Fetal myelomeningocele repair: where are we and where can we go?

Spina bifida is one of the most prevalent major birth malformations with a worldwide incidence of approximately 1:2,000 live births. A myelomeningocele (MMC) is the most frequent form of spina bifida, characterized by the extrusion of the spinal cord and/or nerves through a bony defect of the spine into a sac filled with cerebrospinal fluid (CSF). The severity of symptoms is correlated with the level of the defect. Interruption of the spinal cord at the site of the defect can cause lifelong paralysis of the legs, bowel and bladder dysfunction, sensibility disorders of the skin, sexual dysfunction and deformation of the lower extremities and back. Most children with spina bifida are not mentally retarded, but their intelligence quotient can be reduced. Although spina bifida can be compatible with independent life, lifelong supportive care is often needed, and only about half of the patients are able to live independently as adults, even with adapted accommodations. The majority of children with spina bifida have a Chiari II malformation, which is a combination of hindbrain herniation and hydrocephalus, and is the leading cause of death in patients with spina bifida. In 45% of the fetuses with spina bifida registered within the Dutch registration of Eurocat, the parents decided to terminate pregnancy after prenatal diagnosis. This is consistent with numbers from the USA; however, in some areas of the Netherlands, these figures are considerably higher. With the introduction of the routine second trimester ultrasound scan, the number of prenatal diagnosis of spina bifida increased considerably. The classical prenatal ultrasound findings in spina bifida are typical U-shaped defect of the vertebral column in an open spina bifida, typical lemon shape of the fetal skull and banana shape of cerebellum. The ventriculomegaly occurs in the majority of cases, and club feet are also present in several cases. The current standard of postnatal care is neurosurgical closure of the defect within 48 to 72 hours after birth. However, surgical intervention does not improve neurological function, but prevents further deterioration. After birth, 80 to 90% of children with hydrocephalys will receive a ventriculo-peritoneal shunt placement to prevent additional damage to brain and brainstem. Despite the successes of postnatal neurosurgical repair and medical treatment of spina bifida, mortality still remains approximately 10%, rising to 35% in those children with symptoms of brainstem dysfunction secondary to the Chiari II malformation.