eMedicine Specialties > Radiology > Pediatrics

Spinal Dysraphism/Myelomeningocele: Follow-up

Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad National Guard Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia
Coauthor(s): Ian Turnbull, MB, ChB, MD, DMRD, FRCR, Lecturer, Department of Radiology, University of Manchester; Consulting Neuroradiologist, Hope Hospital, Salford, Manchester and North Manchester General Hospital, UK; Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute; Durre Sabih, MBBS, MSc, Visiting Faculty, Department of Nuclear Medicine, Pakistan Institute Applied Sciences and Nishtar Medical College; Director, Multan Institute of Nuclear Medicine and Radiotherapy; Riyadh Al-Okaili, MBBS, Interventional/Therapeutic and Diagnostic Neuro-Radiologist, King Abdulaziz Medical City
Contributor Information and Disclosures

Updated: Jan 14, 2009

Intervention

Studies in the 1980s and 1990s showed that folic acid deficiency was an important cause of myelomeningocele and that 50% of cases of neural tube defects (NTDs) are preventable. Therefore, in 1992, the US Public Health Service (USPHS) recommended that all women who anticipated becoming pregnant should take folic acid at a dosage of 0.4 mg/d. In 1996, the USPHS made the fortification of cereal grain with folic acid mandatory.

Intrauterine repair of the myelomeningocele is now possible; early studies suggest that such repair may decrease the incidence of the development of significant hydrocephalus without affecting motor outcome, despite decreased exposure injury to the dysplastic cord.

Surgery for NTDs is performed as a matter of urgency immediately after birth if CSF leakage is present; in the absence of CSF leakage, surgery is generally performed within the first 24-48 hours.

Occasionally, hydrocephalus associated with a myelomeningocele arrests spontaneously. However, in most cases, shunt surgery is required. Shunt techniques include ventriculoperitoneal, ventriculoatrial, and ventriculopleural procedures. Ventriculoperitoneal shunting is the preferred modality.

Orthopedic surgery may be required for a variety of musculoskeletal complications associated with myelomeningocele. Progressive spinal kyphosis or scoliosis are common and may result in a variety of neurologic and cardiopulmonary compromises. Spinal stabilization may be necessary to correct kyphosis. Paralytic scoliosis develops in approximately one half of children as a result of asymmetric muscle forces, pelvic obliquity, unilateral hip dislocation, or a progressive neurologic process such as syringohydromyelia. Some of these orthopedic complications may initially be managed conservatively; eventually, they may require corrective surgery, such as surgical fusion.

Lower-limb deformities, such as knee flexion, may be managed by means of simple tenotomy of the knee flexor tendons. Extension contractures are managed with extensor tendon release when not amenable to orthotic measures.

Internal and external tibial torsion are commonly associated with myelomeningoceles. If no improvement occurs with growth or conservative measures by the age of 6 years, derotation osteotomy with plate fixation is the preferred surgical technique.

A clubfoot associated with myelomeningocele usually requires surgical correction in the first year of life; it generally requires multiple release procedures with tendon excisions. Muscle tendon transfer may be required in older children to correct anomalies such as calcaneovarus and calcaneovalgus.

To manage urinary bladder drainage problems, clean intermittent catheterization is preferred to long-term indwelling catheters. Catheterization may be used from birth to reduce bladder pressures and to establish social continence at a developmentally appropriate time.

Urologic surgical procedures, such as a temporary vesicostomy, augmentation cystoplasty, and urinary diversion, are surgical techniques available to manage urinary bladder drainage problems.

Intravesical transurethral bladder stimulation has been shown to improve functional bladder capacity, sensation, and compliance. However, the technique has not met with success in achieving voluntary bladder control.

Fetal therapy is a rapidly advancing specialty and an integral part of interventional sonography. Open hysterotomy has been performed for the repair of myelomeningocele, resection of sacrococcygeal teratoma in fetuses with nonimmune hydrops, and treatment of an enlarging congenital cystic adenomatoid malformation that was not amenable to thoracoamniotic shunting.²⁰

To date, more than 100 women and their fetuses have undergone in utero surgery for repair of spinal defects. No fetus has been cured, and published reports indicate no significant improvement in the level of paralysis, as compared with optimal postnatal care. However, approximately one third of the fetuses may show improvement in Chiari malformation, decreasing the need for shunt surgery.²¹

Serious complications, including uterine rupture, maternal bleeding, fetal death, and prematurity, have been reported with fetal surgery. Moreover, the long-term effects of fetal surgery are not known. A multicentric, randomized, controlled trial of fetal surgery for myelomeningocele sponsored by the National Institutes of Health is underway; its results are keenly awaited.

Medicolegal Pitfalls

• Couples should be fully counseled before any screening is done.
  • Antenatal screening begins with a measurement of serum alpha-fetoprotein (AFP) levels at 16-18 weeks' gestation. Levels of AFP are highest in early pregnancy. An increase in the serum AFP level at 16 weeks may indicate the presence of a neural tube defect (NTD).
  • Normally, AFP is not present in the amniotic fluid, but in cases of ONTD, it appears in the amniotic fluid through a direct communication between the CSF and the amniotic fluid. AFP becomes detectable between the fifth and ninth weeks of gestation. It also crosses the placenta and reaches maximal maternal blood levels around the 14th week.
  • Values 2.5 times the normal value are considered indicative of NTD.
  • In about 75% of open spina bifida cases, results of maternal AFP testing are positive.
  • NTDs may be identified with the use of amniocentesis at 16-18 weeks' gestation in conjunction with detailed ultrasonographic scanning after the 16th week. Unfortunately, diagnostic screening for spina bifida is not 100% accurate. Levels higher than normal may indicate spina bifida. However, high levels may also be related to inaccurate dates, multiple pregnancies, and false-positive findings (about 1 in 7 findings).
  • Amniocentesis poses a small risk of fetal death, preterm labor, and hemorrhage.
• Overlying intact skin may mask the underlying abnormality of the lower spine, and the cutaneous signs of spinal dysraphism may be subtle.
  • Early recognition of these findings is important because symptoms may not be obvious until later in childhood or early adult life, when irreversible neurologic deficits may already have occurred. If the dysraphism and associated cord tethering are neglected, irreversible urologic and neurologic damage may occur.
  • Because the disease is progressive, prophylactic surgery is indicated in most cases.

Special Concerns

• Neural tube defects (NTDs) exact an enormous emotional and economic toll on families and health care systems in both developed and developing countries. The tragedy is that NTDs are preventable simply by having women take a folic acid supplement during the 2 months before they become pregnant. For all women, supplementation with folic acid, 0.4 mg daily before conception and for the first 3 months of pregnancy, reduces the risk of having a baby with spina bifida. Women considered to be at risk should take a higher dose (4 mg) of folic acid.
• The etiology of spina bifida or anencephaly is multifactorial and includes genetic factors, environmental influences, and folic acid deficiency in the mothers. It is known that if a woman has had 1 baby with an NTD, the chance of having another affected baby is about 1 in 20. About one half of this risk is of anencephaly, and the other half is of spina bifida. A woman is at equal risk for either spina bifida or anencephaly in future pregnancies, regardless of which of these NTDs occurred in a previous pregnancy. She is also at risk for having a baby with an NTD if she has a close relative who has had a baby with either spina bifida or anencephaly or is taking certain drugs to control epilepsy. Ultrasonography is performed in high-risk pregnancies. If the sonograms do not clearly show an NTD, amniocentesis with alpha-fetoprotein (AFP) measurements is indicated.
• In 1978, Kleijer and associates measured amniotic fluid levels in 2180 patients judged to be at risk for fetal abnormality on the basis of previous history, family history, advanced maternal age, suspected fetal growth retardation, or the presence of hydramnios. In 12 patients examined before 20 weeks' gestation, pregnancy was terminated because of an increase in amniotic fluid AFP level. Eleven fetuses had NTDs. No false-negative results were observed in the 1927 patients who were tested before 20 weeks' gestation for whom the outcome of pregnancy was known. In patients tested after 20 weeks' gestation, the amniotic fluid AFP concentration was increased in 20 fetuses with anencephaly, in 9 fetuses with severe congenital malformations without NTDs, and in 1 apparently healthy fetus. Of 428 patients with a previous offspring who had an NTD, only 8 (1.9%) had a fetus with an NTD.
• Allen and associates performed amniotic fluid AFP assays and targeted sonography in 376 antenatal patients at risk for an NTD (high-risk group).²² In addition, 2436 patients underwent amniocentesis, sonographic screening, and amniotic-fluid AFP assays for other indications (low-risk group). They found 10 NTDs in the high-risk group (7 open, 3 closed) and 3 in the low-risk group (all open). Two of the 3 closed defects were detected prenatally. The predictive value of an elevated AFP level for an abnormal fetus was higher in the high-risk group (6 of 6, 100%) than in the low-risk group (1 of 6, 17%). When both sonographic and AFP results were normal, the likelihood of a normal outcome was high in both groups (99.7% and 100%). In the low-risk group, the likelihood of an abnormal outcome in women with elevated AFP level and a normal sonogram was low (0 of 5).
• Holschneider and associates described their experience with antenatal diagnosis for pediatric surgery.²³ They published a report concerning an increase in sonographic examinations at the First University Gynecological Hospital of Munich from 6000 studies in 1969 to more than 13,000 studies in 1982. They analyzed the increased rate of antenatally diagnosed malformation and the accuracy of antenatal sonographic diagnosis.
  • In their study, a correct diagnosis was made in over 80% of cases. However, the diagnosis was incomplete in approximately 40% because of associated malformations of the GI tract, congenital heart disease, myelomeningocele in a correctly diagnosed hydrocephalus, and unrecognized cases.
  • False-positive results were found in 17.5% of cases; false-negative results occurred in 12.7%. They concluded that, because of the uncertainty of antenatal diagnosis and the uncertainty of many physiologic parameters, intrauterine surgical treatment could not be advocated at present.
  • Intrauterine measures were confined to cases involving punctures, the administration of drugs, and diagnostic procedures. The authors discussed the effect of further consequences, such as termination of pregnancy, psychological aspects, and possible development of intrauterine therapy. Their report reflected results obtained with old sonographic technology. Since the time of their study, sonographic technology has improved. Nevertheless, fetal surgery is still in its infancy.
• Measurement of amniotic fluid AChE levels confirms the diagnosis. Termination of the pregnancy is advised if results of this test are positive.
• The sensitivity of the entire screening process is estimated to be 86% for anencephaly and 78% for open spina bifida. The specificity is 99.99%.
• Special racial groups should be targeted in terms of prophylaxis and screening; such groups include people of Celtic origin (Irish), the European white population, and the North American Hispanic population (which has a risk more than 3-fold higher than that of non-Hispanic whites). Migration studies in the white migrant population showed a prevalence of NTDs that more closely corresponded to the risk of the place to which they had migrated, as opposed to the place of their origin. By contrast, descendants of the black and Asian migrant populations in Europe and North America have prevalences not substantially higher than those of their parent countries. These variations are consistent with the theory that NTDs are a phenotypically heterogeneous group of malformations with multifactorial inheritance in some cases and single gene defects in others.
• The value of AChE qualitative analysis as a tool for the diagnosis of fetal NTD was investigated in a series of 2815 amniotic fluid samples. This test enabled successful identification of all 84 cases of ONTDs, 16 of which had been missed with ultrasonography. AChE electrophoresis made it possible to exclude 1 false-positive sonographic diagnosis of NTD and to differentiate meningocele from myelomeningocele. The authors' experience suggests that AChE electrophoresis should be performed in all cases, in place of amniotic fluid AFP estimations; in all cases of fetal abnormality detected with sonography, especially in fetal hydrocephaly; and for all pregnant women who have had a previous pregnancy with an NTD.

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