Download Anatomic and case review of atlanto-occipital dissociation

Anatomic and case review of atlanto-occipital dissociation
Poster No.:
C-0749
Congress:
ECR 2017
Type:
Educational Exhibit
Authors:
C. K. Ho, D. Tank, L. Woroch, E. S. Gould; Stony Brook, NY/US
Keywords:
Trauma, Education, MR, CT, Musculoskeletal spine, Emergency,
Anatomy
DOI:
10.1594/ecr2017/C-0749
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Learning objectives
At the completion of this session, participants should be able to:
1.
2.
3.
Describe the relevant anatomy of the craniocervical region.
Analyze patterns of injury and determine stability/instability.
Optimize MRI protocols for diagnosis.
Background
•Craniocervical injuries range from obvious to subtle fractures and ligamentous injuries
to that of complete atlanto-occipital (AO) dislocation.
•Recognizing these injuries is paramount to clinical care as instability can lead to
significant morbidity and mortality. Prompt diagnosis leads to earlier treatment, which
may minimize subsequent neurological deficit.
•The most common mechanism of injury has been reported to be high speed motor
vehicle accidents and pedestrians struck.
•Occipitocervical dissociation is more common among children and young adults, up to
3 times more common in children than adults.
•Considerable force is required to disrupt the atlanto-occipital (AO) junction often with
concurrent traumatic injuries to other parts of the body.
•These injuries are frequently fatal with an estimated 20-30% mortality secondary to
craniocervical dissociation.
•In severe cases, sudden death results from brainstem injury. Other injuries may be
secondary to traction or compressive mechanisms. Symptoms can indirectly occur via
ischemia.
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•With recent improvements in emergency resuscitation, cervical immobilization, and
rapid transport, there have been more reported survivors of occipitocervical dissociation
injuries.
•Emphasis must be placed on prompt and accurate diagnosis which may be clouded by
a normal neurological examination, which can occur in up to 20% of significant injuries.
•Subtle clinical and imaging findings may be missed, particularly, in patients with mild
neurological symptoms.
Findings and procedure details
1. Anatomy
Fig. 1 on page 10
The craniocervical junction (CCJ) is the transition site between the mobile cranium and
the relatively rigid spinal column as the medulla transitions to the spinal cord.
The CCJ is comprised of intricate functional relationships between the occiput, atlas, and
axis, which comprise the occipital-atlantoaxial complex.
The atlanto-occipital junction is comprised of paired synovial joints between the convex
occipital condyles and the concave surface of the opposing C1 superior articular facets. A
relatively thick fibrous capsule supports each joint. The primary motion at this articulation
is flexion and extension, which ranges up to 25 degrees with approximately 5 degrees of
axial rotation. The anterior atlanto-occipital membrane is a broad fibrous tissue extending
from the upper margin of the anterior arch of C1 to the clivus. The posterior atlantooccipital membrane is broad thin membrane connecting the posterior foramen magnum to
the posterior arch of C1. Laterally, the anterior and posterior atlanto-occipital membranes
merge with the capsular ligaments.
The atlanto-axial junction allows for axial rotation and is comprised of three synovial
joints: the paired lateral atlanto-axial synovial joints and the medial atlanto-axial joint. The
paired lateral atlanto-axial joints lie between the articular facets of the lateral masses
of C1 and C2. Thin fibrous capsules provide minimal support. The medial atlanto-axial
joint (atlanto-dental joint) is a synovial pivot joint which lies anterior and posterior to the
Page 3 of 40
odontoid process of C2. The anterior portion of the medial joint lies between the anterior
arch of C1 and the odontoid process. The posterior portion of the medial joint lies between
the odontoid process and the transverse ligament of atlas.
There are six synovial lined articulations allowing for rotation of C1 and C2:
•
•
•
Paired occipito-atlantal joints
Anterior and posterior median atlantoaxial joints
Paired lateral atlantoaxial joints
Numerous supporting ligaments surround these joints and can be divided based on their
number of attachments. The following have 3 bony attachments:
•
•
•
Anterior longitudinal ligament
Cruciform ligament of the atlas
Tectorial membrane
The following have 2 bony attachments:
•
•
•
•
•
Anterior and posterior atlanto-occipital membranes
Atlantoaxial ligament
Apical ligament of the dens
Alar ligaments
Atlantoaxial membrane
The critical structures that have been shown to maintain craniocervical stability are the
following:
•
•
•
Alar ligaments
Transverse fibers of the cruciate ligament of the atlas
Tectorial membrane
Primary Stabilizers - Alar Ligaments
•
•
•
•
The paired alar ligaments are comprised of strong, thick bands extending
from the posterolateral surface of the dens to the occipital condyles.
Their function is to limit rotation at the atlantoaxial joint, flexion at the atlantooccipital joint, and lateral bending.
The alar ligaments work in conjunction with the tectorial membrane in
limiting flexion.
This is can be seen in all three imaging planes.
Fig. 2 on page 11
Primary Stabilizers - Cruciate Ligament of the Atlas
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•
The cruciate ligament of the atlas is comprised of three parts:
1.
2.
3.
Transverse ligament
Superior longitudinal band
Inferior longitudinal band
•
Structurally it is considered the strongest ligament of the craniocervical
junction and serves as a primary stabilizing ligament as it anchors the
odontoid process of the axis to the atlas.
The superior longitudinal band extends cranially to attach to the occiput,
while its inferior longitudinal band extends caudally to the body of C2.
The transverse ligament of the atlas forms a fibro-osseous ring around the
odontoid process, as it attaches to the medial aspects of the lateral masses
of C1.
The horizontal component is best seen in the axial and coronal MR planes.
The vertical components may be seen in the sagittal and coronal planes.
•
•
•
Fig. 3 on page 11
Primary Stabilizers - Tectorial Membrane
•
•
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•
The tectorial membrane is a strong band of longitudinally oriented fibers
extending from the occipital bone to the dorsal surfaces of the C2 and C3
vertebral bodies.
Cranially, it blends with the periosteal layer of the dura. Caudally, it extends
as the posterior longitudinal ligament.
It serves to restrict extension, flexion, and vertical translation.
This is best seen in the sagittal plane.
Fig. 4 on page 12
Secondary Stabilizers
Apical ligament
•
•
The apical ligament is a thin fibrous remnant of the notochord surrounded
by fatty tissue extending from the apex of the dens to anterior margin of the
basiocciput.
This may be absent in up to 20% of patients.
Fig. 5 on page 14
Anterior atlanto-occipital membrane
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•
The anterior atlanto-occipital membrane extends from the occipital bone to
the anterior arch of C1.
Fig. 6 on page 16
Posterior atlanto-occipital membrane
•
•
•
•
The posterior atlanto-occipital membrane extends from the posterior margin
of the foramen magnum to the posterior arch of C1.
Caudally it continues as the ligamentum flavum. At the foramen magnum it
consists of the occipital periosteum.
Normal defects within it allow for passage of the vertebral arteries and
suboccipital nerves.
Laterally both of these membranes coalesce with the capsular ligaments.
Fig. 7 on page 18
Anterior atlanto-axial ligament
•
The anterior atlanto-axial ligament connects the inferior aspect of the
anterior C1 arch to the anterior aspect of the body of C2.
Fig. 8 on page 18
Posterior atlanto-axial ligament
•
The posterior atlanto-axial ligament onnects the inferior aspect of the
posterior C1 arch to the posterior element of C2.
Fig. 9 on page 20
2. Imaging Protocols
Initial evaluation of cervical injuries often begins with conventional radiography depending
on injury severity. However, in the case of severe acute trauma or if there is any suspicion
for cervical spine injury, CT is the modality of choice. MRI is preferred for evaluation of
the ligamentous structures as well as for assessing injury to the spinal cord.
In the setting of trauma, when radiographs are performed, the protocol usually includes
AP, lateral, and open mouth views (odontoid views). A swimmer's lateral view may also
be performed, as necessary, to assess the lower cervical spine. More limited examination
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may be performed for specific indications. Flexion and extension lateral views may also
be obtained to assess for cervical instability.
Removal of the cervical collar is not performed by radiology in the acute setting.
CT imaging may include a myelogram.
MR imaging of the cervical spine should include basic T1, T2, and STIR sequences. At
our institution, this includes sagittal T1, sagittal STIR, and axial T2 sequences. In addition,
for more reliable visualization of the ligaments, high resolution proton density images in
the coronal and sagittal planes are also obtained without fat saturation.
3. Normal Measurements
The basion-dens interval (BDI), evaluated in the midsagittal plane, is measured
between the inferior-most tip of the basion and the closest point of the odontoid process.
This distance should be <8.5 mm on CT and <12mm on radiographs.
Fig. 10 on page 22
The basion-posterior axial line (BAI), evaluated in the midsagittal plane, is measured
between the basion and a line superiorly extending from the posterior cortical margin
of the body of the axis. On radiographs, this distance should be <12 mm. On CT, this
distance can range from -8.7 to 26 mm, and is not a reliable measurement.
Fig. 11 on page 24
The Powers Ratio, evaluated in the midsagittal plane, is a ratio of the distance between
the tip of the basion to the spinolaminar line and the distance between the opisthion to the
midpoint of the posterior aspect of the anterior arch of C1. The normal value is considered
0.9. If the ratio >1, there is increased suspicion for anterior atlanto-occipital dissociation.
If the ratio <0.9, there is increased suspicion for posterior atlanto-occipital dissociation,
odontoid fractures, and C1 ring fractures.
Fig. 12 on page 24
The atlanto-dental interval (ADI), evaluated in the midsagittal plane, is measured
between the posterior aspect of the anterior arch of C1 at its craniocaudal midpoint to
the anterior aspect of the dens. On radiographs this measures <2 mm in adults and <5
mm in pediatric patients.
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•
•
•
>3-6 mm, suspicious for transverse ligament injury
>6 mm, suspicious for alar ligament injury
>9 mm, indicates increased risk of neurologic injury for which surgical
stabilization recommended
Fig. 13 on page 25
The posterior atlanto-dental interval (PADI), evaluated in the midsagittal plane, is
measured between the anterior aspect of the posterior arch of C1 at its craniocaudal
midpoint and the posterior aspect of the dens. This estimates the size of the spinal canal
on CT, normally 17-29 mm. A measurement <14 mm accurately predicts spinal cord
compression / impending neurologic deficit. This requires surgical stabilization.
Fig. 14 on page 27
4. Grading
Harborview classification
Stage 1
•
•
•
MR evidence of osseoligamentous stabilizer injury
Craniocervical alignment within 2 mm of normal
Distraction of =<2 mm on traction radiography
Stage 2
•
•
•
MR evidence of osseoligamentous stabilizer injury
Craniocervical alignement within 2 mm of normal
Distraction of >2 mm on traction radiography
Stage 3
•
Craniocervical malalignment >2 mm on static radiography
There are variations in determining surgical treatment. Some have suggested that
more than one abnormal measurement (BDI, BAI, Powers Ratio, ADI, PADI) or gross
abnormality in the occipito-atlantal joint, alar ligaments, cruciate ligaments, or tectorial
membrane requires surgical intervention.
5. Cases
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Selected review of cases demonstrates examples ranging from abnormal measurements
and subtle ligamentous injury to significant atlanto-occipital dissociation with inferior
cerebellar herniation.
Case 1
Fig. 15 on page 29
A 16 year old girl presents after a high speed motor vehicle crash into a pole. The patient
was restrained at impact. She presents with neck and shoulder pain with no neurologic
deficits.
Initial CT imaging demonstrated no significant abnormality. However, subsequent MR
demonstrates complete tear of the left alar ligament.
Case 2
Fig. 16 on page 29 Fig. 17 on page 31
An 18 year old man was found down on the street after being struck by a motor vehicle.
The patient had extensive trauma involving the face and pelvis and experienced cardiac
arrest.
Initial CT demonstrated a minimally increased basion-dens interval. A punctate osseous
fragment was seen at the anterior craniocervical junction. Subsequent MRI confirmed
unstable soft tissue injury, which included, complete tear of the tectorial membrane,
complete tear of the left alar ligament, and high grade sprain of the right alar ligament.
Case 3
Fig. 18 on page 31 Fig. 19 on page 32
A 25 year old male unrestrained driver was involved in a high speed motor vehicle crash
into a tree. He was under the influence of alcohol. The patient additionally had scapular
and thoracic spine fractures.
Initial CT demonstrated significant prevertebral soft tissue emphysema and edema
in addition to pneumocephalus, suggesting craniocervical injury. Craniocervical
measurements were within normal limits, but the dens demonstrated abnormal relation to
the lateral masses. Subsequent MRI demonstrated avulsion of the right alar ligament and
complete tears of the apical ligament and tectorial membrane, amounting to an unstable
pattern of injury.
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Case 4
Fig. 20 on page 33
A 26 year old man was struck by a motor vehicle while crossing the street. The patient
had concomitant intracranial hemorrhage.
Initial CT demonstrated no significant abnormality. Subsequent MRI demonstrated partial
tears of the tectorial membrane.
Case 5
Fig. 21 on page 35
A 42 year old man presented after being ejected from his vehicle after motor vehicle
accident. The patient was unresponsive at the scene.
Initial CT demonstrated no significant abnormality. Subsequent MRI demonstrated minor
sprain of the transverse component of the cruciate ligament of the atlas.
Case 6
Fig. 22 on page 37
A 52 year old man was struck by a motor vehicle while riding a motorized lawn mower.
A few days after admission, the patient expired from anoxic brain injury and cerebral
herniation.
Initial CT of the cervical spine demonstrates dramatic derangement of the normal
craniocervical measurements, compatible with severe injury and craniocervical
dissociation.
Images for this section:
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Fig. 1: Cervical spine. Coronal, sagittal, and axial proton density MR images demonstrate
normal osseous anatomy of the cervical spine. Lateral masses of C1 (red arrows), Dens
(yellow arrow), Anterior arch of C1 (blue arrow), Clivus (orange arrow).
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Fig. 2: Cervical spine. Coronal and axial proton density MR images demonstrate the
alar ligaments (red arrows). Sagittal proton density MR image demonstrates the left alar
ligament (yellow arrow).
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Page 11 of 40
Fig. 3: Cervical spine. Consecutive coronal proton density MR images demonstrate the
transverse component of the cruciate ligament of atlas (red arrows) A few longitudinal
fibers can be seen forming its cruciform shape. Axial proton density MR image
demonstrates the transverse component of the cruciate ligament, a primary stabilizer of
the craniocervical junction. Sagittal proton density MR image demonstrates the superior
longitudinal fibers of the cruciate ligament of atlas (yellow arrow).
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
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Fig. 4: Cervical spine. Sagittal proton density MR image demonstrates the tectorial
membrane (red arrow). A few longitudinal fibers of the cruciate ligament of the atlas can
be seen just anterior.
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Page 14 of 40
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Fig. 5: Cervical spine. Sagittal proton density MR image demonstrates the apical ligament
(red arrow).
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
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Fig. 6: Cervical spine. Sagittal proton density MR image demonstrates the anterior
occipito-atlantal membrane (red arrow).
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Fig. 7: Cervical spine. Coronal proton density MR image demonstrates the posterior
occipito-atlantal membranes bilaterally (red arrows). An image in the sagittal plane also
demonstrates the posterior occipito-atlantal membrane (red arrow).
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Page 18 of 40
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Fig. 8: Cervical spine. Sagittal proton density MR image demonstrates the anterior
atlanto-axial ligament (red arrow).
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
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Fig. 9: Cervical spine. Sagittal proton density MR image demonstrates the posterior
atlanto-axial ligament (red arrow).
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
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Fig. 10: Cervical spine. Noncontrast CT in the midsagittal plane demonstrates a normal
basion-dens interval (BDI) indicated by the orange line.
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Fig. 11: Cervical spine. Noncontrast CT in the midsagittal plane demonstrates a normal
basion-posterior axial line interval (BAI) indicated by the horizontal orange line.
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Page 24 of 40
Fig. 12: Cervical spine. Noncontrast CT in the midsagittal plane demonstrates the proper
locations to measure the Powers Ratio indicated by the orange lines. Specifically these
are lines between the tip of the basion to the spinolaminar line and between the opisthion
to the midpoint of the posterior aspect of the anterior arch of C1.
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Page 25 of 40
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Fig. 13: Cervical spine. Noncontrast CT in the midsagittal plane demonstrates a normal
atlanto-dental interval (ADI) indicated by the orange line.
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Page 27 of 40
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Fig. 14: Cervical spine. Noncontrast CT in the midsagittal plane demonstrates a normal
posterior atlanto-dental interval (PADI) indicated by the orange line.
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Fig. 15: Cervical spine. Sagittal proton density MR image demonstrates abrupt
nonvisualization of the left alar ligament (red arrow), compatible with complete tear.
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Page 29 of 40
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Fig. 16: Cervical spine. Sagittal CT demonstrates a bone fragment superior to the anterior
arch of C1 (blue arrow) as well as a basion-dens interval measuring between 10-11 mm
(normal <9 mm).
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Fig. 17: Cervical spine. Coronal and axial proton density MR images demonstrate
disorganized and indistinct fibers of the left alar ligament compatible with complete tear
(blue arrow). The right alar ligament demonstrates hyperintense intrasubstance signal
with a few fibers compatible with high grade sprain (red arrow). Sagittal MR image
demonstrates disruption of the tectorial membrane compatible with complete tear (yellow
arrow).
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Page 31 of 40
Fig. 18: Cervical spine. Coronal CT demonstrates asymmetry of the dens in relation
to the lateral masses (blue arrow). Extensive soft tissue gas is seen as well. Sagittal
CT demonstrates normal basion-dens and basion-posterior axial line interval. Extensive
prevertebral soft tissue swelling (yellow arrow) as well as pneumocephalus is shown (red
arrow).
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Page 32 of 40
Fig. 19: Cervical spine. Coronal and Sagittal PD MR images show avulsion of the right
alar ligament (red arrow). Additional sagittal MR image shows disruption of the apical
and superior fibers of the cruciate ligament of the atlas as well as the tectorial membrane
compatible with complete tear (blue arrow).
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Page 33 of 40
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Fig. 20: Cervical spine. Sagittal PD MR Image shows thinning and increased signal within
the tectorial membrane, compatible with partial tear (red arrow).
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
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Fig. 21: Cervical spine. Axial PD MR Image shows subtle increased intrasubstance signal
within the transverse component of the atlantoaxial cruciate ligament compatible with
minor sprain (red arrow).
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Fig. 22: Cervical spine. Sagittal CT images demonstrate an increased basion dens
interval of 36 mm, increased basion-posterior axial line interval of 23 mm, increased
atlanto-dental interval of 5 mm, and decreased posterior atlanto-dental interval of 13 mm.
There is extensive soft tissue swelling.
© Radiology, SUNY Stony Brook, Stony Brook University Hospital - Stony Brook/US
Page 37 of 40
Conclusion
•With improved emergent treatments and resuscitative techniques more patients are
surviving high impact injuries.
•Survivors of these high impact injuries or those who have previously succumbed to their
injuries often have co-existent high cervical spine injuries, which when subtle, often are
undetected.
•With increasing survival, more patients will require treatment for high cervical injuries.
It is imperative that we, as radiologists, diagnose these injuries to prevent devastating
consequences.
•Understanding the regional anatomy and normal relationships of the craniocervical
region is critical in the detection of subtle injuries in the acute trauma patient.
•Tailoring of MRI protocols greatly aids in visualizing these critical structures and should
be considered in all patients involved in high velocity injuries.
•Review of subtle and obvious abnormalities will prepare the emergency radiologist to
make a timely, accurate, and confident diagnosis.
Personal information
Corey K Ho, MD
•
•
•
Musculoskeletal Imaging Fellow, PGY-6
Stony Brook University Hospital
Stony Brook Medicine-Stony Brook, NY USA
Dharmesh R Tank, MD
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•
•
Radiology Resident, PGY-3
Stony Brook University Hospital
Stony Brook Medicine-Stony Brook, NY USA
Luboslav Woroch, DO
Page 38 of 40
•
•
•
Assistant Professor of Radiology
Stony Brook University Hospital
Stony Brook Medicine-Stony Brook, NY USA
Elaine S Gould, MD FACR
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•
•
Professor of Radiology & Orthopedic Surgery
Stony Brook University Hospital
Stony Brook Medicine-Stony Brook, NY USA
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