Odontoid lateral mass asymmetry: do we over-investigate?

Objectives: This study aimed to evaluate the necessity for further radiological investigation in patients with suspected traumatic rotatory subluxation of the atlanto- axial complex on plain radiography following acute cervical trauma and outline guidelines for assessment of patients with atlanto- axial asymmetry on plain radiography. Methods: A retrospective review of all patients who had undergone atlanto- axial CT scanning as a result of radiographic C1 - C2 asymmetry following cervical spine trauma. The plain x ray and CT images were reviewed retrospectively and correlated with the clinical presentation and outcome. Results and conclusion: Records of 29 patients ( 16 men, 13 women; age range 21 - 44 years) were reviewed. All patients were found to have atlanto- odontoid asymmetry on the initial plain x ray. CT images of none of the patients revealed rotatory subluxation. Ten patients ( 32%) were found to have congenital odontoid lateral mass asymmetry. All patients were treated conservatively without any further intervention. On review, in 19 patients the orientation of the x ray beam in combination with head rotation was found to be at fault. Approximately 1050 trauma cervical spine x rays were taken in the department where this study was conducted over the period 1999 - 2001. This study identified 10 patients out of a total of 29 as having congenital odontoid lateral mass asymmetry. This represents approximately 1% of the patients attending the emergency department. Thus congenital odontoid lateral mass asymmetry should be considered in the differential diagnosis following acute cervical trauma.