ENCEPHALOCELE
Encephaloceles are due to
failure of the anterior neuropore to close. In the general population,
about 75% of the encephalocele are located in the occipital region (Figure
258.1). The diagnosis of an occipital encephalocele is usually obvious
(Figure 258.1), but occasionally it requires a high index of suspicion
(Figure 258.2).
A |
B |
 |
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Figure 258.1.— [A] Large occipital encephalocele.
[B]
CT of the brain showing brain tissue protruding through an occipital
bone opening.
Subtle occipital
encephalocele (Figure 258.2) may increase in size during the neonatal
period. In high occipital encephalocele, other central nervous system
abnormalities are usually not present. In low occipital encephalocele,
there may be associated cerebellar and brainstem abnormalities.
Meckel-Gruber syndrome is
characterized by posterior encephalocele, microcephaly with sloping
forehead, cerebral and cerebellar hypoplasia, polydactyly, polycystic
kidney, and cryptorchidism. Meckel-Gruber syndrome has an autosomal
recessive inheritance.
Anterior
encephaloceles (Figure 258.3) are more common than posterior encephaloceles
among neonates of oriental ancestry. The possibility of an anterior
nasal encephalocele should be considered in any neonate with an apparent
coanal atresia. Parietal encephaloceles are rare.
Figure 258.3.—
MRI appearance of an anterior encephalocele. A. Cerebral mass between
the orbits. B. Sagittal view demonstrating absence of the floor of the
nose and drop of frontal lobe into the nasal cavity. C. Dilated tips
of the temporal horns and cerebral mass between the orbits and protruding
into the right orbit.
Magnetic resonance imaging
or CT are the studies of choice in neonates with encephalocele (Figures
258.1,2,3). The point of origin of the occipital encephalocele is determined
by observation. The point of origin of anterior encephalocele may be
difficult to determine, especially if it is in
the nasal or oral region. Determining the origin of the encepalocele
in these patients may require special MRI or CT views. In addition to
the origin of the encephalocele, MRI and CT of the brain usually demonstrate
the presence of associated brain and brainstem anomalies. The treatment
of encephalocele is surgical.
A |
B |
 |
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Figure 258.3.— [A] Posterior parietal encephalocele; [B]
CT
of the brain demonstrating the encephalocele and hydrocephalus.
MENINGOMYELOCELE
Meningomyeloceles
are a type of spina bifida.
Meningomyeloceles usually occur in the lumbosacral region (Figure 258.4).
Lumbar myelomeningoceles are due to failure of the posterior neuropore
to close. Myelomeningoceles that involve the lumbar region are more
likely to be associated with hydrocephalus than myelomeningoceles at
any other level of the spinal cord. Signs of hydrocephalus are full
anterior fontanelle, wide sagittal sutures, and a large head. Signs
of hydrocephalus usually occur by 6 weeks of age. Treatment of myeolomeningocele
is surgery as soon as possible. If the myeolomeningocele is not covered
by skin, the sack should be kept moist and sterile prior to surgery.
Endoscopic coverage of fetal myelomeningocele in utero may prevent damage
to the spinal cord by avoiding the exposure of the spinal cord to the
urea-rich amniotic fluid produced late in pregnancy.
Echocardiograms are warranted in neonates with myelomeningocele because
cardiac malformation occurs in 39% of these patients.
Figure 258.4.— Lumbar myelomenigocele with a partially skin-covered
sac.