Neural tube Defects - A Case Study

Mrs X 30 years old G3 P 2+0  (no living child) with history of both pregnancies affected by neural tube defects (NTD) presented at 8 weeks and 3 days period of gestation. In the first pregnancy patient had conceived spontaneously after one year of marriage and did not seek any antenatal care. Patient delivered at a hospital and anencephaly was detected at birth. However, no comment was made on presence or absence of other anomalies. In the second pregnancy she booked at fifteen weeks pregnancy and had level 2 ultrasound at 19 weeks of gestation. She was diagnosed as occipitomeningomyelocele and opted to terminate the pregnancy. On neonatal review the diagnosis of occipitomeningomyelocele was confirmed and no other gross congenital anomalies were detected.
The parents did not consent for postmortem autopsy or chromosomal study.

Other relevant questions to ask in history: 
Present Pregnancy
• Gestational age
• History of exposure to drugs particularly which interfere with folic acid metabolism
• Any history of hyperthermia and hyperglycemia
• Intake of folic acid in periconceptional period
• History of consanguinity.

History of Previous Pregnancies
• Any history of folic acid intake in periconceptional period.
• History of hyperthermia or hyperglycemia in periconceptional period.
• History of antifolate drug intake in periconceptional period.
• Mode of diagnosis of NTDs (prenatal ultrasound, postnatal diagnosis)
• Associated malformations and dysmorphisms to delineate genetic disorders
• Fetal autopsy done or not
• Fetal karyotype done or not
• Family history of neural tube defects.

Examination
In the first half of pregnancy, there may not be anything remarkable in the examination. However, with advanced gestational age, polyhydramnios may cause increased fundal height and presence of
fluid thrill. The presentation of the fetus may be breech or face.


Q.1. How will you counsel this woman?
Ans: The woman would be counseled on the issues regarding the risk of recurrence in this pregnancy.
The risk of having a baby with neural tube defect in this pregnancy is about 10%.
Anencephaly can be detected as early as 10 weeks of pregnancy and hence she would be advised an early anomaly scan. However, for the defects in the spinal cord patient would be taken up for level II sonography between 18 to 20 weeks of pregnancy.

Q.2. If this woman comes in the preconceptional period what counseling should be done?
Ans: She is advised to take high dose of folic acid supplementation (4 mg) starting 3 months prior to
conception.
She will be counseled regarding the risk of recurrence of NTD in this pregnancy and early detection of NTDs by ultrasonography is advised.
If the woman is hyperglycemic, then she is referred to a physician for adequate control of her glycemic status before she conceives. If her glycemic status is not known then she would be evaluated with blood sugar fasting and postprandial.
If the woman is on antiepileptic therapy particularly valproate or multidrug therapy, it is advisable to switch her to monotherapy in the preconceptional period and valproate should be replaced by lesser teratogenic drugs like phenytoin. Time to change the medication is before conception as organogenesis is almost complete in the first trimester.

Q.3. What are the high risk factors which predispose to neural tube defect in fetus?
Ans: Neural tube defects are example of multifactorial inheritance. The following factors influence the development of neural tube defects:

1. Environmental agents like diabetes, obesity, hyperthermia.

2. Antifolate medications: The antifolate medications implicated in causation of NTD are valproate, carbamazepine, coumadin and aminopterin.
Neural tube defects associated with type 1 diabetes are more likely to be cervical and cervicothoracic;
with valproic exposure lumbosacral defects and with hyperthermia anencephaly.

3. Genetic Causes
• Family history
• Autosomal recessive condition—Meckel-Gruber syndrome
• MTHFR gene polymorphism such as C677T and A1298C mutations are associated with hyperhomocystinemia and folate insufficiency is thought to play a role in the phenotypic expression of MTHFR mutations.
• Recurrent NTD have been reported to be associated with partial trisomy 2p22 and 20p, resulting from a maternally derived translocation.

4. Geographical Distribution
Certain populations in particular geographic areas have increased incidence of NTDs.

Q.4. What is the significance of parental consanguinity in a case of pregnancies with recurrent neural tube defects?
Ans: There is evidence of major gene involvement in familial neural tube defects with parental consanguinity and is likely to be recessive inheritance. A single gene cause of recurrent NTD is the Meckel-Gruber syndrome. It is a rare autosomal recessive disorder and carries a 25% risk of recurrence. Other features of this syndrome triad include polycystic kidneys and polydactyly.

Q.5. What is the recurrence risk for NTDs?
Ans: Recurrence risk with one affected child is 3- 4% and after two affected children it is 10%.
The recurrence risk is 4-5% if one parent is affected.
The recurrence risk is 25% when NTD is part of Meckel-Gruber syndrome.
Recurrence risk for first degree relatives of affected children in 1 in 30 and second degree relatives is 1 in 220.

Q.6. What is the role of folic acid supplementation in prevention of neural tube defects?
Ans: There are two aspects in the administration of folic acid supplementation for prevention of NTD. Pre-conceptional intake of folic acid, beginning 3 months prior to conception in the dose of 400 microgram daily has been recommended for prevention of first occurrence of NTDs and should be continued through the first trimester of pregnancy. However, higher doses of folic acid supplementation (4 mg) are recommended for women at higher risk of NTDs. These include women with prior affected children or if the women or the partner has NTD. In women with previous affected offspring there is 70% reduction in recurrence rate. Similar doses are used in patients who are diabetic or on antifolate medication but data is limited about their benefit.

Q.7. Disruption of folic acid metabolism predisposes to which congenital abnormalities?
Ans: Several congenital abnormalities like neural tube defects, cardiac defects, cleft lip and palate,
and even Down syndrome are known to arise, at least in part from disturbance of folic acid metabolic
pathways.

Q.8. Besides NTD folic acid intake prevents which other congenital malformations?
Ans: Congenital heart diseases and cleft lip and palate are also prevented to certain extent by folic
acid intake.

Q.9. What are the sonographic features in various neural tube defects?
Ans: The antennal diagnosis of anencephaly is based on absence of fetal calvaria.
Anencephaly can be identified by ultrasound as early as 10 weeks of gestation but should be reconfirmed by a scan at around 13 weeks because ossification of the skull in some cases may not be
completed until that time.
Ultrasound diagnosis of meningomylocele is frequently based on a cystic mass protruding from the dorsal vertebral bodies without skin covering. This is ideally seen in the transverse plane as a wide
separation of the lateral processes of lamina.
Indirect sonographic signs of meningomylocele have been found to be as important as visualization
of the spinal lesion and are somewhat easier to image. These include ventriculomegaly, microcephaly,
frontal bone scalloping (lemon sign) , and obliteration of the cisterna magna with either an absent cerebellum or abnormal anterior curvature of the cerebellar hemispheres (banana sign). Banana and lemon sign are produced by caudal displacement of cerebellar vermis, fourth ventricle and medulla constituting the Arnold- Chiari II malformation. These findings are seen in over 95% of cases of neural tube defects in the middle of the second trimester. The banana sign and the lemon sign may not be present after 22 to 24 weeks’ gestation. The presence of neural tissue in the meningeal sac and level and length of the lesion should be ascertained on sonography to predict the extend and severity of the neurological deficits.
Besides the detailed evaluation of the cranium and spine, comprehensive ultrasound examination should be performed to exclude genetic syndromes

Q.10. How will you counsel and manage the couple if anencephaly is detected?
Ans: Anencephaly is lethal and can be diagnosed accurately by antenatal ultrasound.
According to the country rules termination of pregnancy may be advised. Fetal autopsy should be offered for all fetuses with anencephaly to detect other anomalies as it may form a part of genetic syndrome and helps in predicting the recurrence risk.
In recurrent NTDs fetal and parental karyotyping could be useful in the future management since
partial trisomies are the implicated cause.
However, couples who refuse termination are followed up with routine antenatal care. The woman
is more likely to have complications like polyhydramnios, malpresentation (face, breech) and postmaturity. Polyhydramnios, may result from diminished fetal swallowing, secretion of
cerebrospinal fluid directly into the amniotic cavity and excessive micturition. Postmaturity is a
consequence of absent or hypoplastic pituitary gland. During labor, shoulder dystocia and obstructed
labor should be anticipated.

Q.11. How will you counsel the patient if meningomyelocele is detected?
Ans: Patient should be counseled regarding the prognosis which depends on the presence of neural
tissue in the meningeal sac and spinal level and length of the lesion. The spinal cord below the
lesion is dysplastic and lower limb paralysis and incontinence of bowel and bladder is common.
Intelligence may be affected from either the lesion itself or the impact of treatment (shunt placement).
Early closure of the defect and ventriculoperitoneal shunting of any associated hydrocephalus should
be performed.
The option of pregnancy termination should be included in counseling if the gestational age is less than 20 weeks.
If patient plans to continue the pregnancy, a multidisciplinary team consisting of a pediatric neurologist, neurosurgeon, obstetrician, and neonatologist should manage the patient to optimize the neonatal outcome and plan surgical management.