial T2-weighted image at the level of the foramen magnum (e) is notable for crowding of the foramen magnum due to inferior descent of the cerebellar tonsils related to Chiari I malformation, which compresses the brainstem and distorts its contour.
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F3
MRI of the cervical spine [Figure 3] demonstrated near-complete or complete tearing of the anterior atlanto-occipital membrane and apical ligament and thinning of the otherwise intact tectorial membrane.
CT of the cervical spine four weeks after injury, in right (a) and left (b) parasagittal planes, demonstrates near-complete osseous bridging of the fractures. The midsagittal plane (c) reveals that the basion-dens interval has decreased, emphasizing the congenital basilar invagination in this patient. The previously identified avulsion fragment superior to the dens has also resolved. A coronal reconstruction (d) confirms near-complete resolution of injury, with subtle residual fracture lucencies (arrows).
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F4
A follow-up CT of the cervical spine four weeks after injury [Figure 4] demonstrated near- complete osseous bridging of the fractures with improved alignment of his CVJ.