Traumatic atlantoocipital dislocation in children

Clinical History

13-year-old male patient who suffered a fall from 2 metres while playing in a freight elevator.

Imaging Findings

The patient was a 13-year-old boy with severe cranioencephalic traumatism. Physical exploration demonstrated GCS (Glasgow coma scale) 6 and oedema in craniocervical region.

A craniocervical CT with multiplanar reconstruction was made in the emergency department, which showed a Wachenheim clivus line which did not intersect with the odontoid process, an abnormal Powers Ratio (1.4), an increased distance between the basion and the tip of the odontoid process (16mm) and finally an anterior displacement between the occipital condyles and the condylar surfaces of the atlas.

Vascular- CT was also made, which showed an absence of enhancement of V3 segments secondary to bilateral vertebral artery occlusions.

It was decided to perform an urgent craniocervical MR for evaluation of the spinal cord, extramedullary spaces and atlantooccipital joint (GE Medical Systems, Milwaukee, Wis. USA). MR showed a focal increased signal intensity in the upper cervical spine cord due to oedema.

Discussion

This entity has been rarely documented. It is a severe injury of the upper cervical spine with damage or rupture of tectorial membrane and alar ligaments. This injury is frequently fatal at the site of the accident; if the patient survives, neurologic sequelae including tetraplegia will be an issue.

Children have some peculiarities due to their anatomy, biomechanical characteristics and their young age, therefore, they are more prone to injury in upper cervical region [1].

Anatomic variants and incomplete or fusion ossification in the spine are common and may be mistaken for acute spinal injury [2].

Occipital dislocation was classified in 1986 by Traynelis [3] in four types: Type I with anterior displacement of the masses of the atlas; Type II with longitudinal displacement between the atlas and the occipital bone and Type III with posterior displacement. The longitudinal displacement, with true separation of the head of the spine, is the most common, followed by anterior displacement.

Plain lateral radiographs and axial CT cuts may miss lesions at the craniocervical junction, therefore coronal and sagittal CT reconstructions constitute the neuroimaging method of choice [4] . A distance more than 5mm between the occipital condyles and condylar surface of the atlas is suggestive of craniocervical injury [5]. Other measures to diagnose this entity is the Wachenheim clivus line (a line drawn along the posterior aspect of the clivus toward the odontoid process), it is abnormal when this line does not intersect or is tangential to the odontoid process [5]; also the Powers ratio (the ratio of the distance from the basion to posterior arch of the atlas divided by distance from anterior tubercle of atlas to opistion), is pathological when it is greater than one [5] and finally the distance between the basion and the tip of the odontoid is other measure, should be 12mm or less [5].

MR is indicated for evaluation of spinal cord, extramedullary spaces, ligamentous structures, joints and soft tissues [6].

CT angiography or MR angiography is useful to evaluate vascular injuries as dissection, posttraumatic pseudoaneurysm or vascular occlusion mainly.

In patients who survive the injury, treatment consists in fixation of the occiput to either C1 or C2.

Differential Diagnosis List

Final Diagnosis

Traumatic atlantooccipital dislocation.

URL:	https://eurorad.org/case/10963
DOI:	10.1594/EURORAD/CASE.10963
ISSN:	1563-4086