OS Odontoideum
Download
Report
Transcript OS Odontoideum
Atul Gupta
Neuroradiology
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.
B
A
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.
Dystopic OO. Midsagittal T1
WI shows large OO (arrow)
fused with clivus, small
anterior arch of C1, &
narrowed spinal canal.
A
B
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.
Causes
Trauma
Congenital:
Increased incidence in:
○ Morquio syndrome
○ Multiple epiphyseal dysplasia
○ Down’s Syndrome
There is continuing controversy over its etiology
Diagnosis
o
o
Usually incidentally detected or when symptoms
occur
Open-mouth, anterior-posterior, and flexionextension 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
o
o
1 mm cuts sagittal CT reconstruction give more
detail into the atlanto-axial junction
MRI – can help visualize spinal cord pathology,
show space available for cord and provide ant-post
canal dimensions
Fluoroscopy is recommended to show instability
A
B
Orthotopic OO. Flexion (A) & extension (B) radiographs
show widening of atlantodental interval compatible with
subluxation & instability.
Differential Diagnosis
Persistent ossiculum terminale
True hypoplasia of odontoid peg
Neurocentral synchondrosis
Odontoid fracture nonunion
Symptoms
Predisposes to increased risk of craniovertebral 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.
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