Anencephaly: Lateral View of Fetal Developmental Abnormality in Neural Tube Defects

The image depicts a lateral (side) view of an anencephalic fetus, revealing the characteristic absence of the cranial vault and cerebral hemispheres. Anencephaly represents one of the most severe forms of neural tube defects, occurring when the rostral (head) end of the neural tube fails to close during early embryonic development. This devastating congenital malformation is incompatible with prolonged survival, with most affected newborns surviving only hours to days after birth. The lateral perspective provides medical professionals with important diagnostic visualization of the craniofacial profile typical in anencephaly, showing the absent cranial vault, exposed rudimentary brain tissue, and distinctive facial features that result from this profound developmental failure.

The image does not contain labeled anatomical structures. However, several key anatomical features characteristic of anencephaly are clearly visible:

Absent Cranial Vault: The most striking feature is the complete absence of the calvarium (skull cap). Instead of the normal rounded cranial vault, the superior aspect of the head displays exposed rudimentary neural tissue. This absence results from the failure of the neural tube closure, which prevents normal induction of overlying bone formation.

Rudimentary Brain Tissue: The reddish tissue visible at the top of the head represents rudimentary neural tissue that failed to develop into normal brain structures. This tissue lacks the organized architecture of a normal brain and consists primarily of vascular membranes and neural remnants.

Facial Profile: The profile shows the characteristic “frog-like” facial appearance with a sloping forehead and prominent eyes. The face itself has developed relatively normally below the level of the orbits, which is consistent with the pattern of failure in rostral neural tube closure.

Ear Formation: The ear is visible and appears relatively well-formed, though possibly low-set. This reflects the selective nature of the developmental failure, which primarily affects structures derived from the rostral neural tube while allowing relatively normal development of other craniofacial structures.

Upper Limbs: The image shows well-developed upper limbs with distinguishable fingers, demonstrating that limb development proceeds normally despite the severe cranial defect. This highlights the localized nature of the neural tube closure defect in anencephaly.

Pathophysiology and Embryology of Anencephaly

Anencephaly results from a fundamental failure in early embryonic development. Understanding the embryological basis helps clarify the characteristic features visible in the image. Neural tube formation occurs during the third and fourth weeks of gestation, through a process called neurulation. When this process is disrupted at the cranial end, anencephaly results.

The neural tube forms through the folding of the neural plate, which begins in the middle and proceeds bidirectionally toward both the cranial and caudal ends. By day 28 of gestation, the neural tube should be completely closed. In anencephaly, the cranial neuropore fails to close, leaving the developing brain exposed to amniotic fluid. This exposure leads to degeneration of the developing cerebral hemispheres and prevents the formation of the overlying skull bones.

The prosencephalon (forebrain) and mesencephalon (midbrain) are most severely affected in anencephaly, while the rhombencephalon (hindbrain) may be partially preserved. This explains why basic brainstem functions like cardiac and respiratory regulation may initially be present in anencephalic newborns despite the absence of higher brain structures.

Risk Factors and Etiology

Multiple factors contribute to the development of anencephaly, reflecting a complex interplay between genetic susceptibility and environmental influences:

• Folate Deficiency: Inadequate maternal folic acid levels represent the most significant modifiable risk factor. Neural tube closure requires adequate folate for rapid cellular division and DNA synthesis.
• Genetic Factors: Mutations in genes involved in folate metabolism, such as MTHFR (methylenetetrahydrofolate reductase), increase susceptibility. The recurrence risk in families with one affected pregnancy is approximately 3-5%, suggesting genetic contributions.
• Environmental Teratogens: Maternal exposure to certain anticonvulsant medications, particularly valproic acid, significantly increases risk. Other teratogens include hyperthermia and some mycotoxins.
• Maternal Conditions: Pre-gestational diabetes mellitus and obesity correlate with increased risk, though the exact mechanisms remain incompletely understood.

Epidemiology and Public Health Impacts

Anencephaly affects approximately 1 in 1,000 pregnancies worldwide, though many cases end in spontaneous abortion. The incidence varies significantly by geographic region and ethnicity, reflecting differences in both genetic susceptibility and public health measures.

The introduction of folate fortification programs in many countries has dramatically reduced the incidence of neural tube defects. In the United States, mandatory folic acid fortification of enriched cereal grain products began in 1998, resulting in a 28% reduction in anencephaly rates. Similar programs worldwide have demonstrated comparable success, highlighting the effectiveness of this public health intervention.

Despite these advances, disparities persist in anencephaly rates, with higher incidence in regions with:

• Limited access to prenatal care
• Absence of food fortification programs
• Lower socioeconomic status
• Limited knowledge about periconceptional folic acid supplementation

These disparities underscore the ongoing need for global public health initiatives targeting neural tube defect prevention.

Prenatal Diagnosis and Screening

Modern prenatal care has dramatically improved early detection of anencephaly. Several complementary approaches enable timely diagnosis:

Maternal Serum Alpha-Fetoprotein (MSAFP)

Elevated levels of alpha-fetoprotein in maternal serum strongly suggest open neural tube defects. This screening test is typically performed between 15-20 weeks of gestation. In anencephaly, MSAFP levels are markedly elevated, often exceeding 4.0 multiples of the median (MoM).

Alpha-fetoprotein is produced by the fetal liver and yolk sac. The absence of the protective skull in anencephaly allows this protein to leak into the amniotic fluid and subsequently into maternal circulation, explaining the elevated levels. While not diagnostic alone, elevated MSAFP warrants further investigation with targeted ultrasound.

Ultrasound Examination

Anencephaly can be reliably diagnosed by ultrasound as early as 11-14 weeks of gestation, with nearly 100% sensitivity by the second trimester. Characteristic sonographic findings mirror the features visible in the specimen image:

• Absence of the cranial vault above the orbital ridge
• Exposed neural tissue with the “frog eye” sign
• Abnormal facial profile with absent forehead
• Polyhydramnios (excess amniotic fluid) in later pregnancy

The distinctive appearance makes anencephaly one of the most readily diagnosable congenital anomalies on prenatal ultrasound, allowing for early counseling and management planning.

Clinical Management and Ethical Considerations

The universally fatal nature of anencephaly presents unique challenges in clinical management. Several approaches must be considered:

Obstetric Management

When anencephaly is diagnosed prenatally, healthcare providers must compassionately discuss several management options with the family:

• Pregnancy termination, depending on gestational age and local regulations
• Continuation of pregnancy with standard obstetric care
• Continuation of pregnancy with palliative care planning for the neonate

If the pregnancy continues, vaginal delivery is typically recommended, as cesarean delivery offers no benefit to the fetus and increases maternal morbidity. However, the abnormal head shape may occasionally complicate vaginal delivery, requiring careful obstetric management.

Neonatal Palliative Care

For live-born anencephalic infants, the focus shifts to palliative care. This approach emphasizes:

• Comfort measures to minimize suffering
• Family-centered care that honors parental wishes
• Support for bonding and memory-making
• Appropriate symptom management
• Dignified end-of-life care

Most anencephalic newborns survive only hours to days, though rare cases of survival for weeks or months have been reported. Throughout this time, the medical team must provide ongoing support to the family while managing the infant’s basic needs.

Organ Donation Considerations

Some families may explore organ donation from anencephalic infants. This presents complex ethical and practical challenges:

• The dead donor rule requires declaration of death before organ procurement
• Anencephalic infants may have functioning brainstems, complicating brain death determination
• Protocols exist in some regions for donation after cardiac death
• Technical challenges include organ size matching and quality preservation

Medical teams must navigate these considerations with sensitivity while upholding ethical standards and respecting family wishes.

Prevention Strategies

The most effective intervention for neural tube defects is primary prevention through periconceptional folic acid supplementation. Public health initiatives include:

• Daily supplementation with 400-800 μg of folic acid for all women of childbearing potential
• Higher doses (4 mg daily) for women with prior neural tube defect-affected pregnancies
• Food fortification programs adding folic acid to grain products
• Enhanced supplementation for women taking medications that interfere with folate metabolism

These measures have dramatically reduced the incidence of neural tube defects, with studies demonstrating up to 70% reduction following implementation of folic acid fortification programs. This success emphasizes the critical importance of preconception care and counseling.

Genetic Counseling and Recurrence Risk

Families with a history of anencephaly require comprehensive genetic counseling regarding recurrence risk in future pregnancies. Key considerations include:

• 3-5% recurrence risk after one affected pregnancy
• 10-15% risk after two affected pregnancies
• Importance of high-dose folic acid supplementation (4 mg daily) beginning at least one month before conception
• Consideration of genetic testing for folate metabolism disorders
• Planning for intensive prenatal surveillance in subsequent pregnancies

This counseling helps families make informed reproductive decisions while implementing appropriate preventive measures to reduce recurrence risk.

The lateral view of an anencephalic fetus presented in this image serves as a powerful educational tool for understanding the profound structural abnormalities associated with neural tube defects. Through continued research, public health initiatives, and compassionate clinical care, the medical community strives to reduce the incidence of these devastating conditions while providing optimal support for affected families.

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1. Anencephaly: Lateral Fetal View Revealing Characteristic Neural Tube Defect Anatomy
2. Neural Tube Defects: Anatomical Analysis of Anencephaly in Lateral Fetal Perspective
3. Understanding Anencephalic Anatomy: Comprehensive Guide to Fetal Neural Tube Malformations
4. Embryological Basis of Anencephaly: Analyzing Lateral Profile Features in Fetal Specimens
5. Congenital Anencephaly: Detailed Examination of Lateral Fetal Presentation for Medical Education

anencephaly, neural tube defect, folate deficiency, congenital malformation, prenatal diagnosis, alpha-fetoprotein, craniofacial development, embryology, neurulation, folic acid, MTHFR gene, maternal serum screening, ultrasound diagnosis, perinatal palliative care, neonatal management, prosencephalon, rhombencephalon, brain development, calvarium absence, genetic counseling