OS Odontoideum

advertisement
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
Download
Related flashcards

Gynaecology

24 cards

Lymphatic system

25 cards

Animal anatomy

36 cards

Tissues (biology)

29 cards

Create Flashcards