Neural Tube Defects — MCQs
What condition is associated with the sign seen in the given USG?
Which is the initial site of closure of the neural tube in embryological life?
Common deformity in Chiari II malformation is -
Which of the following tests on amniotic fluid is most useful in distinguishing between open neural tube defects and ventral wall defects in a fetus?
Which one of the following biochemical parameters is the most sensitive to detect open spina bifida?
All of the following are neural tube defects except:
In pregnancy, neural tube defects arise in the fetus due to a deficiency of which specific vitamin in the mother?
Which of the following statements about encephalocoele is false?
A young child with recurrent bacterial meningitis should be clinically evaluated for the presence of
A 1-year-old child was brought to the outpatient department with a soft and compressible swelling on the nose that increases on coughing. Which of the following is most likely the diagnosis?
Neural Tube Defects Indian Medical PG Practice Questions and MCQs
Question 1: What condition is associated with the sign seen in the given USG?
- A. Anencephaly
- B. Spina bifida (Correct Answer)
- C. Dandy-Walker malformation
- D. Encephalocele
Explanation: ***Spina bifida*** - The ultrasound image displays the **"lemon sign"** (frontal bone indentation), which is a classic indicator of **spina bifida** on antenatal ultrasound. - The lemon sign is caused by **scalloping of the frontal bones** due to caudal displacement of brain tissue (Arnold-Chiari malformation type II) secondary to an open spinal defect. - This sign is most commonly seen in the **second trimester** and is associated with neural tube defects. *Anencephaly* - **Anencephaly** presents with absence of the cranial vault and cerebral hemispheres on ultrasound. - The characteristic finding is the **"frog-eye appearance"** with protruding orbits, not frontal bone scalloping. - This is incompatible with life and has a distinctly different ultrasound appearance. *Dandy-Walker malformation* - **Dandy-Walker malformation** shows an enlarged posterior fossa with cystic dilatation of the fourth ventricle and hypoplasia of the cerebellar vermis. - It may present with the **"banana sign"** (cerebellar compression), but not the lemon sign. - This is a posterior fossa abnormality, not associated with frontal bone changes. *Encephalocele* - **Encephalocele** presents as a herniation of brain tissue and meninges through a cranial defect, typically occipital. - Ultrasound shows a **cystic mass protruding from the skull**, not frontal bone indentation. - While it's a neural tube defect, it has a different ultrasound appearance than the lemon sign.
Question 2: Which is the initial site of closure of the neural tube in embryological life?
- A. Caudal end
- B. Cranial end
- C. Midpoint
- D. None of the options (Correct Answer)
Explanation: The initial closure of the neural tube begins at **Closure 1**, located at the **cervical/hindbrain boundary region** (approximately at the level of the 4th somite, future cervical vertebrae 1-3). This occurs around **day 22-23** of embryonic development. Neural tube closure follows a **multi-site initiation model** with 5 distinct closure points (Closures 1-5), not at the simple cranial, caudal, or midpoint locations listed. *Cranial end* - The **rostral (anterior) neuropore** at the cranial end closes **last** among the cranial structures, around day 25-26. - This is a site of **late closure**, not initial closure. - Failure results in **anencephaly**. *Caudal end* - The **caudal (posterior) neuropore** closes **last** of all, around day 27-28. - This is the **final closure point**, not the initial site. - Failure results in **spina bifida**. *Midpoint* - While Closure 1 occurs roughly in the "middle" of the future neural tube (cervical region), this is not a simple anatomical midpoint. - The closure process involves multiple initiation sites with bidirectional zipper-like progression, not a single midpoint origin.
Question 3: Common deformity in Chiari II malformation is -
- A. Syringomyelia (Correct Answer)
- B. Hydrocephalus
- C. Meningo myelocele
- D. All of the options
Explanation: ***Syringomyelia*** - **Syringomyelia** is a common deformity associated with Chiari II malformation, characterized by a **fluid-filled cyst (syrinx)** within the spinal cord. - This cyst can expand and damage the spinal cord, leading to symptoms such as **pain**, **weakness**, and **sensory deficits**. *Hydrocephalus* - While **hydrocephalus** (excess CSF in the brain) is frequently seen with Chiari II malformation, it is a **complication** or associated condition rather than a specific deformity caused by the malformation itself [1]. - It often results from the **obstruction of CSF flow** due to the displacement of hindbrain structures [1]. *Meningo myelocele* - **Meningomyelocele** is a severe form of **spina bifida** where the spinal cord and its coverings protrude through an opening in the spine. - It is often associated with Chiari II malformation, as they share a common developmental origin, but it is a primary **neural tube defect**, not a deformity specifically *caused by* Chiari II. *All of the options* - While all three conditions (syringomyelia, hydrocephalus, and meningomyelocele) are often seen in conjunction with Chiari II malformation, only **syringomyelia** is directly considered a "deformity" or direct consequence resulting from the herniation of brain tissue characteristic of Chiari II. - Hydrocephalus and meningomyelocele are either associated conditions or complications, rather than a direct structural deformity of the brainstem and cerebellum.
Question 4: Which of the following tests on amniotic fluid is most useful in distinguishing between open neural tube defects and ventral wall defects in a fetus?
- A. Carcinoembryonic antigen
- B. Alpha-fetoprotein
- C. Sphingomyelin
- D. Acetylcholinesterase (Correct Answer)
Explanation: ***Acetylcholinesterase*** - **Acetylcholinesterase (AChE)** is highly specific to neural tissue and its presence in amniotic fluid, combined with elevated AFP, is highly indicative of an **open neural tube defect (NTD)**. - While AFP is elevated in both NTDs and ventral wall defects, **AChE** helps differentiate by confirming neural tissue exposure. *Carcinoembryonic antigen* - **Carcinoembryonic antigen (CEA)** is a tumor marker primarily used in the diagnosis and monitoring of certain cancers, particularly colorectal cancer. - It has no established role in the prenatal diagnosis or differentiation of neural tube defects or ventral wall defects. *Sphingomyelin* - **Sphingomyelin** is a component of pulmonary surfactant and is measured to assess fetal lung maturity, usually in conjunction with lecithin as the **L/S ratio**. - This test is not used for the diagnosis or differentiation of structural birth defects like neural tube defects or ventral wall defects. *Alpha-fetoprotein* - **Alpha-fetoprotein (AFP)** is elevated in maternal serum and amniotic fluid in both **open neural tube defects** and **ventral wall defects** (e.g., gastroschisis, omphalocele). - While useful for screening, **AFP alone cannot distinguish** between these two conditions, as it is non-specific for the type of open defect.
Question 5: Which one of the following biochemical parameters is the most sensitive to detect open spina bifida?
- A. Maternal serum alpha fetoprotein.
- B. Amniotic fluid alpha fetoprotein.
- C. Amniotic fluid acetyl cholinesterase. (Correct Answer)
- D. Amniotic fluid hexosaminidase.
Explanation: ***Amniotic fluid acetylcholinesterase*** - **Amniotic fluid acetylcholinesterase (AChE)** is highly specific and sensitive for detecting **open neural tube defects (NTDs)**, such as open spina bifida. - The enzyme leaks directly from the exposed neural tissue into the **amniotic fluid**, making its presence a strong indicator of the defect. *Maternal serum alpha fetoprotein* - **Maternal serum alpha-fetoprotein (MSAFP)** is a screening tool, but it is not as specific as amniotic fluid markers. - Elevated MSAFP can be caused by various other conditions, including **multiple gestations** or **abdominal wall defects**, leading to higher false-positive rates. *Amniotic fluid alpha fetoprotein* - While **amniotic fluid alpha-fetoprotein (AFAFP)** is elevated in open neural tube defects, it is less specific than **AChE**. - AFAFP can also be elevated in other conditions like **gastroschisis** or **omphalocele**, making AChE a more definitive diagnostic marker. *Amniotic fluid hexosaminidase* - **Hexosaminidase** is an enzyme that is elevated in conditions like **Tay-Sachs disease**, a lysosomal storage disorder. - It is **not used as a biochemical marker** for the detection of open spina bifida or other neural tube defects.
Question 6: All of the following are neural tube defects except:
- A. Holoprosencephaly (Correct Answer)
- B. Encephalocele
- C. Myelomeningocele
- D. Anencephaly
Explanation: ***Holoprosencephaly*** - This condition results from the **failure of the prosencephalon (forebrain)** to properly divide into two hemispheres, often leading to facial abnormalities. - It is considered a **forebrain malformation**, distinct from neural tube closure defects. *Encephalocele* - An encephalocele is a **neural tube defect** characterized by the protrusion of brain tissue and meninges through an opening in the skull. - It results from the **incomplete closure of the neural tube** during embryonic development. *Myelomeningocele* - Myelomeningocele is a severe form of **spina bifida**, a neural tube defect where the spinal cord and meninges protrude through an opening in the spine [2]. - This defect arises from the **failure of the neural tube to close completely** in the caudal region [1]. *Anencephaly* - Anencephaly is a lethal **neural tube defect** characterized by the absence of a major portion of the brain, skull, and scalp [3]. - It occurs due to the **failure of the cranial end of the neural tube to close** [3].
Question 7: In pregnancy, neural tube defects arise in the fetus due to a deficiency of which specific vitamin in the mother?
- A. Folic Acid (Correct Answer)
- B. Vitamin A
- C. Vitamin C
- D. Vitamin D
Explanation: ***Folic Acid*** - Deficiency of **folic acid (Vitamin B9)** during early pregnancy is a well-established cause of **neural tube defects (NTDs)** in the fetus. - Adequate folate intake is crucial for proper **neural tube closure**, which occurs at 3-4 weeks gestation. *Vitamin D* - **Vitamin D deficiency** is linked to bone health issues, such as **rickets** in children and **osteomalacia** in adults, and can impact immune function. - It is not directly associated with the development of **neural tube defects**. *Vitamin A* - **Vitamin A** is essential for vision, immune function, and cell growth, but both its **deficiency** and **excess** can cause birth defects. - Excessive intake of preformed Vitamin A (retinol) is **teratogenic** (e.g., causing craniofacial, cardiac, and central nervous system anomalies), but deficiency does not typically cause neural tube defects. *Vitamin C* - **Vitamin C** is vital for collagen synthesis, wound healing, and acts as an antioxidant. - Its deficiency causes **scurvy**, characterized by weakened connective tissue, but is not implicated in neural tube defects.
Question 8: Which of the following statements about encephalocoele is false?
- A. It is a neural tube defect
- B. Common in the parietal region (Correct Answer)
- C. Can be associated with hydrocephalus
- D. It is protrusion of neural tissue through a defect
Explanation: ***Common in the parietal region*** - This statement is **false** because encephaloceles are **rarely found in the parietal region** (only 10-15% of cases). - **Occipital encephaloceles** are most common in Western populations (75-80%), while **frontal/sincipital encephaloceles** are most common in Southeast Asia including India (40-60%). - **Parietal encephaloceles** represent only a small minority of cases globally, making this statement incorrect. *It is a neural tube defect* - **Encephalocele** is indeed a type of **neural tube defect (NTD)**, resulting from incomplete closure of the neural tube during embryonic development. - Specifically, it involves a defect in the skull that allows for protrusion of brain tissue and/or meninges. *Can be associated with hydrocephalus* - **Hydrocephalus**, or the accumulation of cerebrospinal fluid in the brain, is a known complication and associated condition with encephaloceles. - The abnormal brain development and structural defects can disrupt normal CSF flow and absorption, particularly with posterior encephaloceles. *It is protrusion of neural tissue through a defect* - This is the defining characteristic of an **encephalocele**: the **herniation of intracranial contents**, such as brain tissue, meninges, or both, through a congenital **bony defect** in the skull. - The contents of the sac can vary (meninges only = meningocele; brain tissue included = meningoencephalocele), influencing clinical presentation and prognosis.
Question 9: A young child with recurrent bacterial meningitis should be clinically evaluated for the presence of
- A. Spina bifida occulta with a dermal sinus tract (Correct Answer)
- B. Hypoplastic left heart syndrome
- C. Syringomyelia of the lower cervical cord
- D. Holoprosencephaly
Explanation: ***Spina bifida occulta with a dermal sinus tract*** - A **dermal sinus tract** provides a direct pathway for skin flora to access deeper structures, including the **meninges**, leading to recurrent bacterial meningitis - This condition arises from incomplete closure of the neural tube and is often associated with cutaneous stigmata such as a **dimple, tuft of hair, or hemangioma** in the lumbosacral region - Clinical examination should focus on the **midline back** for these telltale signs - This is the **most common anatomical cause** of recurrent bacterial meningitis in children *Hypoplastic left heart syndrome* - This is a congenital heart defect resulting in an underdeveloped left side of the heart, leading to cyanosis and heart failure - It is not directly associated with an increased risk of recurrent bacterial meningitis - This is a **cardiac anomaly**, not a CNS communication defect *Syringomyelia of the lower cervical cord* - Syringomyelia involves the formation of a fluid-filled cavity (syrinx) within the spinal cord, typically causing neurological deficits related to pain, temperature sensation, and motor weakness - While it is a neurological condition, it does **not disrupt the meningeal barrier** and therefore does not explain recurrent bacterial meningitis - This is an **intramedullary lesion** without external communication *Holoprosencephaly* - This is a severe condition where the forebrain fails to develop into two hemispheres, leading to various craniofacial anomalies and significant neurological impairment - It is a developmental brain abnormality and is **not a cause** of recurrent bacterial meningitis - While severe, it does not create a pathway for bacterial entry into the CNS
Question 10: A 1-year-old child was brought to the outpatient department with a soft and compressible swelling on the nose that increases on coughing. Which of the following is most likely the diagnosis?
- A. Meningoencephalocele (Correct Answer)
- B. Arteriovenous malformation
- C. Lacrimal sac cyst
- D. Ethmoid cyst
Explanation: ***Meningoencephalocele*** - A soft, compressible nasal swelling that increases with **coughing** or **straining** is highly suggestive of a meningoencephalocele due to increased intracranial pressure. - This condition involves a **herniation of brain tissue** (encephalocele) and meninges through a bony defect, often in the nasal region. *Lacrimal sac cyst* - A lacrimal sac cyst would typically present as a swelling in the **medial canthal region** and is usually associated with **tear duct obstruction**, not directly on the nose increasing with coughing. - While soft, it is not usually **compressible** or affected by changes in intracranial pressure in the same way. *Arteriovenous malformation* - An arteriovenous malformation (AVM) would typically present as a **pulsatile** mass with a **bruit**, and might cause warmth or discoloration. - It would not characteristically increase in size with **coughing** as a result of intracranial pressure changes. *Ethmoid cyst* - An ethmoid cyst is a fluid-filled sac originating from the **ethmoid sinuses**. While it can cause nasal obstruction or swelling, it usually presents as a firm, non-pulsatile mass. - It would not typically exhibit **compressibility** with an increase in size when coughing, differentiating it from an intracranial connection.
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