2 The condition, current treatments and procedure
2.1 Neural tube defects happen because the neural tube does not fuse during early embryonic development. Open neural tube defects are those in which the affected region of the neural tube is exposed on the body's surface. The most common neural tube defect is spina bifida, where the defect is in the spine. Myelomeningocele (open spina bifida) is the most severe type of spina bifida, in which the baby's spinal canal remains open along several vertebrae in the back. The spinal cord and protective membranes around it push out and form a sac, which is exposed on the baby's back. Children born with myelomeningocele may experience motor neurological deficits including muscle weakness and paralysis of the lower limbs, sensory deficit, bowel, bladder and sexual dysfunctions, and learning difficulties. The condition can be associated with Chiari II malformation (hindbrain herniation) and hydrocephalus.
2.2 Conventional treatment for myelomeningocele (open spina bifida) is immediate surgical repair of the defect within days of birth to prevent further damage to nervous tissue and reduce the risk of central nervous system infection. The immediate management may also include ventricular-peritoneal shunt placement to relieve hydrocephalus. The condition can also be treated prenatally with the aim of decreasing morbidity in the child.
2.3 Open prenatal repair for open neural tube defects is typically done before 26 weeks of pregnancy. Using general anaesthesia, a low transverse laparotomy incision is done and the gravid uterus is exposed and exteriorised. The fetus and placenta are visualised by ultrasound, and the fetus is manually positioned to allow a uterine incision (hysterotomy) over the centre of the myelomeningocele sac. The hysterotomy location is either anterior, fundal or posterior depending on the location of the placenta. The hysterotomy is made large enough to allow the neural tissue in the meningomyelocele to be dissected from surrounding tissue so that it can drop into the spinal canal. The defect is then closed. If there is insufficient dura or skin for closure, occasionally a biocellulose and dermal regeneration patch substitute may be used for repair. The uterine incision is closed and a sodium lactate solution with antibiotics is added to the uterus until the amniotic fluid index is normal. The maternal abdominal wound is then closed.
2.4 A number of variations to the procedure have been described and the technique is still evolving.