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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_6009_Библиотеки_им_академика_М_И_Перельмана.pdf
Atlantooccipital Dislocation
KEY FACTS
TERMINOLOGY
Trauma
• Disruption of stabilizing ligaments between occiput and C1
IMAGING
• Widened prevertebral soft tissues (nonspecific)
• Condylar sum > 4.2 mm has 100% sensitivity, 69%
specificity, and 76% accuracy
• Increased basion-dens interval (BDI) distance > 8.5 mm (CT
in adults)
• Widened unilateral atlantooccipital interval > 2 mm
○ Widened, fluid-filled facet joints between condyles and
C1
• STIR/T2WI MR best show ligamentous injury
TOP DIFFERENTIAL DIAGNOSES
• Occipital condyle fracture
• C1 Jefferson fracture
• Odontoid fracture
• Rheumatoid arthritis, adult
(Left) Sagittal graphic depicts
fatal atlantooccipital
dissociation with cord
transection ſt at the
craniocervical junction.
Stretch injury to the spinal
cord may occur, resulting in
neurologic dysfunction. (Right)
Sagittal T2WI MR exhibits
extensive abnormality with
thinning and irregularity of
the tectorial membrane .
The anterior atlantooccipital
membrane is irregular and
stretched anteriorly ſt.
Abnormal soft tissue in the
supraodontoid space st
suggests injury to the apical &
alar ligaments.
PATHOLOGY
• High-speed motor vehicle accident
• Associated injuries
○ Brainstem and cranial nerve injury
○ Fractures of occipital condyles, C1 and C2
CLINICAL ISSUES
• < 1% of acute cervical spine injuries
• Often immediately fatal; however, may have good
outcome with recognition and fixation
DIAGNOSTIC CHECKLIST
• No imaging sign 100% sensitive
• Condylar sum > 4.2 mm most sensitive CT sign of
atlantooccipital dislocation
• Powers ratio not recommended (has low sensitivity and
specificity)
• Detection of subarachnoid hemorrhage at craniocervical
junction should direct search for atlantooccipital injuries
160
(Left) Sagittal CT
reconstruction illustrates an
increase in the basion-dens
interval (BDI) ſt. The normal
distance by CT is ≤ 8.5 mm in
adults, or 12 mm on lateral
radiographs. (Right) Sagittal
CT in a soft tissue algorithm
exhibits hyperdense blood
products in the ventral
epidural space ſt. Abnormal
soft tissue is also observed in
the supraodontoid space ,
compatible with hemorrhage
along the ligaments. Rupture
of both the tectorial
membrane and alar ligament
are necessary for AOD to
occur.
Atlantooccipital Dislocation
TERMINOLOGY
Abbreviations
• Atlantooccipital dislocation (AOD)
Definitions
• Disruption of stabilizing ligaments between occiput and C1
± between C1 and C2
IMAGING
General Features
• Best diagnostic clue
○ Widening between occipital condyles and C1
○ Increased distance between basion and dens
• Location
○ Axial distraction across craniocervical junction (CCJ) can
produce either atlantooccipital or atlantoaxial dislocation
CT Findings
• Widened unilateral atlantooccipital interval > 2 mm
○ Normal range 0.5-1.8 mm in adults (wider in children)
– 1.4 mm (max for 97.5% of population)
○ Condylar sum > 4.2 mm has 100% sensitivity, 69%
specificity, and 76% accuracy
• Midline occiput to C1 spinolaminar line > 4.2 mm
○ May be artifactually shortened due to extension
positioning in collar
• Basion-dens interval (BDI) range 1.4-9.1 mm
○ Normal < 8.5 mm (max for 97.5% of population) in adults
• Anterior or posterior position of C1 relative to basion
○ Incongruity of occiput-C1 facet joints well seen on
sagittal images
• Avulsion fracture of occipital condyle or anterior arch of C1
• Subarachnoid hemorrhage at CCJ is associated with AOD, &
its detection should direct search for atlantooccipital
injuries
MR Findings
• STIR, T2WI best shows ligamentous injury
○ Tectorial membrane disruption seen in 71% of 1 series of
16 pediatric patients
○ Nonvisualization of apical, alar, and anterior atlantoaxial
ligaments
• Widened, fluid-filled facet joints between condyle and C1 >
2 mm
○ May be unilateral
• Vertebral artery injury
• Prevertebral hematoma
Imaging Recommendations
• Best imaging tool
○ CT useful for rapid triage
○ MR better shows extent of ligament injury
DIFFERENTIAL DIAGNOSIS
Occipital Condyle Fracture
• Condyle avulsions may be associated with AOD
Jefferson Fracture of C1
• Often see lateral displacement of C1 lateral masses
Odontoid C2 Fracture
• Type 2 odontoid fracture often results in posterior
displacement of dens
Atlantoaxial Rotatory Fixation
• Occiput-C1 facet joints and atlantodental interval are
normal
Rheumatoid Arthritis, Adult
• Nontraumatic atlantooccipital instability
○ Pannus destabilizes joints and ligaments
PATHOLOGY
General Features
• Etiology
○ High-speed motor vehicle accident
Staging, Grading, & Classification
• Longitudinal AOD
○ Vertical displacement
• Anterior AOD
○ Skull positioned anterior to C1
• Posterior AOD
○ Skull positioned posterior to C1
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ Respiratory failure, cranial nerve and motor deficits
○ 20% have no neurological deficit, need high index of
suspicion
Demographics
• Age
○ More common in children
– Due to relatively large head, horizontal orientation of
condyles
• Epidemiology
○ < 1% of acute cervical spine injuries
Natural History & Prognosis
• Often immediately fatal
○ However, with recognition and fixation may have good
outcome
• Poor outcomes if basion-dens distance ≥ 16 mm
Treatment
• Occiput to C2 fusion required
DIAGNOSTIC CHECKLIST
Consider
• No imaging sign 100% sensitive
• Condylar sum > 4.2 mm most sensitive CT sign of AOD
• All patients with upper cervical prevertebral soft tissue
swelling should undergo CT scan
SELECTED REFERENCES
1. Theodore N et al: The diagnosis and management of traumatic atlanto-
occipital dislocation injuries. Neurosurgery. 72 Suppl 2():114-26, 2013
2. Chaput CD et al: Defining and detecting missed ligamentous injuries of the
occipitocervical complex. Spine (Phila Pa 1976). 36(9):709-14, 2011
Trauma
161
Ligamentous Injury
KEY FACTS
IMAGING
Trauma
• Conventional radiographs insensitive to ligamentous injury
• CT: Ligamentous disruption may be inferred with varying
degrees of success by observing disruption of normal
vertebral alignment
• Best imaging method is T2W FS or STIR MR
○ Abnormal T2 hyperintensity or gross discontinuity of
spinal ligamentous structure
• Flexion-extension films: Segmental instability
○ > 3.5-mm subluxation
• STIR and T2WI FS to evaluate spinal ligamentous injury
○ Normal ligament should be thin, contiguous, and low in
signal intensity on both T1 and T2WI
○ Increased signal within ligamentous structure indicative
of edema, hemorrhage, or inflammation (stretch injury,
strain, partial tear)
○ Complete discontinuity of ligamentous structure on
T2WI indicative of disruption
(Left) Sagittal STIR MR shows
atlantooccipital dislocation
with disruption of the tectoral
membrane & alar ligaments
ſt & extensive disruption &
edema of posterior
interspinous ligaments .
Note cord compression due to
cranial dislocation st. (Right)
Sagittal T2 MR of cervical
hyperflexion-distraction injury
shows hyperintensity of the
interspinous ligament &
disruption of both the
ligamentum flavum ſt &
posterior longitudinal
ligament (PLL) st. Thickening
& increased signal are seen in
prevertebral soft tissues.
PATHOLOGY
• Forced motion of vertebral segment beyond limits of tissue
elasticity
• Associated abnormalities
○ Spinal instability
○ Traumatic disc herniation
○ Vertebral fractures
CLINICAL ISSUES
• Spinal instability predisposing to progressive deformity or
to impingement on spinal cord, nerve roots
○ Instantaneous (instability immediately following injury)
○ Delayed (> 20 days after injury)
DIAGNOSTIC CHECKLIST
• Ventral ligamentous injury of cervical spine without
fracture is rare (< 0.7%)
162
(Left) Sagittal STIR MR shows
disruption of the anterior
longitudinal ligament ſt and
PLL as well as posterior
displacement of the ventral
dural margin st due to
epidural hemorrhage. Cord
contusion is also present as
increased cord signal .
(Right) Axial T2* GRE MR at
the C1 arch level shows
increased signal to the right of
the midline in the transverse
ligament ſt due to disruption
with mild asymmetric
widening of the right denslateral mass interval .
Occipital Condyle Fracture
KEY FACTS
Trauma
TERMINOLOGY
• Bony disruption of occipital condyle
IMAGING
• Linear, comminuted, or avulsion-type fracture
○ Radiography insensitive
○ CT: Lucency in occipital condyle ± displaced fragment
○ MR: Marrow edema on T1, STIR MR
– Prevertebral or nuchal ligament edema
TOP DIFFERENTIAL DIAGNOSES
• Accessory ossification center(s)
• Osteomyelitis
• Primary or secondary skull base neoplasm
• Rheumatoid arthritis
PATHOLOGY
• High-energy blunt trauma, most often motor vehicle
accident
• Anderson & Montesano classification (1988)
○ Type I: Comminuted condylar fracture without
displacement (uncommon)
○ Type II: Extension of linear basilar skull fracture
○ Type III: Avulsion of inferomedial condyle (most common
type 75%)
CLINICAL ISSUES
• Presenting symptoms usually related to severity of head
injury
○ Most patients have mild/moderate ↓ GCS due to
intracranial injury
○ Head injury is main determinant of outcomes
• CN deficit(s) (up to 30%)
• Spasmodic torticollis from concomitant atlantoaxial
rotatory fixation
DIAGNOSTIC CHECKLIST
• Easy fracture to overlook in severely injured trauma
patients
(Left) Axial bone CT shows a
mildly displaced fracture of
the right occipital condyle
with cortical break ſt and
medial movement of the
fracture fragment. (Right)
Coronal reformatted bone CT
in the same patient shows a
lucent fracture line ſt with
minimal displacement.
Articulation with C1 is
preserved .
(Left) Sagittal STIR MR shows
hyperintense signal through a
horizontal fracture of the
occipital condyle. Signal in the
adjacent marrow spaces is
normal. (Right) Axial bone CT
shows a nondisplaced left
occipital condyle fracture ſt
as involvement from a skull
base fracture . Note the
normal C0-1 joint space
appearance .
163
Jefferson C1 Fracture
KEY FACTS
TERMINOLOGY
Trauma
• Fracture(s) of C1 ring
IMAGING
• Multiple fractures of C1 arch (2-, 3-, and 4-part fractures)
• Combined offset of lateral masses of C1 relative to lateral
margins of C2 ≥ 7 mm suggests interruption of transverse
ligament
• Avulsion fragment off inner C1 pillar at insertion of
transverse ligament indicates unstable fracture
• Widening of atlantoaxial interval
○ ≥ 4 mm concerning for interruption of transverse
ligament
○ ≥ 7 mm presumed interruption of transverse ligament
• Associated C2 fracture (hangman's fracture, odontoid
fracture)
○ Fractures at lower levels not uncommon
• May see T2 hyperintense edema if cord contusion present
(Left) Lateral radiograph of
the craniovertebral junction
shows faint lucencies in the
posterior arch of C1. (Right)
Coronal radiograph, in which
the interval between the dens
and the lateral masses of C1 is
obscured by the occipital
bone, shows lateral
displacement of the outer
margins ſt relative to C2.
TOP DIFFERENTIAL DIAGNOSES
• Congenital variants, clefts, malformations of atlas
• Rotational malalignment of atlas, axis pillars
• Pseudospread of atlas in children
PATHOLOGY
• Force transmitted down through occipital condyles onto
sloped C1 pillars with head and neck rigidly erect
• Transverse ligament often intact
• If transverse ligament is interrupted, stability of fracture
depends on integrity of alar ligaments
CLINICAL ISSUES
• Neurologic signs uncommon unless unstable fracture, injury
at another level, or vascular injury
DIAGNOSTIC CHECKLIST
• Important to evaluate lower levels for additional fractures
164
(Left) Axial NECT shows
fractures st extending
through the anterior and
posterior arches of C1. A small
bony fragment demonstrates
the site of an avulsion fracture
ſt at the attachment of the
transverse ligament. (Right)
Coronal reformatted CT shows
lateral displacement of both
C1 lateral masses ſt relative
to the occipital condyles and
C2 lateral masses. Also seen is
a bony fragment due to
transverse ligament tubercle
avulsion st.
Jefferson C1 Fracture
Trauma
IMAGING
General Features
• Best diagnostic clue
○ Lateral displacement of both articular masses of C1
relative to margins of C2 on open mouth radiograph
Radiographic Findings
• Radiography
○ Bony defects of C1
○ Widening of distance between odontoid and C1 lateral
masses on open mouth view
– Normal rotation may produce apparent offset of pilar,
simulating fracture
– Combined offset of lateral masses of C1 relative to
lateral margins of C2 ≥ 7 mm suggests interruption of
transverse ligament
□ Potentially unstable fracture
Fluoroscopic Findings
• Subluxation if unstable
CT Findings
• NECT
○ Axial CT defines components of fracture to best
advantage
○ May demonstrate various patterns of arch disruption;
may demonstrate hyperdensity in epidural space if
• CTA
○ Loss of vertebral artery integrity if vertebrobasilar
vascular syndrome present
MR Findings
• T1WI
○ Prevertebral soft tissue swelling anterior to C1;
disruption of cortical margins of C1
• T2WI
○ Edema in prevertebral soft tissues
○ May see hyperintense cord edema if contusion is present
• MRA
○ Vertebral artery injury, if present, with dissection or
occlusion
Angiographic Findings
• Useful if CTA/MRA equivocal or for persistent concern for
vertebral artery injury; endovascular intervention
Imaging Recommendations
• Best imaging tool
○ Unenhanced multidetector CT scan
• Protocol advice
○ Any lateral spread of C1 pillars on open mouth x-ray view
requires CT
○ Thin-slice (≤ 1 mm) axial CT in bone reconstruction
algorithm
○ Evaluate entire cervical spine as well as upper thoracic
spine
○ Axial and sagittal T1WI and T2WI, sagittal STIR to
evaluate fracture morphology, displacement,
ligamentous injury, soft tissue edema
DIFFERENTIAL DIAGNOSIS
Congenital Variants, Clefts, Malformations of Atlas
• May show 1-2 mm offset of C1 pillars from those of C2
• Various deficiencies of arch development can be seen
• Most are partial hemiaplasias of posterior arch
• Clefts, congenital defects show smooth or well-corticated
edges
Rotational Malalignment of Atlas, Axis Pillars
• Generally seen unilaterally, with rotation and abduction of
head
Pseudospread of Atlas in Children
• Common finding in children 3 months to 4 years of age
evaluated for minor trauma
• Caused by disparity in growth rates of atlas and axis
PATHOLOGY
General Features
• Etiology
○ Axial compressive force applied to skull vertex
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ Upper neck pain after compression trauma (e.g., diving);
cervical muscle spasm; limited range of motion; head tilt
• Clinical profile
○ Trauma victim; upper neck pain
Natural History & Prognosis
• Stable fracture
○ Healing with conservative therapy in majority of cases
Treatment
• Nondisplaced isolated anterior or posterior atlas arch
fractures and fractures of atlas lateral mass
○ External cervical immobilization; rigid collars, suboccipital
mandibular immobilizer braces, and halo ring-vest
orthoses; 8-12 weeks; 96% rate of healing
• Combined anterior and posterior arch fractures of atlas
with intact transverse ligament
○ Rigid collar, suboccipital mandibular immobilizer brace,
or halo orthosis; 10-12 weeks
• Combined anterior and posterior arch fractures of the atlas
with transverse ligament disruption; halo orthosis for 12
weeks or surgical stabilization and fusion
DIAGNOSTIC CHECKLIST
Consider
• Routine CT of cervical spine in trauma victims with severe
neck pain
• Evaluate for extension of fracture into foramina
transversarium
Image Interpretation Pearls
• Well-corticated edges of midline C1 arch defects are likely
congenital clefts
• 1-2 mm offset of C1 lateral masses vs. C2 on open mouth
view in infants may be normal variant
165
Atlantoaxial Rotatory Fixation
KEY FACTS
IMAGING
Trauma
• Abnormal rotatory motion of C1 with respect to C2 defined
by 3-position CT scan
TOP DIFFERENTIAL DIAGNOSES
• Etiologies of atlantoaxial rotatory fixation (AARF)
○ Trauma
○ Nasopharyngeal infection (Grisel syndrome)
○ Prior head and neck surgery
PATHOLOGY
• Pang type I AARF: Unaltered or locked C1-C2 coupled
configuration regardless of corrective counter-rotation
• Pang type II AARF: Reduced C1-C2 separation angle with
forced correction but C1 does not cross C2
• Pang type III AARF: Show C1-C2 crossover but only with
head turned far to opposite side
(Left) Fielding-Hawkins
classification of atlantoaxial
fixation shows type I rotatory
displacement of C1 without
ligamentous abnormality; type
II 3- to 5-mm anterior
displacement of C1; type III
shows > 5-mm anterior
displacement associated with
deficiency of transverse
ligament; type IV shows C1
displacement posteriorly.
(Right) In Fielding-Hawkins
type I fixation, radiograph
shows rotation of head to the
left. Note typical appearance
of rotated C1 applied to left
side of C1 with widening of
right C1-C2 spacing .
CLINICAL ISSUES
• Persistently rotated head that is painful during attempts at
correction (painful torticollis)
• Head typically laterally flexed on side opposite to pointing
chin (cock-robin appearance)
• Treatment in acute phase gives best outcome (Pang type IIII)
DIAGNOSTIC CHECKLIST
• Fielding-Hawkins type III, IV involve traumatic rupture of
transverse atlantal and other stabilizing ligaments
○ Emergent and serious injuries require immediate surgical
intervention to protect cord
○ These more serious injuries are separate from pure
rotatory fixations, which are never acutely unstable (as in
Pang type I-III AARF)
166
(Left) Fielding-Hawkins type I
atlantoaxial rotatory fixation
on this 3D CT reconstruction
nicely visualizes the markedly
left rotated C1 ſt with
respect to the mildly rotated
C2 . (Right) Fielding type I
rotatory fixation is seen on
this anterior view from a
volume-rendered CT
reconstruction showing the
morphology of the rotated C1
ſt and morphologically
normal odontoid. The axis of
rotation is about the anterior
atlantodental joint st, which
is consistent with intact
ligamentous complex.
Atlantoaxial Rotatory Fixation
TERMINOLOGY
Abbreviations
• Atlantoaxial rotatory fixation (AARF)
Synonyms
• Atlantoaxial rotatory subluxation, rotary subluxation
Definitions
• Rotatory fixation or subluxation: Persistent rotational
deformity of C1-C2 complex with resultant torticollis and
head in cock-robin position; normal atlantodental interval
(ADI)
• Rotatory dislocation: More severe injury with anterior
displacement of lateral mass of C1 relative to C2 with
widening of ADI
IMAGING
General Features
• Best diagnostic clue
○ Abnormal rotatory motion of C1 with respect to C2
defined by 3-position CT scan
Imaging Recommendations
• Protocol advice
○ 3 separate scans covering occiput to C2
– Head in presenting position, undisturbed (designated
as P position)
– Head turned to zero position by examiner (designated
as P0 position)
– Head turned to side opposite to presenting position
as far as tolerable (designated as P_ )
DIFFERENTIAL DIAGNOSIS
Etiologies of Atlantoaxial Rotatory Fixation
• Trauma
○ More severe forms caused by violent trauma
○ Frequent coexistence of fractured clavicle on opposite
side of chin
• Nasopharyngeal infection (Grisel syndrome)
○ Many purported mechanisms, including spread of
infection to CV joints; synovial inflammation
• Prior head and neck surgery
○ Head rotated or hyperextended with otopharyngeal
inflammation; general anesthesia and muscle relaxants
• Mimics
○ Muscular torticollis related to overactivity or contracture
of sternomastoid muscle on side opposite to chin
○ CV junction segmentation anomalies with instability
PATHOLOGY
Staging, Grading, & Classification
• Fielding-Hawkins (1977)
○ Type I: Rotatory fixation without anterior displacement
of atlas (displacement of < 3 mm)
– Most common type
○ Type II: Rotatory fixation with anterior displacement of
atlas from 3-5 mm
– Associated with abnormality of transverse ligament
○ Type III: Rotatory fixation with displacement > 5 mm
Trauma
– Associated with deficiency of transverse and alar
ligaments
○ Type IV: Rotatory fixation with posterior displacement
– Rare
• Pang (2005)
○ 5 distinct groups based on motion curves obtained from
3-position CT
– Does not include cases of concomitant acute
translational instabilities of C1 on C2 as in FieldingHawkins types III, IV
○ Type I AARF: Unaltered or locked C1-C2 coupled
configuration regardless of corrective counter-rotation
– Motion curve is horizontal in upper 2 quadrants of C1-
C2 motion template
○ Type II AARF: Reduced C1-C2 separation angle with
forced correction but C1 does not cross C2
– Motion curve slopes downward from right to left in
upper quadrants but does not traverse x-axis
○ Type III AARF: Shows C1-C2 crossover but only with
head turned far to opposite side
– Motion curve traverses x-axis left of C1 = -20°
○ Group IV: Normal dynamics in muscular torticollis
without injury to C1-C2 joints
○ Group V: Diagnostic gray zone
– Motion curve shows features between normal and
type III AARF
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ Persistently rotated head that is painful during attempts
at correction (painful torticollis)
○ Head typically laterally flexed on side opposite to
pointing chin (cock-robin appearance)
Demographics
• Age
○ Childhood (18 months to 18 years)
Natural History & Prognosis
• Treatment in acute phase gives best outcome (Pang type IIII)
• 1 study showed no acute patients required halo fixation or
surgical fusion with short treatment duration of < 4 months
• Subacute patients have worse outcome with longer
treatment course; many of these patients require halo
fixation
• Chronic patients have worst prognosis with Pang type I, II
AARF, with high percentage of persistent abnormal motion
requiring fusion
• Best overall outcome with Pang acute type III AARF and
worst outcome chronic type I AARF
DIAGNOSTIC CHECKLIST
Consider
• Fielding-Hawkins type III, IV involve traumatic rupture of
transverse atlantal and other stabilizing ligaments
○ Emergent and serious injuries requiring immediate
surgical intervention to protect cord
○ These more serious injuries are separate from pure
rotatory fixations, which are never acutely unstable
167
Odontoid C2 Fracture
KEY FACTS
TERMINOLOGY
Trauma
• Type I: Avulsion fracture from tip of odontoid at insertion of
alar ligament
○ Usually stable injury
○ Usually seen in conjunction with more extensive
craniocervical injury
• Type II: Transverse fracture through base of odontoid
○ Most likely to progress to nonunion without surgical
fusion
• Type III: Oblique fracture extending from base of odontoid
into body of C2
IMAGING
• Direct visualization of fracture line on radiography
○ Soft tissue swelling anterior to C2 in acute cases
○ Displacement of dens, C1 on lateral film
• CT protocol: Thin-slice (1 mm or less) multidetector CT, fast
scan time to minimize motion
○ Sagittal and coronal reformatted images mandatory
(Left) Anterior graphic shows
an avulsion fracture through
the tip of the odontoid ſt
(type I), transverse fracture at
the base of the odontoid
(type II), and an odontoid
fracture extending through
the body of C2 st (type III).
(Right) Sagittal reformatted
bone CT shows a nondisplaced
fracture ſt through the tip of
the odontoid (type I odontoid
fracture).
• MR
○ Effacement of thecal sac on MR due to displaced
fracture
○ Cord injury, if present, hyperintense on T2WI
○ Fractures without compression &/or fractures with
distraction do not reliably generate marrow edema and
can lead to false-negative MR imaging
TOP DIFFERENTIAL DIAGNOSES
• Os odontoideum
• Congenital variation: 3rd occipital condyle (condylus tertius)
• Rheumatoid arthritis: C1/C2 subluxation
• Pathologic C2 fracture
• Ossiculum terminale persistens
PATHOLOGY
• Osteoporosis in elderly predisposes to type II fracture and
nonunion
168
(Left) Sagittal reconstructed
CT shows a fracture ſt
extending through the base of
the dens (type II). The dens is
moderately displaced
anteriorly. (Right) Coronal
reformatted CT shows a type
III fracture extending from the
right of the base of the
odontoid ſt through the C2
body and into the left lateral
mass .
Odontoid C2 Fracture
TERMINOLOGY
Synonyms
• Dens fracture
Definitions
• Type I: Avulsion fracture from tip of odontoid at insertion of
alar ligament
• Type II: Transverse fracture through base of odontoid
• Type III: Oblique fracture extending from base of odontoid
into body of C2
IMAGING
General Features
• Best diagnostic clue
○ Lateral radiograph: Anterior or posterior displacement of
C1 arch vs. C2 with prevertebral soft tissue swelling
○ Fracture visible on open mouth (dens) view
Radiographic Findings
• Radiography
○ Type I: Oblique fracture fragment at rostral aspect of
odontoid on frontal view
○ Type II: Fracture line through base of odontoid
○ Type III
– Fracture line through base of odontoid extending into
C2 body
– Fracture may extend into superior articular surfaces of
C2
○ All: Swelling of prevertebral soft tissues
CT Findings
• NECT
○ Soft tissue swelling anterior to C2 in acute cases
○ Lucent fracture line through tip of odontoid (type I) or
base of odontoid (type II) ± extent into C2 body (type III)
MR Findings
• T1WI
○ Abnormal low T1 marrow signal due to osseous edema
○ Cortical disruption
○ May directly appreciate cortical defect at fracture site
○ Thickened prevertebral soft tissues
• T2WI
○ Variable and inconsistent hyperintense signal in C2
marrow due to osseous edema
○ Hyperintense soft tissue edema
○ Effacement of thecal sac due to displaced fracture
DIFFERENTIAL DIAGNOSIS
Os Odontoideum
• Odontoid replaced by ossicle with no continuity to C2 body
• Corticated margins on radiography, CT
• No soft tissue swelling
Pathologic C2 Fracture
• Can produce pathologic odontoid fracture
• Metastases, infection, other inflammatory arthritidis
Rheumatoid Arthritis: C1/C2 Subluxation
• Laxity, subluxation
Trauma
Ossiculum Terminale Persistens
• Nonfusion of ossiculum terminal (apical odontoid epiphysis)
to body of dens beyond 12 years of age
Congenital Variation: 3rd Occipital Condyle
(Condylus Tertius)
• Midline bony peg off anterior lip of foramen magnum may
articulate to dens, simulate odontoid type I fracture
PATHOLOGY
Staging, Grading, & Classification
• Anderson and D’Alonzo (1974)
○ Type I fracture: Oblique fracture through upper portion
of odontoid process
○ Type II fracture: Fracture across base of odontoid process
near junction with axis body
○ Type III fracture: Fracture that includes odontoid and
extends into axis body
• Hadley modification (1988)
○ Type IIA: Comminuted fracture of base of odontoid with
associated free fracture fragments
– Highly unstable
• Grauer modification (2005)
○ Type IIA: Minimally/nondisplaced fracture with no
comminution; treated with external immobilization
○ Type IIB: Displaced odontoid fracture that extends from
anterior-superior to posterior-inferior or transverse;
treated with anterior screw fixation if reducible
○ Type IIC: Fracture extending from anterior-inferior to
posterior-superior or with significant comminution;
considered for posterior internal fixation and fusion
CLINICAL ISSUES
Natural History & Prognosis
• Fusion produces stability
• Nonunion common in elderly without primary fusion
○ May stabilize by fibrous union with prolonged
immobilization
Treatment
• Fracture pattern dictates management
• Type I fracture
○ Usually stable injury
○ Treated with simple immobilization
• Type II fracture
○ Most likely to progress to nonunion
• Type III fracture
○ Nonunion uncommon after treatment with traction
followed by bracing
DIAGNOSTIC CHECKLIST
Consider
• STIR to show soft tissue edema in prevertebral space
(missing in chronic nonunion)
○ Marrow edema an unreliable sign for presence of
fracture in distraction injuries
• Flexion/extension films or fluoroscopy for evaluating
stability
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