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Atul Gupta Neuroradiology. Overview  Os odontoideum (OO) is an uncommon craniovertebral junction (CVJ) abnormality characterized by a separate ossicle.

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Presentation on theme: "Atul Gupta Neuroradiology. Overview  Os odontoideum (OO) is an uncommon craniovertebral junction (CVJ) abnormality characterized by a separate ossicle."— Presentation transcript:

1 Atul Gupta Neuroradiology

2 Overview  Os odontoideum (OO) is an uncommon craniovertebral junction (CVJ) abnormality characterized by a separate ossicle superior to the dens.  Location: Orthotopic – In normal position at tip of dens Dystopic – Displaced towards base of occiput where it may fuse w/clivus or anterior ring of C1. Associated w/hypoplastic dens Spinal canal may narrowed in both types  Size/shape vary, smooth cortical borders  Leads to atlanto-axial instability (both types)  Transverse atlantal ligament is ineffective at restraining atlantoaxial motion.

3 A B C Dystopic OO. A. Coronal CT shows OO (arrow) fused with clivus. B. Coronal CT shows incomplete (right) C1. C. Axial view shows clefts involving C1 anteriorly & posteriorly & a dysplastic C2.

4 Dystopic OO. Midsagittal T1 WI shows large OO (arrow) fused with clivus, small anterior arch of C1, & narrowed spinal canal.

5 Orthotopic OO. A. Sagittal CT shows large OO (arrow) not fused with clivus but angled slightly anterior. B. Corresponding MR T1WI shows narrowed spinal canal. AB

6 Causes  Trauma  Congenital: Increased incidence in: ○ Morquio syndrome ○ Multiple epiphyseal dysplasia ○ Down’s Syndrome  There is continuing controversy over its etiology

7 Diagnosis o Usually incidentally detected or when symptoms occur o Open-mouth, anterior-posterior, and flexion- extension lateral radiographs o Gap separating the OO and axis proper should be above level of superior articular facets o Hypertrophy of anterior arch of C1 o 1 mm cuts sagittal CT reconstruction give more detail into the atlanto-axial junction o MRI – can help visualize spinal cord pathology, show space available for cord and provide ant-post canal dimensions o Fluoroscopy is recommended to show instability

8 AB Orthotopic OO. Flexion (A) & extension (B) radiographs show widening of atlantodental interval compatible with subluxation & instability.

9 Differential Diagnosis  Persistent ossiculum terminale  True hypoplasia of odontoid peg  Neurocentral synchondrosis  Odontoid fracture nonunion

10 Symptoms  Predisposes to increased risk of cranio- vertebral junction trauma  Acute neurological dysfunction with an insidious onset and: Torticollis Localized pain Neurovascular compromise signs  Cervicomedullary compromise may require neurosurgery in irreducible cranio-cervical stenosis.

11 Treatment  Monitor diagnosed patient for:  Motor dynamics – look for increase in multidirectional movement at cranio-vertabral junction indicating increased laxity of secondary ligaments  Monitor for neurological signs  Dorsal arthrodesis  Posterior atlantoaxial onlay fusion  Posterior atlantoaxial wiring and fusion  Posterior occipitocervical wiring and fusion  Posterior Magerl screw fixation and fusion  Harms technique of C1-2 fusion  Anterior resection of the os fragment  Posterior transarticular screw fixation


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