Ireland) were many times implicated in an increased rate of both myeloschisis and anencephaly, but the effects of starvation and vitamin deficiency could never be separated from the potential effect of a toxic factor. It has now been established by numerous case-control and randomized treatment trials that inadequate intake of folate in early pregnancy is associated with an increased risk of these malformations. Folic acid, given before the 28th day of pregnancy is protective; vitamin A may also have slight protective benefit. Similar associations have been found with less certainty with exposure during pregnancy to certain antiepileptic drugs, particularly valproic acid and carbamazepine. Maternal diabetes and possibly obesity have been risk factors in some epidemiologic studies, as summarized by Mitchell and colleagues. The greatest risk, however, almost 30-fold higher, attaches to a previous pregnancy affected with spina bifida in particular.
Diagnosis As with anencephaly, the diagnosis can often be inferred from the presence of alpha-fetoprotein in the amniotic fluid (sampled at 15 to 16 weeks of pregnancy) and the deformity confirmed by ultrasonography in utero. Blood contamination is a source of error in the fetoprotein test (Milunsky). Acetylcholinesterase immunoassay, done on amniotic fluid, is another reliable means of confirming the presence of neural tube defects.
In the case of meningomyelocele, the child is born with a large externalized lumbosacral sac covered by delicate, weeping skin. The defect may have ruptured in utero or during birth, but more often the covering is intact. There is severe dysfunction of the cauda equina roots or conus medullaris contained in the sac. Stroking of the sac may elicit involuntary movements of the legs. As a rule, the legs are motionless, urine dribbles, keeping the patient constantly wet, there is no response to pinprick over the lumbosacral dermatomal zones, and the tendon reflexes are absent. In contrast, craniocervical structures are normal unless a Chiari malformation is associated, as it often is (see further on). Differences are noted in the neurologic picture depending on the level of the lesion. If the lesion is entirely sacral, bladder and bowel sphincters are affected but legs escape; if lower lumbar and sacral, the buttocks, legs, and feet are more impaired than hip flexors and quadriceps; if upper lumbar, the feet and legs are sometimes spared and ankle reflexes retained, and there may be Babinski signs. The two common complications of these severe spinal defects are meningitis and progressive hydrocephalus from a Chiari malformation (see below). The subject of spina bifida and neural tube defects was reviewed by Botto and colleagues and by Mitchell and coworkers.
Treatment Prevention by the administration of folate during pregnancy is obviously paramount. Opinions as to proper management of the established lesion vary considerably. Excision and closure of the coverings of the meningomyelocele in the first few days of life are advised if the objective is to prevent fatal meningitis. After a few weeks or months, as hydrocephalus reveals its presence by a rapid increase in head size and enlargement of the ventricles, a ventriculoperitoneal shunt is required. Less than 30 percent of such patients survive beyond 1 year and the long-term results of treating these patients have not been encouraging. In a series of 270 children, Lorber reported that 80 to 90 percent of their surviving patients are developmentally delayed to some degree and are paraplegic. The decision to undertake rather formidable surgical procedures is being questioned more frequently. Exceptionally, patients with meningomyelocele, and most of those with lumbar meningocele, are cognitively normal.