Fetal Surgery for Myelomeningocele and the Incidence of Shunt-Dependent Hydrocephalus

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Abstract
Myelomeningocele is the most common congenital anomaly of the central nervous system and a major cause of serious developmental disability. The birth prevalence reported in the United States from 1983 to 1990 was 4.4 to 4.6 cases per 10,000 live births.1 Myelomeningocele results from the failure of caudal neurulation during the fourth week of gestation. The lesion is characterized by protrusion of the meninges through a midline bony defect of the spine, forming a sac containing cerebrospinal fluid and dysplastic neural tissue. Most infants with myelomeningocele develop paraparesis and urinary incontinence. The Chiari II malformation, including herniation of the cerebellum and hindbrain, is almost universally present and is usually associated with hydrocephalus. The severity of hydrocephalus usually worsens after neurosurgical repair of the lesion in the newborn, requiring placement of a ventricular shunt apparatus. Despite the necessity of a shunt, many children with myelomeningocele will manifest developmental delay and learning disabilities. Structural abnormalities due to muscular imbalance, including talipes and dislocation of the hips, are common.