A patient who sustained a flexion/lateral bending cervical spine injury presented with an asymmetric odontoid process. The asymmetry was confirmed on computed tomography (CT) and shown on magnetic resonance imaging (MRI) to be due to a unilateral alar ligament injury. The finding of an asymmetric odontoid process should not be automatically discounted as malpositioning.

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Figure 1 (A) Open mouth plain radiograph of the asymmetric odontoid process. (B) Axial T2-weighted magnetic resonance image demonstrating an area of high signal intensity (fluid) in the site expected to be occupied by the left alar ligament.

A 23-year-old woman presented with neck pain following a high-speed road traffic accident. At the time of the frontal impact, her head was turned to the left. There was no cervical tenderness, full active motion and no neurological deficit. A lateral cervical spine radiograph revealed no abnormal findings, but asymmetry of the odontoid process was noted on all open mouth radiographs. Two days later she noticed clicking in the upper cervical spine in extremes of rotation. Further imaging with CT confirmed the asymmetry of the odontoid process. No cervical spine fracture was found. Subsequent MRI demonstrated an isolated left-sided alar ligament injury. The patient was conservatively managed with a supporting collar for 6 weeks.

Isolated alar ligament injury is a recognised entity following a whiplash with the head turned.1 Diagnosis of this injury is further suspected when odontoid asymmetry is found in an adequate open mouth radiograph.