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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

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.

A B C

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

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.

 

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Bruner, 1999 Ritter,  1999 occipital encephalocele atresic encephalocele Click on figure for enlargement. Figure must be centered. types of spina bifida place pointer on structures (not all are labeled) orbit orbit cerebral mass frontal lobe nasal cavity cerebral mass enlarged temporal horn of the lateral ventricle enlarged temporal horn of lateral ventricle