Os Odontoideum

Summary

Os= bone
Odontoideum= refers to the odontoid process, a specific part of the second vertebra in the neck

Os odontoideum is a condition that involves the second vertebra (bone) in the neck. In os odontoideum, a specific part of this vertebra is detached from the rest of the bone.

The spine in the neck is called the cervical spine. The individual bones of the cervical spine, called vertebrae, are named according to a simple pattern. The names all start with the letter “C” for cervical, followed by a number that indicates their position. C1 is at the very top of the spine, just below the skull. C1 supports the weight of the skull. C2, the second vertebra, is underneath C1.

The joint between C1 and C2 is unusual–it allows much more movement than any other spinal joint. This is the joint that allows the head to turn, rotate and nod. One special feature of this joint is a peg of bone, about the size of the tip of a pinky finger, that sticks up from the front of C2.  It’s called the dens, or odontoid process, and it fits into a groove in C1.

In os odontoideum, the top of the dens is detached from the rest of C2.

Symptoms

Os odontoideum does not always cause symptoms. Many times, it is discovered “incidentally,” or during a scan performed for another reason.

When symptoms occur, they are usually caused by excessive and abnormal motion between the C1 and C2 vertebrae, resulting in stretching of the spinal cord or compression of the spinal cord by the os odontoideum. Symptoms may include neck pain, headache, torticollis (involuntary twisting of the neck), weakness, vertigo, lack of coordination, or paralysis.

Causes and Risk Factors

The cause of os odontoideum is not yet fully understood.

Since os odontoideum was identified in 1886, researchers have been attempting to determine whether the condition is congenital (something a person is born with) or if it develops gradually after an injury. Some cases of os odontoideum seem to fall in one category, and some cases in the other. It is possible that some cases fall in both—that is, people are predisposed to developing the condition, but only do so after injury.

People with Down syndrome or Morquio syndrome are more likely to have os odontoideum than people without those syndromes.

Tests and Diagnosis

X-rays are normally used to diagnose and follow the progress of os odontoideum. X-rays use invisible beams of electromagnetic radiation to produce images of bone on film. The X-rays may be taken from a few angles, and in a few positions. Dynamic images may also be taken with the patient flexing and then extending the neck. This helps visualize the bones and assess the stability of the joint.

CT (computed tomography) and/or MR (magnetic resonance) imaging scans may also be used to visualize the bone or its effects on soft tissue. CT scans use a computer and X-rays; they give more detail than plain X-rays.

MR scans use a magnet and radio waves to produce detailed images of bones and soft tissue.

Treatments

In some cases of os odontoideum, scans reveal a stable joint. This is often the case when the condition is discovered incidentally and no symptoms are present. A stable joint will usually not need additional surgical stabilization.

Surgical treatment may be indicated if the C1-C2 joint appears unstable; if neurological symptoms like pain, weakness, or dizziness are present; or if there is pain that does not respond to nonoperative treatment.

The main surgical option is fusion and fixation, or the use of surgical instruments and bone grafts to re-attach the dens to the rest of C2. Spinal stabilization with metallic screws, rods or thin titanium cables will usually be performed. This surgery is performed with a posterior approach, or via the back of the neck. Our neurosurgeons can tailor a treatment plan to each specific patient and situation.

Preparing for Your Appointment

Drs. Paul C. McCormick, Michael G. Kaiser, Peter D. Angevine, Alfred T. OgdenChristopher E. MandigoSheng-fu (Larry) Lo and Richard C.E. Anderson (Pediatric) specialize in the treatment of os odontoideum.  Each can also offer you a second opinion.

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