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KEY POINTS
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Key Points

  • Encephalocele is a rare defect of the cranial vault, which may contain meninges only, or also neural tissue.

  • Most cases in Caucasian populations are occipital in location, while Southeast Asian populations are more commonly frontal.

  • Causes include maternal diabetes, rubella, hypervitaminosis-A, isolated neural tube defect, amniotic-band syndrome, aneuploidy such as trisomies 13 and 18, and genetic syndromes such as Meckel–Gruber.

  • Differential diagnosis includes cystic hygroma, cervical teratoma or hemangioma, or epidermal scalp cysts, while false-positive diagnoses have been made by mistaking clumps of fetal hair in the third trimester.

  • Natural history and prognosis depends on the presence of associated malformations and presence of neural tissue within the meningeal sac.

  • Pregnancy management includes prenatal MRI to confirm absence of neural tissue within the sac, and possible elective cesarean delivery if prognosis appears favorable.

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CONDITION
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Encephalocele refers to the herniation of cranial contents through a defect in the skull. This term includes both encephaloceles, which contain meninges and brain, as well as meningoceles, which consist of meninges and cerebrospinal fluid. Empty meningoceles are not as common as encephaloceles. Encephaloceles are subdivided according to their location: occipital and frontal. This distinction is important, as each of the conditions has a different prognosis based on their location. In occipital encephaloceles, the defect lies between the lambda and foramen magnum (Simpson et al., 1984). These encephaloceles are considered part of the spectrum of neural tube defects. Sincipital or frontal encephaloceles are situated between the bregma and anterior margin of the ethmoid bone. The majority of these encephaloceles extend into the root of the nose, and they are not considered a form of neural tube defect, but rather are likely secondary to an environmental exposure. Occipital encephaloceles are considerably more common than frontal encephaloceles in populations of European descent, whereas frontal encephaloceles are much more common in populations from Southeast Asia.

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The cause of encephalocele is unknown, but occipital encephaloceles are thought to be caused by failure of closure of the rostral neural pore. The majority of encephaloceles occur in the midline; however, they may also result from disruption of fetal-skull formation, such as in the amnion rupture sequence (Chervenak et al., 1984). Encephaloceles occur between 25 and 50 days of gestation for anterior defects and up to 60 days for posterior defects (Brown and Sheridan-Pereira, 1992).

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INCIDENCE
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In a recent review from New Zealand, encephaloceles were seen in one in 13,000 births (Monteith et al., 2005). In an earlier U.S. study extending more than 17 years, Wiswell et al. (1990) documented 112 cases of encephalocele in 763,364 livebirths, or 0.15 per 1000 livebirths. Of these infants with encephaloceles, 40% had associated congenital anomalies. Encephalocele is more often associated with extra-CNS malformations than anencephaly or spina bifida (Kalien et al., 1998). In an Australian study, the incidence of ...

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