redeﬁning(chiariimalformation:( …• female gender associated with lower tonsils (p

University of Michigan Neurosurgery !

Redefining Chiari I Malformation: Prevalence and Natural History

Jennifer Strahle, M.D. Neurosurgery Resident

University of Michigan, Department of Neurosurgery


No disclosures


Chiari Malformation (CM) Definition

Why 5mm?


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


Tonsillar position vs age: Mikulis et al, 1992

n= 18 – 30 per decade


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


Average Tonsil Position

All subjects

CM patients excluded

(n=300 per decade)

(n=22 CM pts)

Smith et al, 2013, JNS


•  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)


Tonsil Position by Decade


Tonsillar Distribution (0-10 years)


Do these findings fit with existing data?


Mikulis et al, 1992


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


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


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


-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


MRI prevalence: Meadows et al, 2000

-22,591 patients -175 were found to have tonsil position > 5 mm -0.7 % CM prevalence


Pediatric Prevalence

•  3.6 % overall •  No difference

with respect to age or sex

•  Average: 10.2 mm Strahle et al, 2011, JNS-Pediatrics


CM and Syrinx

Syrinx in 117/509 patients (23%)


CM presentation

•  68% asymptomatic at presentation


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)


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


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


CM-‐ Natural History

(Strahle et al, JNS-pediatrics, 2011)


Natural history-‐ CM and syrinx

Length Width

20 patients (13.5%): 13 with syrinx at diagnosis; 7 with new syrinx


Natural history: Surgery

6 with syrinx had surgery (2- surgery unrelated to syrinx)

Time to surgery: 2.1 years


CM natural history


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 ?


Etiology of scoliosis


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


114 with CM and Scoliosis


Natural History: 55 patients, 1 year f/u

Outcomes after PFD: 87 patients


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


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


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)


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


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


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

)



% 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



Limitations

•  Detection bias for CM •  Tonsil position may be influenced by other

factors •  Indications for imaging vary by age •  Imaging cohort not population cohort


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


Conclusions

•  Cerebellar tonsil position, like most morphometric measurements, follows a normal distribution


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


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


Conclusions

•  In most cases, it is unlikely that CM causes scoliosis when a syrinx is not present

•  Syrinx morphology differs by etiology


Acknowledgements

Brandon Smith, MD Cormac Maher, MD Hugh Garton, MD

Karin Muraszko, MD

redeﬁning(chiariimalformation:( …• female gender associated with lower tonsils (p

Documents