University of Michigan Neurosurgery !
Redefining Chiari I Malformation: Prevalence and Natural History
Jennifer Strahle, M.D. Neurosurgery Resident
University of Michigan, Department of Neurosurgery
University of Michigan Neurosurgery !
No disclosures
University of Michigan Neurosurgery !
University of Michigan Neurosurgery !
Chiari Malformation (CM) Definition
Why 5mm?
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5mm definition
82 normal individuals- 20 mm above to 2.8 mm below the foramen magnum 13 CM patients- range 5.2 mm below to 17.7 mm below the foramen magnum
Aboulezz et al, 1985 Barkovich et al, 1986
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Tonsillar position vs age: Mikulis et al, 1992
n= 18 – 30 per decade
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Methods
• 62,533 consecutive subjects (48,418 adults; 14,116 pediatric) • Brain or C-spine MRI at a single institution for any
indication over 11 years • 2400 randomly selected – 300 in each decade age group
• All MRIs reviewed for tonsil height – Tonsil position determined with respect to the Basion-
Opisthion line • All records reviewed for symptoms
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Average Tonsil Position
All subjects
CM patients excluded
(n=300 per decade)
(n=22 CM pts)
Smith et al, 2013, JNS
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• Pegged morphology more likely to have tonsil position >5mm below FM vs rounded (85% vs 1.7%; p<0.0001)
• Female gender associated with lower tonsils (p<0.0001)
• Asymmetric tonsils, especially lower on right, associated with lower tonsil position (p<0.0001)
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Tonsil Position by Decade
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Tonsillar Distribution (0-10 years)
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Tonsillar Distribution (11-20 years)
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Tonsillar Distribution (21-30 years)
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Tonsillar Distribution (31-40 years)
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Tonsillar Distribution (41-50 years)
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Do these findings fit with existing data?
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Mikulis et al, 1992
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Prevalence of CM
• Brain or Cervical spine MRI at a single institution for any indication
• 48,418 adults • 14,116 pediatric patients • 11 year interval • MRI records versus patients presenting to neurosurgery
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Adult Prevalence
• 0.77% (372/48417) • Higher prevalence in females • Mean tonsil position: +8.7mm – males- 9.4 mm; females- 8.5 mm
• 32% with symptoms – HA most common – Most frequent in the 31-40 y/o age group
• 8.6% with syrinx
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Adult Prevalence 1.46
1.21
0.79
0.62
0.26 0.16
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
19-30 31-40 41-50 51-60 61-70 71+
CM
(%
)
Age
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-3
-2.5
-2
-1.5
-1
-0.5
0
0.5 0 to 10 11 to 20 21 to 30 31 to 40 41 to 50 51 to 60 61 to 70 71+
Average Tonsil Position
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-3
-2.5
-2
-1.5
-1
-0.5
0
0.5 0 to 10 11 to 20 21 to 30 31 to 40 41 to 50 51 to 60 61 to 70 71+
Average Tonsil Position
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MRI prevalence: Meadows et al, 2000
-22,591 patients -175 were found to have tonsil position > 5 mm -0.7 % CM prevalence
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Pediatric Prevalence
• 3.6 % overall • No difference
with respect to age or sex
• Average: 10.2 mm Strahle et al, 2011, JNS-Pediatrics
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CM and Syrinx
Syrinx in 117/509 patients (23%)
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CM presentation
• 68% asymptomatic at presentation
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Adult-‐ Symptoms
0
5
10
15
20
25
30
35
19-30 31-40 41-50 51-60 61-70 71+
Perc
enta
ge o
f Sym
ptom
atic
CIM
Age Groups(yrs)
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
19-30 31-40 41-50 51+
≥5
mm
(%
)
Age
Prevalence (adult): MRI for epilepsy or Trauma
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Natural History (pediatric)
• Symptomatic CM vs. incidental finding • Initial recommendation for conservative
management and at least 1 year of clinical and radiographic follow-up
• 147 patients
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CM-‐ Natural History
(Strahle et al, JNS-pediatrics, 2011)
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Natural history-‐ CM and syrinx
Length Width
20 patients (13.5%): 13 with syrinx at diagnosis; 7 with new syrinx
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Natural history: Surgery
6 with syrinx had surgery (2- surgery unrelated to syrinx)
Time to surgery: 2.1 years
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CM natural history
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CM and scoliosis
• CM is common (3.6% in pediatric patients) • Scoliosis is common (12.9% in pediatric
patients) • Is there a relationship? • Role of syrinx ?
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Etiology of scoliosis
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CM-‐scoliosis surgical series
• Most have included patients with CM, scoliosis and syrinx
• Factors associated with improvement of curve: age, PFD, degree of initial curve
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114 with CM and Scoliosis
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Natural History: 55 patients, 1 year f/u
Outcomes after PFD: 87 patients
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CM and scoliosis
For a relationship: • syrinx not associated with
progression of curve • no difference in syrinx status in
those with left thoracic curve; however average tonsil position +14.5 (vs 10.8 mm) higher in left thoracic curve
• curve progression similar for those with and without a syrinx after initial PFD
Against a relationship: • No relationship between
magnitude of curve or curve location and tonsil position or CSF flow at FM
• No difference in tonsil position in those that progressed vs those that didn’t
• Progression of curve in natural history cohort associated with age
• 43% of patients without a syrinx needed a second surgery vs 23% of those with a syrinx
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Chiari and scoliosis 13,585 patients with Brain or Cervical spine imaging
1746 with scoliosis (12.9%) 508 with Chiari I (3.7%) 258 with syrinx (1.9%)
114 with CM (6.5%) 143 with syrinx (8.1%)
Odds Ratio p value Female Sex 1.71 95% CI 1.54-1.90 p< 0.0001
Older age 1.02 95% CI 1.01-1.03 p< 0.0001
Syrinx 8.61 95% CI 6.54-11.34 p< 0.0001
Chiari 1.02 95% CI 0.79-1.32 NS
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CM-‐scoliosis-‐syrinx
• Compare CM-syrinx to idiopathic syrinx • Hypothesis: – CM associated syrinx- a result of pathologic changes
in CSF flow – Idiopathic syrinx-a different pathophysiologic
process
• 278 patients with syrinx ≥ 3mm in maximal AP diameter (cmII-mmc excluded)
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Syrinx Etiology
0
20
40
60
80
100
120
140
CM-1 CM-0 2°CM 1-5 mm Idiopathic Tethered Cord
Spinal dysraphism
Tumor Trauma Other
# of
Pat
ient
s
Associated Pathology
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Syrinx Width
0
2
4
6
8
10
12
14
CM-1 CM-0 2°CM 1-5 mm Idiopathic Tethered Cord Spinal dysraphism
Tumor Trauma
Syrin
x W
idth
Associated pathology
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Cranial Extent
0
5
10
15
20
25
CM-1 CM-0 2°CM 1-5 mm Idiopathic Tethered Cord Spinal dysraphism
Tumor Trauma
Cran
ial E
xten
t (Le
vels
from
FM
)
Associated Pathology
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% Scoliosis
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
CM-1 2°CM Idiopathic Tethered Cord Spinal dysraphism Tumor
% s
colio
sis
Associated Pathology
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Limitations
• Detection bias for CM • Tonsil position may be influenced by other
factors • Indications for imaging vary by age • Imaging cohort not population cohort
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Conclusions
• Prevalence of Chiari varies by age
– Prevalence estimates must take age into consideration – “Normal” varies substantially by age and should be expected
to change during an individuals lifetime
– In general, tonsils are lowest during the 2nd through 4th decades
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Conclusions
• Cerebellar tonsil position, like most morphometric measurements, follows a normal distribution
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Conclusions
• Tonsil position >5 mm below the foramen magnum should not be considered a cut-point with definite pathological implications
• Tonsil position <5mm below the foramen magnum is the low end of the normal distribution that is associated with symptoms in some individuals
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Conclusions
• CM is a common (often incidental) finding in those undergoing MRI
• The natural history of CM is those selected for conservative management is generally benign
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Conclusions
• In most cases, it is unlikely that CM causes scoliosis when a syrinx is not present
• Syrinx morphology differs by etiology
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Acknowledgements
Brandon Smith, MD Cormac Maher, MD Hugh Garton, MD
Karin Muraszko, MD