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KEY POINTS
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Key Points

  • Open spinal cord defect that protrudes dorsally, is not covered by skin, and is associated with spinal-nerve paralysis.

  • Current prevalence in the United States is still 0.5 to 1 case per 1000 pregnancies.

  • Maternal risk factors include obesity, anticonvulsant medication, short interpregnancy interval, and genetic polymorphisms in various enzymes in the homocysteine methylation pathway.

  • Sonographic findings include a small biparietal diameter, scalloping of the frontal bones, a compressed cerebellum, lateral ventriculomegaly, Chiari II abnormalities, splaying of dorsal vertebrae, and a dorsal sac.

  • Karyotype should be performed, even in isolated neural tube defects.

  • A prospective clinical trial comparing outcomes for open fetal surgery compared to standard postnatal surgery is in progress.

  • Long-term outcome depends on the level of the spinal defect and the presence of associated anomalies.

  • Morbidity has been significantly improved by interventricular shunting for hydrocephalus and clean intermittent bladder catheterization to reduce renal complications.

  • Most neural tube defects are isolated and have a multifactorial inheritance pattern.

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CONDITION
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Myelomeningocele is an open spinal cord defect that protrudes dorsally, is not covered by skin, and is usually associated with spinal nerve paralysis. Technically, spina bifida refers to a cleft or opening in the vertebral body; this term is also used to collectively describe a group of disorders that involve the spinal cord. Lumbosacral lipomas are subcutaneous masses of fat in the lumbosacral region (Shurtleff and Lemire, 1995). Myelomeningoceles are malformations that result from failure of the neural tube to fuse during early embryogenesis, between 25 and 28 days postovulation, when the anterior and posterior neuropores close. Skin-covered defects, such as lipomyelomeningocele, result from abnormalities in secondary neurulation and retrogressive differentiation that occurs between 28 and 56 days postovulation (Shurtleff and Lemire, 1995).

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The first medical report of a myelomeningocele was made by a Dutch physician, Nicholas Tulp, who practiced between 1593 and 1674. He described a series of six cases of patients with spina bifida (Tulp, 1716).

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“Open” neural tube defects are myelomeningoceles that are not covered by skin. Leakage of α-fetoprotein (AFP) from the cerebrospinal fluid (CSF) into the amniotic fluid results in an increased transport of AFP into the maternal circulation. Screening by maternal serum AFP analysis has resulted in an increased ability to detect these lesions prenatally.

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Herniation of the spinal cord probably reduces intraspinal pressure. This allows the hindbrain to become downwardly displaced, resulting in the hindbrain herniation that is part of the Chiari type II malformation, which is seen almost exclusively in patients affected with myelodysplasia. It is characterized by caudal movement of the cerebellar vermis, brainstem, and fourth ventricle. The Chiari type II malformation is responsible for many of the early deaths in patients affected with myelodysplasia. Chiari, a professor of pathology in Prague, wrote two papers in 1891 and 1896 that described four types of pathologic changes occurring in 40 affected ...

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