Occurrence and significance of odontoid lateral mass interspace asymmetry in trauma patients

The odontoid lateral mass interspace (OLMI) is the space between the lateral aspect of the dens axis and the medial circumference of the massa lateralis atlantis. The position of OLMI asymmetry as a normal variant or pathologic finding is an area of debate and clinical interest in trauma patients. We designed this prospective study to lay a framework for proposing strategies for the appropriate use of OLMI.

A total of 301 adult patients admitted for trauma were included. Computed tomography (CT) and magnetic resonance imaging (MRI) of the cervical spine were performed and examined for the presence OLMI asymmetry and bony/ligamentous lesions of the occipitoatlantoaxial complex.

Head rotation is linked to the occurrence of OLMI asymmetry. Reliable OLMI asymmetry evaluation is limited by observer agreement under a threshold value of 1.0 mm. In all, 86 patients (28.6 %) were found to have OLMI asymmetry on CT after trauma. Among these patients, 17.4 % had a bony/ligamentous lesion of the occipitoatlantoaxial complex. Among the patients without OLMI asymmetry, 8.8 % were found to have such lesions.

OLMI asymmetry should only be investigated by CT scans of the head in optimal position and with the threshold value of 1.0 mm. OLMI asymmetry should not be used alone as a sign of a cervical spine lesion. MRI should be performed if: (1) the physician has a high degree of suspicion of a cervical spine lesion; (2) OLMI asymmetry was demonstrated on a technically adequate CT scan; (3) clinical symptoms persist in patients with OLMI asymmetry when no acute MRI was performed.