LAUSR

BACKGROUND Craniocervical junction (CCJ) dislocations are often fatal. Atlanto-occipital dissociation (AOD) can be challenging to diagnose, especially among patients who present with absent or subtle radiological signs. CLINICAL DESCRIPTION A neurologically intact 37-year-old patient presented to our hospital following a high-speed motor vehicle accident. Initial CT scans showed normal CCJ anatomy, but a magnetic resonance imaging (MRI) of the CCJ was performed to further evaluate perimesencephalic subarachnoid hemorrhage (SAH). This revealed partial disruption of the anterior atlanto-axial membrane and tectorial membrane as well as complete disruption of the posterior atlanto-occipital membrane, the ligamentum flavum, and the apical ligament, signifying AOD. HALO spinal immobilization was performed in preparation for stabilization with posterior occipito-cervical fusion; however, the CCJ distracted widely during surgery due to the accident-related dislocation, signifying an unstable fracture. Postero-lateral fusion was performed, and the distraction injury was corrected via posterior surgical instrumentation. CONCLUSIONS Normal occiput-C1 craniometric parameters in the setting of unexplained perimesencephalic SAH does not eliminate the possibility of missed or delayed diagnosis of traumatic AOD injuries. Cervical MRI without contrast should be considered in patients with vertebral artery dissection or perimesencephalic SAH after a blunt injury with neck pain. When MRI shows evidence of disruption of two or more atlanto-occipital ligaments, surgical stabilization should be considered, as these are clinically very unstable injuries.