This educational presentation includes five different polytraumatized patients who presented at the Emergency Room (ER) of the Ospedale Maggiore Trauma Center in Bologna (Italy) and underwent a CT scan: four out of five of them were in dramatic clinical conditions (cardiac arrest or poor Glasgow Coma Scale (GCS) i.e. 3) and have been successfully diagnosed with AOD (cases 1, 2, 3, 4). One of them presented with GCS 8 and a distraction C6-C7 with diastasis: attention was focused on the positive findings and it led to initial misdiagnosis (case 5). 

Case 1 

M, 26 yo, high-speed motorcycle accident, cardiac arrest, presented at the ER after CPR (CardioPulmonary Resuscitation) intubated with poor GCS.

CT scan: atlo-occipital and atlo-axial multi-linear dislocation/fracture with posterior and anterior C1 arch detachment, right transverse foramen walls fracture and occipital condyles detachment.

Fig 3: Case 1. MPR parasagittal (A, B) and axial (C) CT scans: atlo-occipital and atlo-axial dislocation, with anterior displacement of the occiput relative to the atlas – Traynelis, type I (A, blue arrow), occipital condyles fracture and detachment (B, light blue arrows) and anterior and posterior C1 arch fractures (B, light blue dotted arrow; C)

Fig 4: Case 1. Measured parameters on MPR CT scans: - BDI (A), - BAI (B), - X-line (C).

Case 2 

F, 55 yo, pedestrian hit by a car, cardiac arrest, presented at the ER after CPR intubated in coma state.

CT scan: fracture of the occipital condyles, which appear asymmetrical to the lateral masses of the atlas.

Fig 5: Case 2. MPR parasagittal right (A) and left (B) CT scans: anterior dislocation of the condyles (blue arrow) – Traynelis type I.

Fig 6: Case 2. MPR coronal CT scans: fracture of the occipital condyles with asimmetrical widening of condyle-C1 joint spaces (A); measured CCI (B).

Case 3 

F, 65 yo, bike hit by a car, presented at the ER intubated with GCS 3.

CT scan: atlo-occipital joint spaces widening and also C6-C7 dislocation.

Fig 7: Case 3. MPR parasagittal right (A) and left (B) CT scans: anterior dislocation of the condyles (blue arrow) – Traynelis type I.

Fig 8: Case 3. Measured parameters on MPR sagittal and coronal CT scans: - BAI (A), - X-line (B, yellow lines), - CCI (C).

Fig 9: Case 3. MPR sagittal (A) and coronal (B) CT scans: C6-C7 dislocation.

Case 4 

M, 34 yo, high-speed motorcycle accident, cardiac arrest, presented at the ER after CPR intubated and with REBOA (Resuscitative Endovascular Balloon Occlusion of the Aorta).

CT scan: AOD with vertical distraction.

Fig 10: Case 4. MPR parasagittal right (A) and left (B) CT scans: AOD with vertical distraction – Traynelis type II.

Fig 11: Case 4. 3D reconstructions: vertical distraction of the occiput relative to the atlas – Traynelis type II.

Fig 12: Case 4. Measured parameters on MPR sagittal and coronal CT scans: - BAI (A), - Powers’ ratio (B: BP=50,3 mm; OA=31,7 mm; ratio=1,59), - X-line (C, yellow lines).

Case 5

M, 49 yo, polytrauma, presented at the ER with anisocoria and GCS 8.

CT scan: C6-C7 facet joint diastasis with anterior slip of the C7 soma; confirmation of C6-C7 intersomatic disc laceration in following MRI.

Fig 13: Case 5. MPR sagittal (A) CT scan shows C6-C7 intersomatic space enlargement with anterior slip of the C7 soma (light blue arrow). MPR axial CT scan confirms C6-C7 facet joint diastasis (B, light blue dotted lines) as compared to normal anatomy MPR axial CT scan (C). T2-W STIR sagittal MRI sequence: C6-C7 intersomatic hyperintensity, confirming disc laceration, and C6 posterior somatic wall shift as a posterior longitudinal ligament impairment (D).

MRI: undertaken 4 days after trauma, post C2-T2 surgical arthrodesis, to check for possible spinal cord damages. Articular rhyme between the C1 superior facet joint and occipital condyles is 6 mm wide on the right and 5 mm wide on the left, with T2 hyperintensity of intrarticular signal in relation to intrarticular effusion.

Fig 14: Case 5. T2-W parasagittal MRI sequence on the left (A) and right (B) show widening of atlo-occipital joint space with T2 hyperintensity of intrarticular signal in relation to intra-articular effusion.

Re-evaluation of the previous CT scan reveals anterior dislocation of the occipital condyles, which was overlooked in the first place as the C6-C7 diastasis acted as a distracting factor.

Fig 15: Case 5. Re-evaluation of the previous CT scan: MPR parasagittal right (A) and left (B) CT scans show anterior dislocation of the condyles (blue arrow) – Traynelis type I; C6-C7 facet joint diastasis is also visible (dotted blue lines).

Attention should also be focused on differential diagnosis such as other CCJ fractures: occipital condyle fractures, Jefferson fracture and odontoid fracture should be taken into account. They may be different entities but could also be associated with AOD: when present, condyle fractures may suggest looking for the entity and diagnosis may come in an easier way.

Fig 16: Condyle fractures may suggest looking for AOD: case 2 (A, B) and case 1 (C, D) MPR coronal and sagittal CT scans.

Fig 17: Differential diagnosis: three examples of Jefferson fracture (axial CT scans). Anterior and posterior arch fractures (A), posterior arch multi-fragmentary fracture (B), burst fracture (C).

Fig 18: Differential diagnosis: two examples of odontoid fracture on MPR CT scans (A, B: refer to the same patient; C,D,E: refer to another same patient).

AOD should also be differentiated from atlanto-axial subluxation, a C1-C2 disorder causing impairment in neck rotation (Fielding and Hawkins classification).

Fig 19: Differential diagnosis: atlanto-axial subluxation, axial CT scans on three different levels (A: upper; B: intermediate; C: lower) and 3D reconstructions (D: posterior view; E: anterior view).

If other spine fractures occur or especially in cases where no bone fractures are present, it may lead to misdiagnosis and as a matter of fact, it is always necessary to look for a regular continuity and congruence of anterior, posterior and spinolaminar spinal lines, double check the BDI/BAI and Powers' ratio and also don’t forget to look for swollen peri-spinal soft tissues.

One practical advice is to draw a line from the occiput going down to the axis on the sagittal plane of the cranial spine: this line, due to anatomical relations of the CCJ should be anteriorly convex. Any time this convexity is altered AOD should be suspected and considered.

Fig 20: Practical advice: to draw a line from the occiput going down to the axis on the sagittal plane of the cranial spine. A, B, C: normal anatomy: due to anatomical relations of the CCJ the line is anteriorly convex (light blue). In the presented cases of this educational presentation (case 1, D; case 2, E; case 3, E; case 4, G; case 5,H) this line (yellow) is never anteriorly convex (dotted light blue line show how it should phisiologically be).