MRI may be used to identify potentially unstable occult ligamentous or soft tissue injury. Note: an abnormal signal on MRI is not always associated with instability on flexion-extension X-rays 1). It has been recommended that this MRI should be done within 48 hours 2) or 72 hours 3) of injury. MRI is not reliable for identifying the osseous injury.
Abnormal MRI findings include: abnormal high signal on T2WI in the occipitoatlantal joints or in the posterior occipitoatlantal (O-C1) ligaments. Very sensitive (≈ 100%) but not specific for unstable AOD. The figure at left shows abnormal signal in the posterior O-C1 ligaments (arrow 1) and in the ligamentum flavum and soft tissues (arrow 2).
Indications for non-emergent MRI (modified):
1. inconclusive cervical spine radiography, including questionable fractures
2. significant midline paraspinal tenderness and patient unable to have flexion-extension X-rays
3. obtunded or comatose patients
1. ventral signal abnormalities with prevertebral swelling
2. dorsal signal abnormalities. Abnormal signal limited to the interspinous is probably not as unstable as when it extends into the ligamentum flavum 4). These patients were treated with rigid collars or Minerva jackets for 1–3 months, and one that was felt to be very unstable underwent fusion.
3. disc disruption indicated disc disruption indicated by abnormal signal intensity within the disc, increased disc height, or frank disc protrusions