Aqueductal
Stenosis
The aqueduct
of Sylvius is a narrow structure that allows communication between the
third and fourth ventricles. The cerebrospinal fluid produced in the choroid
plexus of the lateral ventricles and the roof of the third ventricle travels
through the aqueduct of Sylvius to reach the fourth ventricle on its way
to the subarachnoid space. Congenital aqueduct of Sylvius stenosis or
atresia may be sporadic or of X-linked inheritance. X-linked inheritance
(Bickers-Adams syndrome) accounts for 2% of patients with aqueductal stenosis.
Boys with Bickers-Adams syndrome often have flexus adductus thumb deformity
(Figure 293.1).
Figure 293.1.— Bickers-Adams syndrome. [A] Macrocephaly due
to aqueduct of Sylvius stenosis with bilateral cortical thumbs; [B] flexus
adductus thumb deformity.
The head of patients with congenital
aqueduct of Sylvius stenosis or atresia is large from birth (Figure 293.2
[A]). Cesarean section is often required because of cephalopelvic disproportion.
There is usually frontal bossing, dilated scalp veins, and splitting of
the sutures. Transillumination is positive in severe cases (Figure 293.2
[B]). The eyes may deviate downward. The diagnosis is established by MRI
of the brain.
Figure 293.2.— [A] Macrocephaly due to aqueduct of Sylvius
stenosis; [B] transillumination of the same patient.
Aqueduct
of Sylvius stenosis may also occur with meningitis. The diagnosis is established
by MRI of the brain (Figure 293.3).
Figure 293.3.—
Aqueduct of Sylvius stenosis. [A] T1-weighted images
demonstrating hydrocephalus due to aqueductal stenosis. [B] Cerebrospinal
fluid flow study demonstrating no flow through the aqueduct.
Dandy-Walker
Malformation
Patients
with Dandy-Walker malformation may present with macrocephaly during the
neonatal period. Macrocephaly during the neonatal period usually results
from an enlarged posterior fossa (Figure 293.4).
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B
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Figure 293.4.—
[A] Large posterior fossa with ventral compression of the brainstem; [B]
absence of the cerebellar vermis.
The
large posterior fossa results in a dolichocephalic appearance which should
be differentiated from dolichocephaly and bathrocephaly. Dolichocephaly
(keel-shaped head) is due to sagittal suture synostosis. In neonates with
premature closure of the sagittal suture most of the dolichocephalic appearance
of the head is due to frontal prominence. Bathrocephaly (step in the head)
is a normal finding in the neonatal skull that disappears after a few
months. Bathrocephaly is characterized by bulging of the interparietal
part of the occipital bone (Figure 293.5).
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B
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Figure 293.5.—
Bathrocephaly. [A] Lateral skull film demonstrating step-like elongation
of the posterior aspect of the skull. [B] The occipital bone protrudes
more posterior than the parietal bone.
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