Abstract
Os odontoideum is a rare entity of the second cervical vertebra, characterized by a circumferentially corticated ossicle separated from the body of C2. The ossicle is a distinct entity from an odontoid fracture or a persistent ossiculum terminale. The diagnosis may be made incidentally on imaging obtained for the workup of neck pain or neurologic signs and symptoms. Diagnosis usually can be made with plain radiographs. MRI and CT can assess spinal cord integrity and C1-C2 instability. The etiology of os odontoideum is a topic of debate, with investigative studies supporting both congenital and traumatic origins. A wide clinical range of symptoms exists. Symptoms may present as nondescript pain or include occipital-cervical pain, myelopathy, or vertebrobasilar ischemia. Asymptomatic cases without evidence of radiologic instability are typically managed with periodic observation and serial imaging. The presence of atlantoaxial instability or neurological dysfunction necessitates surgical intervention with instrumentation and fusion for stability.