Os odontoideum

Os
odontoideum als Zufallsbefund. Kein Trauma in der Vorgeschichte bekannt. CT sagittal rekonstruiert.
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Os
odontoideum als Zufallsbefund. Kein Trauma in der Vorgeschichte bekannt. Röntgen seitlich.
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Teenager with
progressive spasticity. Sagittal CT without contrast of the cervical spine (left) shows a large well-corticated ossicle posterior and superior to the anterior arch of C1 and superior to the dens, hypertrophy of the anterior arch of C1, and a large atlanto-dens interval due to atlanto-axial dislocation. Sagittal T2 MRI without contrast of the cervical spine (right) shows a narrow spinal canal secondary to the atlanto axial dislocation with spinal cord compression and abnormal bright signal in the spinal cord at C1-C2.The diagnosis was dystopic os odontoideum.
pediatricimaging.org • CC-by-nc-sa 4.0
Os
odontoideum in wolcott-rallison syndrome: a case series of 4 patients. Radiological images from Case 1. a) Pre-operative sagittal midline CT (on bone windows) shows an os odontoideum widely separated from the body of C2 with a widening of the anterior atlanto-dental distance. There is a marked reduction in the sagittal bony canal dimensions between C2 body and the C1 posterior arch) b) Post-operative sagittal midline CT (on bone windows) demonstrates resection of the posterior arch of atlas and some reduction of the os odontoideum with a reduced distance between the os and the body of C2. c) Lateral plain radiograph demonstrates the occipito-cervical rod and screw fixation
ojrd.biomedcentral.com • CC-by-4.0
Os
odontoideum in wolcott-rallison syndrome: a case series of 4 patients. Radiological image from Case 2. Midline sagittal T2w image demonstrates lack of ossification of the dens
ojrd.biomedcentral.com • CC-by-4.0
Os
odontoideum in wolcott-rallison syndrome: a case series of 4 patients. Radiological images from Case 3. a Pre-operative CT scan showing C1-2 subluxation with antero-inferior subluxation of C1 lateral mass on C2; (b) pre-operative MRI images showing coronal and sagittal views of C2 demonstrating congenital dens hypoplasia with central dip typical of embryological abnormality and absence of posterior arch of C1; (c) post-operative XR image showing occipital C2 fixation following C1-2 reduction (C1 now in line with C2)
ojrd.biomedcentral.com • CC-by-4.0
nicht verwechseln mit: Persistierendes Ossiculum terminale
Radiopaedia • CC-by-nc-sa 3.0 • de

Os odontoideum (plural: ossa odontoidea) is an anatomic variant of the odontoid process of C2 and needs to be differentiated from persistent ossiculum terminale and from a type 2 odontoid fracture. It can be associated with atlantoaxial instability.

Although it was originally thought to be a congenital lesion due to a failure of the center of ossification of the dens to fuse with the body of C2, it may actually represent an unremembered and/or unrecognised fracture through the dens's growth plate before the age of 5 or 6. There may be associated instability and chronic symptoms .

The level of mobility is below the transverse band of the cruciform ligament and therefore results in abnormal mobility of the dens with respect to C2.

Subtypes

An os odontoideum can be divided into two main types :

  • orthotopic: normal position with a wide gap between C2 and os odontoideum
  • dystopic: displaced (dystopic os odontoideum has also been termed the "os avis" by some)
Associations

Often discovered incidentally on its own. Associated syndromes include:

It may be seen in association with another adjacent anatomic variant, the third condyle .

Radiographic features

  • smooth, well-corticated ossicle at the superior ossicle of a hypoplastic dens
  • around half the size of a normal dens
  • associated with hypertrophied and rounded anterior arch of the atlas

History and etymology

The Italian anatomist and neuroscientist Carlo Giacomini (1840-1898), first described the os odontoideum in humans in 1886. He is now better remembered for the band of Giacomini (in the hippocampal formation) and vein of Giacomini .

Differential diagnosis

Os odontoideum is one of the skeletal “don’t touch” lesions.

Siehe auch:
und weiter:
Assoziationen und Differentialdiagnosen zu Os odontoideum:
Pseudarthrose
Densfraktur
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Densfraktur
 
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Anomalien des
kraniozervikalen Übergangs
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Axis
Varianten
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