Posterior Fossa Volume and Skull Base Geometry in Children

with Chiari I Malformation

S.Sgouros

Birmingham Children’s Hospital

Birmingham, U.K.

Acknowledgements

• Kal Natarajan, Computer Scientist at the Neuroscience Informatics Laboratory

• Menia Kountouri, Research Fellow

• The Neuroscience Informatics Laboratory at ICH/BCH is supported by the Bernard Williams Syringomyelia Research Fund

Hindbrain Hernia – Chiari I

• Hindbrain hernia is considered to be due to maldevelopment of the posterior cranial fossa leading to small volume

• Geometrical studies of 2D sagittal projections and quasi 3D studies

• Lack of systematic analysis in paediatric age group

3D Morphometric Analysis of Chiari I

• 1998-2007 • a total of 82 children

with isolated Chiari I, 61 operated, 21 asymptomatic

• Normal control group 70 children (1m-15y)

• Extensive range of 3D image analysis tools

• Included: Children with

symptomatic Chiari I Complete set of MR

scans

• Excluded: Craniosynostosis-

related hindbrain hernia e.g. Crouzon’s

Shunt prior to craniovertebral decompression

Posterior Fossa Volume

Aim of the Study

• To establish whether the volume of the posterior fossa in children with Chiari I is smaller than normal controls, as has been previously postulated

• To establish the correlation between posterior fossa volume and the development of syringomyelia

Patients

• 42 children (24 Male, 57%)

• Mean age: 127 m (range: 36-204 m)

• Syrinx present pre-op: 25 patients (59%)

• Comparison with 51 normal children of similar age

Method

• Segmentation technique on pre-op MRI scans

• Parameters measured: Posterior Fossa Volume Intracranial Volume Posterior Fossa to Intracranial Volume ratio

• Factor analysed: syringomyelia preop

• One way ANOVA, graphic data analysis (LOWESS smoothing technique)

Segmentation

Results

Normal CMI no syrinx CMI+syrinx (n=51) (n=17) (n=25)

ICV (cm3) 1383 1459 1400 p=0.363

PFV (cm3) 186 196 171 p=0.036

PFV/ICV 0.135 0.134 0.122 p=0.004

Posterior Fossa Volume

AGE (months)

216

204

192

180

168

156

144

132

120

108

96

84

72

60

48

36

24

12

0

Po

ste

rio

r F

oss

a V

olu

me

(cm

3)

340

320

300

280

260

240

220

200

180

160

140

120

100

80

Group

Normal

HBH+Syrinx

HBH alone

PFV / ICV Ratio

AGE (months)

216

204

192

180

168

156

144

132

120

108

96

84

72

60

48

36

24

12

0

PF

V/I

CV

Ra

tio.22

.20

.18

.16

.14

.12

.10

.08

Group

Normal

HBH+Syrinx

HBH alone

PFV in Chiari I

• Two different varieties of Chiari I

• Children with Chiari I without syringomyelia have normal posterior fossa volume

• Children with Chiari I and syringomyelia have a smaller posterior fossa volume than normal

Skull Base Geometry

Aim of the Study

• To establish whether the skull base in children with Chiari I is underdeveloped compared to normal controls, as it has been previously postulated

• To establish the correlation between skull base geometry and the presence of syringomyelia

Patients

• 30 children (17 Male, 57%)

• Mean Age: 128 m (range: 36-204 m)

• Syrinx present pre-op: 16 patients (53%)

• Comparison with 42 normal children of similar age

• Segmentation technique on pre-op T2w axial MRI scans:

Angles Crista Galli - Dorsum Sellae -

Foramen Magnum LT IAM - Foramen Magnum - RT

IAM LT AC-CG-RT AC LT IAM - Dorsum Sellae - RT IAM

Distances LT - RT IAM LT AC – RT AC Dorsum Sellae - Foramen Magnum

• Effect of syringomyelia• One way ANOVA analysis• Graphic data analysis

Method

Skull Base 3D Segmentation

Results

Normal Chiari I/- syrinx Chiari I/+ syrinx

CG-DS-FM 135° 145° 151° (p=.000)

LT IAM-FM-RT IAM 110° 122° 123° (p=.001)

LT AC-CG-RT AC 34° 29° 29° (p=.000)

LT IAM-DS-RT IAM 96° 97° 101° (p=.394)

LT IAM-RT IAM (mm) 58 75 63 (p=.000) LT AC-RT AC (mm) 32 31 27 (p=.001)DS-FM (mm) 46 50 40 (p=.101)

(p=.037, p=.009)

CG-DS-FM Angle

Age (months)

216

204

192

180

168

156

144

132

120

108

96

84

72

60

48

36

24

12

0

CG

-DS

-FM

Ang

le200

190

180

170

160

150

140

130

120

110

100

Group

Normal

HBH+Syrinx

HBH alone

IAM-FM-IAM Angle

Age (months)

216

204

192

180

168

156

144

132

120

108

96

84

72

60

48

36

24

12

0

IAM

-FM

-IA

M A

ngle

160

140

120

100

80

Group

Normal

HBH+Syrinx

HBH alone

IAM-IAM Distance

Age (months)

216

204

192

180

168

156

144

132

120

108

96

84

72

60

48

36

24

12

0

IAM

-IA

M D

ista

nce

160

140

120

100

80

60

40

Group

Normal

HBH+Syrinx

HBH alone

Skull Base Geometry in Chiari I

• Chiari I overall have (in comparison to normal) : longer anterior fossa wider and steeper posterior fossa and different slope / angle of clivus

• Patients with syringomyelia have slightly different skull base geometry than those without

Conclusions

• Chiari I + Syringomyelia: small posterior fossa volume

• Chiari I – Syringomyelia: normal posterior fossa volume

• Chiari I: all skull base structurally different from normal

• Differences in skull base geometry in syringomyelia

• Unlikely that the development of syringomyelia is an evolution in the natural history of Chiari malformation (difficult for posterior fossa to become smaller and geometry to change, as the syringomyelia develops, unless there is a primary skull base synostosis)

Possible Pathogenesis

• Possible different pathogenesis for the two subgroups of the Chiari I Chiari I – syrinx: single hit (mesodermal deformity) Chiari I + syrinx: double hit (mesodermal deformity +

cavitation)

• Ab initio formation of syringomyelia “loss” of CSF in the spine smaller posterior fossa (analogous to open myelomeningocele)

• Anterior fossa deformity secondary to posterior fossa mesodermal defect or primary malformation affecting all the skull base?

Syringomyelia 2007

• Major international conference on syringomyelia

• Rugby, U.K.

• October 23-26, 2007

• Abstract Closing Date: 30th June 2007

• www.syringomyelia2007.org