Os odontoideum is an anomaly where the tip of the odontoid process is divided by a wide transverse gap. This leaves the apical segment without its basilar support.
This anomaly is very rare and the exact incidence is unknown. While the exact etiology is not understood, it most likely represents an unrecognized fracture at the base of the odontoid or damage to the epiphyseal plate during the first few years of life.
Either of these can compromise the blood supply to the developing odontoid, resulting in the os odontoideum.
However another school of thought considers it a congenital anomaly.
Presentation
These children usually present with local neck pain, and occasionally transitory episodes of paresis [weakness of limbs], myelopathy, or cerebral-brainstem ischemia due to vertebral artery compression from the upper cervical instability.
Sudden death can occur, but is rare.
The neurologic symptoms are due to cord compression from posterior translation of the os into the cord in extension, or the odontoid into the cord in flexion. Increased motion at the C-1 to C-2 level can lead to vertebral artery occlusion ischemia of the
brainstem and posterior fossa structures, resulting in seizures, syncope, vertigo, and visual disturbances.
The long-term natural history is unknown.
Radiology
On radiographs, an os odontoideum is seen as an oval or round ossicle with a smooth sclerotic border located in the position of the normal odontoid tip. the size is variable.
There are three radiographic types of os odontoideum
- round
- Cone
- Blunt tooth
The base of the dens is usually hypoplastic. It is often difficult to differentiate an os odontoideum from nonunion following a fracture.
CT scans are useful to further delineate the bony anatomy. Fllexion-extension lateral radiographs are useful to assess instability.
Treatment
Non Operative Management
Observatio is sufficient in non symptomatic patients. Medical management of symptomatic patients consists of cervical traction, physical therapy, cervical collar use, and anti-inflammatory medications.
Opertive Management
Operative management is indicated in follwing settings
- Spinal instability
- Neurologic involvement
- Intractable pain
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