Age / Sex : 32 / M

Chief complaint: Traffic accident (Pedestrian), 3 hours ago

At the time of ER visit, the patient was unconscious, and had multiple trauma.

What is your diagnosis?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).

Courtesy : Dong Hyun Kim, SMG-SNU Boramae Medical Center

Discussion

Answer: Atlanto-Occipital Dissociation

Findings:

Increased basion-dens interval (yellow line, 1.5cm) and swelling and obliteration of fat plane adjacent preverterbal and posterior cervical area (yellow arrows).

MR image show disruption of the tectorial membrane, apical, and anterior longitudinal ligaments (orange arrows), with adjacent preverterbal and posterior cervical soft tissue edema or hemorrhage. There is a spinal cord injury at C1-2 level (rad arrow).

Differential Diagnosis:

1. Occipital condyle fracture


2. Jefferson fracture: anterior and posterior C1 ring fracture, possible lateral masses displacement


3. Odontoid fracture: type 2 will cause posterior dens displacement and will disrupt Powers ratio


4. Atlanto-axial subluxation: atlantoaxial rotatory fixation will cause C1 lateral mass asymmetry. relative to the dens


5. Down syndrome: atlanto-occipital instability due to laxity of alar ligament


6. Rheumatoid arthritis: CT/MRI will show atlantooccipital instability due to pannus destabilisation of joints and ligaments, and radiography will show erosions

Discussion:

Atlanto-Occipital Dissociation

The mechanisms of injury are believed to be extreme hyperextension with injury to the tectorial membrane, accompanied by lateral flexion

The tectorial membrane and alar ligaments provide most of the stability to the atlanto-occipital joint, and injury to these ligaments results in instability due to low inherent osseous stability

Radiographic features (Cervical spine lateral)

• basion-dens interval (BDI) >10 mm in adults


• basion-axial interval (BAI) >12 mm in adults


• Powers ratio >1 (insensitive to a vertical distraction injury or posterior dissociation)

Evaluation for proximal spinal cord injury, as well as for other injuries such as traction of the lower cranial nerves or the upper cervical roots, is crucial

References:

1. Rojas CA, Bertozzi JC, Martinez CR et-al. Reassessment of the craniocervical junction: normal values on CT. AJNR Am J Neuroradiol. 2007;28 (9): 1819-23. AJNR Am J Neuroradiol


2. Hall GC, Kinsman MJ, Nazar RG et-al. Atlanto-occipital dislocation. World J Orthop. 2015;6 (2): 236-43.


3. Riascos R, Bonfante E, Cotes C et-al. Imaging of Atlanto-Occipital and Atlantoaxial Traumatic Injuries: What the Radiologist Needs to Know. Radiographics. 2015;35 (7): 2121-2134.


4. Pang D, Nemzek WR, Zovickian J. Atlanto-occipital dislocation--part 2: The clinical use of (occipital) condyle-C1 interval, comparison with other diagnostic methods, and the manifestation, management, and outcome of atlanto-occipital dislocation in children. (2007) Neurosurgery. 61 (5): 995-1015


5. https://radiopaedia.org/articles/atlanto-occipital-dissociation-injuries?lang=us