![]() Here we present the case of a patient with an incidentally discovered os odontoideum and review the embryological aspects and relevant upper cervical spinal anatomy and literature. 1 The following management option was given for patients with incidental os odontoideum based on the available Class III data: “Patients with os odontoideum, either with or without C1–2 instability, who have neither symptoms nor neurological signs may be managed with clinical and radiographic surveillance.” Even so, the authors acknowledged that patients with C1–2 instability are at risk for future spinal cord damage and that surgical stabilization and fusion of C1–2 is “meritorious.” In fact, the literature regarding the management of os odontoideum remains limited to Class III data. In an article in the “Guidelines for the Management of Acute Cervical Spine and Spinal Cord Injuries” supplement published in 2002 jointly by the American Association of Neurological Surgeons and the Congress of Neurological Surgeons, the authors reviewed the available literature on os odontoideum and found no Class I or Class II data to generate treatment standards or guidelines. Most spine surgeons agree that patients with signs or symptoms of neurological dysfunction should undergo stabilization, but the role for surgical stabilization in asymptomatic patients and those with neck pain alone remains controversial. Os odontoideum may be discovered as part of a workup for neck pain and/or neurological symptoms, but it is also often found incidentally. It appears as a smooth-margined, apical osseous segment separated from the base of the odontoid process by an obvious gap. O s odontoideum is an anatomical abnormality in which the tip of the odontoid process lacks continuity with the body of C-2. ![]() When atlantoaxial instrumentation is used, fusion rates for os odontoideum should approach 100%. ![]() This recommendation is bolstered by the fact that surgical fusion of the C1–2 region has evolved greatly and can now be done with considerable safety and success. These subgroups include those who are young, have anatomy favorable for surgical intervention, and show evidence of instability on flexion-extension cervical spine x-rays. The authors' clinical experience leads them to believe that certain subgroups of asymptomatic patients should be strongly considered for surgery. Although there is little debate that patients with os odontoideum and clinical or radiographic evidence of neurological injury or spinal cord compression should undergo surgery, the dispute continues regarding the care of asymptomatic patients whose os odontoideum is discovered incidentally. The consequences of this instability are exemplified by numerous cases in the literature in which a patient with os odontoideum has suffered a spinal cord injury after minor trauma. By definition, the presence of an os odontoideum renders the C1–2 region unstable, even under physiological loads in some patients. The spectrum of presentation is striking and ranges from patients who are asymptomatic or have only neck pain to those with acute quadriplegia, chronic myelopathy, or even sudden death. The genesis of os odontoideum is thought to be prior bone injury to the odontoid, but a developmental cause probably also exists. Os odontoideum was first described in the late 1880s and still remains a mystery in many respects.
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