**5. Diagnosis**

*Congenital Anomalies in Newborn Infants - Clinical and Etiopathological Perspectives*

In addition to the potential environmental risk factors as outlined above, congenital CNSA may be a consequence of genetic disorders. NTD, including encephalocele, spina bifida, and exencephaly, have become less prevalent since the widespread consumption of folic acid by pregnant women. So the etiology has shifted toward mutations in folate-responsive or folate-dependent pathways [27]. Knowing the underlying genetic disorders for congenital CNS anomalies helps in counseling about the existing pregnancy, as well as the risk of recurrence in future ones. Sophisticated genetic investigations are available to detect chromosomal

While a low rate of karyotype abnormality has been reported in isolated ventriculomegaly (0 to 3.8%) [28], Dandy-Walker malformation has been associated with 50% of aneuploidies if associated with other anomalies [29]. In a nearly similar pattern, isolated holoprosencephaly is not accompanied by any significant genetic anomaly; however, 25 to 50% of cases have been reported to have aneuploidies if associated with other organ anomalies. Holoprosencephaly is detected in 70% of Trisomy 13 cases. In the cases with NTDs, Trisomy 13 and 18 are the most commonly reported aneuploidies [30]. Studies have reported notable connections between deletions on the long arm of the 13th chromosome and CNS

Genes participating in folate metabolism have been studied for the pathogenesis of NTDs. The C677T and A1298C polymorphisms of methylenetetrahydrofolate reductase (MTHFR), encode a key enzyme of folate metabolism responsible for homocysteine remethylation [16]. These polymorphisms are associated with a 1.8fold increase in the risk of NTDs. More than 200 genetic models of NTD have been described in mice that can affect the open NTD phenotypes, such as anencephaly, open spina bifida and craniorachischisis. Their roles in human NTDs are understudy. Some inbred strain variation in the penetrance and expressivity of NTD phenotypes in mice have suggested the roles of modifier gene function. The Cecr2 mutation that causes exencephaly in mice is strongly affected in its expression by one or more modifier genes on Chromosome 19. Strain differences have also been described for non-genetic causes of NTD, including hypoglycemia, hyperthermia,

Formation of the brain and spinal cord begins with the development of the neural tube through the embryonic process of neurulation. The neural tube is the origin of the brain and spinal cord. The process of neurulation, has two separate phases in

Primary neurulation occurs in the third and fourth weeks of development, during which the flat layer of ectodermal cells is transformed into a hollow tube. On the 18th day of fertilization, the neural plate is formed by a thickening of the embryonal midline dorsal ectoderm. The neural plate develops from the cranial end of the embryo moving toward the caudal end. *This sentence is deleted ---*Then, the edges of the neural plate move upward to form the neural fold---. On 19th day, the border of the neural plate becomes elevated and folds longitudinally from the head to the tail, which results in the formation of a neural groove. By the 23rd day, the folds get merged and make the neural tube which is open at both ends. "Closure," a process in which both open ends of the neural tube (neuropores) are closed, occurs on the 26th and 28th day of gestational age in rostral and caudal ends, respectively. This neural tube closure is initiated at the hindbrain/cervical boundary (Closure 1).

mammalian embryos, termed primary and secondary neurulation [32].

**4.1 Genetics of congenital CNS anomalies**

anomalies in the cases of NTD.

valproic acid, and cytochalasins.

**4.2 Embryologic formation of neural tube**

anomalies [31].

**110**

#### **5.1 Laboratory-based diagnosis of NTDs**

Maternal serum alpha-fetoprotein blood levels are used for the screening of CNS anomalies in the fetus, in addition to magnetic resonance imaging or ultrasonography [36, 37].

#### **5.2 Imaging-based diagnosis of NTDs**

Fetal magnetic resonance imaging (MRI) was first reported in 1983 [38]. In the late 1990s, fast-sequence MRI was introduced (which eliminated the need for maternal sedation), and fetal MRI was preferred by clinicians [39]. Many studies have reported MRI to be a more accurate technique for diagnosing fetal CNS anomalies compared to ultrasound [40, 41].

In 2014, a systematic review was conducted by Rossi et al., which included 13 original articles and 710 fetuses. This report documented that in addition to confirming the US findings in 65.4% of cases, MRI provides additional information (especially about midline anomalies) in 22.1% of cases [37]. Overall, MRI was able to identify CNS anomalies in 18.4% of cases. Ultrasound was more accurate than MRI in 2% of cases. In 30% of cases, the MRI findings of fetal visualization were

different from US findings enough to change the management. They reported a false-positive rate of 2.5% in diagnosing conditions like midline anomalies, hemorrhage, and cell-proliferation disorders by MRI. It is suggested that clinicians should combine fetal MRI with 2-or 3-D-US in order to reduce false-positive diagnosis and increase the sensitivity [42].

It is known that the placenta plays a key role in the fetal development and in protecting the fetus against the maternal immune system and pathogens. There are correlations between placental dysfunction and neurodevelopmental injury [43, 44], and placental ischemia and inflammation can damage the developing fetal CNS. Fetal MRI provides the opportunity to accurately assess *invivo* fetal placental and brain function [45]. In intrauterine growth restricted conditions, placentas have decreased volume as well as lower apparent diffusion coefficient (ADC) values [46–48]. Shapira-Zaltsberg et al., in an interesting study in 2017, evaluated the MRI characteristics of the placenta in fetuses with and without CNS anomalies. They concluded that in diffusion-weighted imaging (DWI) of fetal MRI, restricted diffusion in placenta as well as reduced ADC values are accompanied with fetal CNS abnormalities [43].
