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In Depth Tutorials and Information
CHAPTER
36
Osteogenesis Imperfecta and Basilar
Invagination
Kyriakos Papadimitriou, Ali A. Baaj and Jean-Paul Wolinsky
The Johns Hopkins Hospital, Baltimore, MD, USA
INTRODUCTION
of the posterior skull base.
7
This in turn permits upward
translocation of the rostral cervical spine into the poste-
rior fossa.
Eight to 25% of patients with OI eventually develop
BI, but not all patients who develop BI become clinically
symptomatic.
8
According to Imagama et al. the rate of
OI in association with BI ranges from 25 to 71%.
9
Basilar
invagination has been reported in all clinical subtypes of
OI except the lethal perinatal (type II) variant.
6
However,
its incidence is reported more frequently with type III
OI as it was observed in 15% of 33 patients.
10
Similarly,
Harkey et al. reported basilar impression in two patients
with the more severe type III variant of OI, comprising
half of their series patients.
11
McAllion and Patterson
reviewed the causes of death in patients with OI exclud-
ing infants and the perinatal form (type II).
12
The authors
reported that OI type III increases the risk for death sig-
nificantly due to respiratory arrest and basilar invagi-
nation. Patients with OI type I and type IV often had a
normal lifespan and died of unrelated illnesses.
2
OI and BI have also been reported to be associated
with hydrocephalus; however, many of these cases are
asymptomatic.
13
The exact mechanism remains unclear.
Some authors suggested that BI is caused by impaired
outflow from the foramen of Monro resulting in hydro-
cephalus and a mismatch between head weight and the
relatively small surface area of the craniocervical junc-
tion.
14
Weakness of the bone or repetitive microfractures
in the region of the foramen magnum can potentially
lead to hydrocephalus.
14
Cheung et al. observed that
the height z-score is the strongest predictor of skull base
abnormalities.
15
Likewise, the etiology of BI in OI remains
unclear. Some evidence supports a similar hypothesis that
BI in OI develops as a result of variation in skull shape,
Primary basilar invagination (BI) is thought to be
a developmental defect of the chondrocranium and
is often associated with notochord malformations.
1
Secondary basilar impression results from skeletal dis-
eases and resultant bone softening, as is frequently seen
in osteogenesis imperfecta (OI), Paget disease, Hurler
syndrome, hyperparathyroidism, osteomalacia, Hajdu-
Cheney syndrome and achondroplasia.
1
Compression
fractures of the vertebral bodies, kyphoscoliosis and lum-
bar spondylosis are common involvements of the axial
skeleton.
2
OI was first reported to be linked to basilar
impression in 1942.
3,4
Basilar impression (relative lowering of the cranial
base with consequent positioning of the uppermost ver-
tebral structures above the caudal border of the skull) is
a rare mechanical deformity of the craniocervical junc-
tion that is characterized by either basilar invagination or
cranial settling. Basilar invagination (e.g., from OI) is due
to the infolding of the basiocciput and is an O-C1 disease
(
Figure 36.1
). Cranial settling (e.g., from rheumatoid dis-
ease) is the rostral displacement of the high cervical spine
and is due to C1-C2 disease (
Figure 36.2
). Basilar impres-
sion comprises both basilar invagination and cranial
settling.
Ackermann described basilar impression in 1790 and
the anatomists Berg and Retzius first coined the term
“basilar impression” in 1855.
3
Frank et al. suggested that
the weight of the cranium and its contents exceeds the
load bearing capacity of the “soft” bones at the skull base,
deforming them over time.
5,6
It is probable, as Pozo et al.
reported, that recurrent microfractures in the region of
the foramen magnum underlie the progressive infolding
