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
• Included:
 Children with
• a total of 82 children
symptomatic Chiari I
with isolated Chiari I,
 Complete set of MR
61 operated, 21
scans
asymptomatic
• Normal control group • Excluded:
 Craniosynostosis70 children (1m-15y)
related hindbrain
• Extensive range of 3D
hernia e.g. Crouzon’s
image analysis tools
 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
0.135
0.134
0.122
p=0.004
PFV/ICV
Posterior Fossa Volume
340
320
300
280
260
240
220
200
180
Group
160
Normal
140
120
HBH+Syrinx
100
HBH alone
80
0
24
12
48
36
72
60
96
84
120
108
144
132
AGE (months)
168
156
192
180
216
204
PFV / ICV Ratio
.22
.20
.18
.16
.14
Group
.12
Normal
.10
HBH+Syrinx
.08
HBH alone
0
24
12
48
36
72
60
96
84
120
108
144
132
AGE (months)
168
156
192
180
216
204
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
Method
•
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
Skull Base 3D Segmentation
Results
Normal
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
LT AC-RT AC (mm)
32
DS-FM (mm)
46
Chiari I/+ syrinx
75
63
31
27
50
40
(p=.037, p=.009)
(p=.000)
(p=.001)
(p=.101)
CG-DS-FM Angle
200
190
180
170
160
150
140
Group
130
120
Normal
110
HBH+Syrinx
100
HBH alone
0
24
12
48
36
72
60
96
84
120
108
144
132
Age (months)
168
156
192
180
216
204
IAM-FM-IAM Angle
160
140
120
Group
100
Normal
HBH+Syrinx
80
HBH alone
0
24
12
48
36
72
60
96
84
120
108
144
132
Age (months)
168
156
192
180
216
204
IAM-IAM Distance
160
140
120
100
80
Group
Normal
60
HBH+Syrinx
40
HBH alone
0
24
12
48
36
72
60
96
84
120
108
144
132
Age (months)
168
156
192
180
216
204
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