Jay Kantilal Satapara, Rajnikant Vasava, Nandini Bahri;
M. P. Shah Medical College,
30 years, female
30-year-old primiparous female with 7 months of amenorrhoea presented to the obstetric department for first ever antenatal checkup. Obstetric examination and routine investigations were done, all were normal. The patient was sent for ultrasonography.
On ultrasonography, no parenchymal tissue or skull vault was seen above the orbit, however, some brain tissue and occipital bone were present in the occipital region with bulging eyeballs suggestive of exencephaly. There was a defect in the occipital bone and posterior arch of the upper cervical vertebra through which brain tissue herniated, suggestive of occipital encephalocele. Liquor was increased for gestational age.
On MRI the same findings were confirmed.
The patient underwent induction of labour and the fetus was delivered.
Neural tube defects (NTDs) constitute one of the most common malformations with incidence of approximately 0.5-2/1000 pregnancies worldwide .
Dysraphism means continuity between the posterior neural ectoderm and cutaneous ectoderm. It could be either cranial dysraphism (anencephaly and encephaloceles) due to failure of closure of the anterior end of the neural tube or spinal dysraphism (spina bifida) due to failure of closure of the caudal end of the neural tube .
Exencephaly is a rare fetal anomaly in which the skull vault is absent (acrania), however, residual brain tissue is present which floats freely in amniotic fluid. It is a precursor to anencephaly and not compatible with extra-uterine life .
Encephalocele is a midline bony defect in the skull with herniation of cerebral tissue and meninges. Occipital encephalocele is the most common .
The aetiology of NTDs involves both genetic and environmental factors, however, most cases are sporadic. Increased risk of NTDs is associated with maternal folate deficiency and elevated homocysteine suggesting involvement of genes for folate and methionine metabolism. This fact is also supported by the reduction of NTDs by up to 60-70% following maternal periconceptional folate administration .
Raised alpha fetoprotein (AFP) concentrations in maternal serum is used for screening of open NTDs best detected at 16–18 weeks of pregnancy .
Ultrasound diagnosis of NTDs is usually possible in the early second trimester (10-14 wks GA) .
On ultrasound in case of exencephaly symmetrical absence of the cranial vault is noted. Rudimentary brain tissue (area cerebrovasculosa) is covered by a membrane . In encephalocele a juxtacranial mass and in most instances a bony defect can be observed after 10 weeks. If the mass is cystic, the meningocele component predominates, while a solid mass indicates predominantly encephalocele . Polyhydramnios usually develops in the second trimester due to absent or ineffective fetal swallowing .
MRI is usually not used as ultrasonography usually detects this anomaly very early, but sometimes ultrasonography does not enable an accurate diagnosis. In that case MRI is necessary as it can detect complex anomalies .
Most of NTDs are either lethal or disabling and require early termination .
Take home message:
As most of NTDs are lethal or disabling a timely detection helps in early termination of such unwanted pregnancies and ultrasonography plays a significant role in early diagnosing fetal CNS anomalies.
Written informed patient consent for publication has been obtained.
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