Development of Nervous System — MCQs

10 questions

A neonate presents with failure to pass meconium. The structure absent in the pathology lies in which of the following layers?

Which of the following statements concerning spina bifida is True?

Which of the following is not a known cause of neuroregression in children?

At 30 days of intrauterine life, what is the expected developmental milestone?

Which of the following is the MOST accurate test for detecting neural tube defects?

Deficiency of which vitamin during early pregnancy will result in neural tube defect?

Which malformation is associated with mutations in the HOX gene?

Which tumor arises from embryonic neural cells?

A 25-year-old pregnant woman, at 18 weeks of gestation, undergoes a routine ultrasound scan. The ultrasound images provided show below. Based on the imaging findings, what is the most likely diagnosis?

Q10

All the following features are seen in neurons from dorsal root ganglia, EXCEPT:

Development of Nervous System Indian Medical PG Practice Questions and MCQs

Question 1: A neonate presents with failure to pass meconium. The structure absent in the pathology lies in which of the following layers?

A. A, B
B. B, C
C. C, D (Correct Answer)
D. A, D
E. B, D

Explanation: ***C, D*** - The neonate's symptom of **failure to pass meconium** is characteristic of **Hirschsprung disease**, which is caused by the absence of **ganglion cells** in the distal colon. - The missing ganglion cells are typically found in the **submucosal (Meissner) plexus** and the **myenteric (Auerbach) plexus**, corresponding to layers C and D in the provided image. *A, B* - Layer A represents the **mucosa** (specifically the glandular epithelium), and layer B represents the **lamina propria** or potentially the muscularis mucosa. - These layers do not primarily house the ganglion cells implicated in Hirschsprung disease. *B, C* - Layer B is the **lamina propria** or **muscularis mucosa**, and layer C is the **submucosa**. - While the submucosa (C) contains the Meissner plexus, layer B does not contain ganglion cells relevant to this pathology. *B, D* - Layer B is the **lamina propria/muscularis mucosa**, and layer D is the **muscularis propria**. - While the myenteric plexus (associated with D) is affected in Hirschsprung disease, layer B does not contain ganglion cells, and this option incorrectly excludes the submucosal plexus (layer C), which also contains ganglion cells that are absent in this condition. *A, D* - Layer A is the **mucosa**, and layer D is the **muscularis propria** (outer muscle layer). - The mucosa (A) does not contain the ganglion cells, while the myenteric plexus (associated with D) is affected, but this option incorrectly includes A and omits the submucosal plexus (C).

Question 2: Which of the following statements concerning spina bifida is True?

A. Spina bifida occulta occurs most often at L5-S1 level (Correct Answer)
B. Chromosomal abnormalities can be identified in approximately 50% of patients
C. A myelomeningocele is the most common type of spina bifida
D. Additional congenital abnormalities are rare findings

Explanation: **Spina bifida occulta occurs most often at L5-S1 level** - **Spina bifida occulta** is the mildest form of spina bifida, characterized by an incomplete closure of the vertebral arch without protrusion of the spinal cord or meninges. - The most common location for spina bifida occulta is the **L5-S1 vertebral level**, which often presents as a skin dimple, tuft of hair, or discolored patch in the lumbar region. *Chromosomal abnormalities can be identified in approximately 50% of patients* - **Chromosomal abnormalities** are found in a minority of patients with spina bifida, typically less than 10%, when evaluating for genetic causes. - While single-gene mutations or environmental factors contribute, spina bifida is most often considered a **multifactorial condition** rather than solely chromosomal. *A myelomeningocele is the most common type of spina bifida* - A **myelomeningocele** is the most severe and a common type of spina bifida where the spinal cord and meninges protrude through an opening in the spine. - However, **spina bifida occulta** is statistically the most common type overall, though it is often asymptomatic and may go undiagnosed. *Additional congenital abnormalities are rare findings* - **Additional congenital abnormalities** are not rare; they are frequently associated with spina bifida, particularly with myelomeningocele. - These can include **hydrocephalus**, **Chiari malformations**, urinary tract anomalies, and orthopedic issues like clubfoot, reflecting a systemic developmental disruption.

Question 3: Which of the following is not a known cause of neuroregression in children?

A. Vitamin B12 deficiency
B. Ataxia telangiectasia
C. ADHD (Correct Answer)
D. Wilson's disease

Explanation: ***ADHD*** - **Attention-deficit/hyperactivity disorder (ADHD)** is a neurodevelopmental disorder characterized by persistent patterns of inattention, hyperactivity, and impulsivity. It is **not** a cause of neuroregression. - While ADHD can impact cognitive and behavioral functioning, it does not involve a loss of previously acquired developmental milestones or skills. *Wilson's disease* - **Wilson's disease** is an inherited disorder that causes **copper accumulation** in organs, particularly the liver and brain. - Neurological symptoms, including **neuroregression**, can occur due to copper toxicity in the central nervous system. *Vitamin B12 deficiency* - **Vitamin B12 deficiency** can lead to neurological complications such as **subacute combined degeneration** of the spinal cord and peripheral neuropathy. - In children, severe or prolonged deficiency can impair brain development and lead to **developmental regression**. *Ataxia telangiectasia* - **Ataxia telangiectasia** is a rare, neurodegenerative, inherited disease that affects multiple body systems. - It is characterized by progressive **cerebellar ataxia**, leading to **neuroregression** and intellectual disability over time.

Question 4: At 30 days of intrauterine life, what is the expected developmental milestone?

A. Optic vesicle appears (Correct Answer)
B. Heart starts beating
C. Cerebellum develops
D. Pinna appears

Explanation: Optic vesicle appears - The **optic vesicle** is an outpocketing from the diencephalon that appears around **day 22-28** of development. - At approximately **30 days** (end of 4th week/early 5th week), the optic vesicle is actively present and beginning to invaginate to form the optic cup. - Among the given options, this represents the developmental structure most characteristically associated with the **late 4th week/30-day timeframe** in embryology milestones. *Heart starts beating* - The primitive heart tube begins to beat around **day 22-23** of gestation. - By 30 days, the heart has already been beating for over a week, making this an earlier milestone rather than one expected "at" 30 days. *Cerebellum develops* - The cerebellum develops later, primarily during the **second and third months** (weeks 8-12) of gestation as the metencephalon differentiates. - Major cerebellar development occurs well after 30 days. *Pinna appears* - The external ear (pinna) begins forming around the **sixth week** (~42 days) from six auricular hillocks.

Question 5: Which of the following is the MOST accurate test for detecting neural tube defects?

A. USG (Correct Answer)
B. Placentography
C. Chromosomal analysis
D. Amniocentesis

Explanation: ***USG (Ultrasound)*** - **High-resolution ultrasound** is the **gold standard and most accurate imaging modality** for detecting **neural tube defects (NTDs)** due to its ability to directly visualize anatomical structures of the fetus. - **Diagnostic accuracy**: Detection rate >95% for anencephaly and 80-90% for open spina bifida with targeted anomaly scan at 18-20 weeks. - Can identify specific features such as **lemon sign** (frontal bone scalloping), **banana sign** (cerebellar compression), direct visualization of **spina bifida**, **anencephaly**, or **encephalocele**. - **Non-invasive, safe, and widely available**, making it the primary diagnostic tool in clinical practice. *Amniocentesis* - **Amniocentesis** measures **alpha-fetoprotein (AFP)** and **acetylcholinesterase (AChE)** in amniotic fluid, which are elevated in open NTDs. - While highly accurate as a **confirmatory test** (near 99% sensitivity with both markers), it is **invasive** with risk of miscarriage (0.1-0.3%). - Used primarily when ultrasound findings are **equivocal** or for **biochemical confirmation**, not as the first-line diagnostic test. - In modern practice, ultrasound has largely replaced amniocentesis for NTD diagnosis due to superior imaging technology. *Chromosomal analysis* - **Chromosomal analysis** (karyotyping) detects **chromosomal abnormalities** like trisomies (Down syndrome, Edwards syndrome). - NTDs are **structural malformations**, not chromosomal abnormalities, though some chromosomal disorders may have associated structural defects. - Does not directly diagnose NTDs. *Placentography* - **Placentography** is used to localize the **placenta** in cases of suspected **placenta previa** or for guiding invasive procedures. - Provides no information about **fetal anatomy** and is not used for detecting NTDs.

Question 6: Deficiency of which vitamin during early pregnancy will result in neural tube defect?

A. Folic acid (Correct Answer)
B. Iron
C. Cyanocobalamine
D. Vitamin E

Explanation: ***Folic acid*** - **Folic acid** (vitamin B9) is crucial for **neural tube closure** during the first 28 days of embryonic development. - Deficiency leads to conditions like **spina bifida** and **anencephaly**. - **Periconceptional supplementation** with 400-800 mcg daily is recommended to prevent neural tube defects. *Iron* - **Iron** is essential for **hemoglobin synthesis** and fetal growth, but its deficiency does not directly cause neural tube defects. - Iron deficiency in pregnancy can lead to **maternal anemia** and premature birth. *Cyanocobalamine* - **Cyanocobalamine** (vitamin B12) is involved in DNA synthesis and neurological function, but its direct link to neural tube defects is not as strong as folic acid. - Severe B12 deficiency can cause **megaloblastic anemia** and neurological issues. *Vitamin E* - **Vitamin E** is a fat-soluble antioxidant that protects cell membranes from oxidative damage. - While important for overall health during pregnancy, it does not play a specific role in neural tube closure. - Deficiency is rare and does not cause neural tube defects.

Question 7: Which malformation is associated with mutations in the HOX gene?

A. Polysyndactyly (Correct Answer)
B. Holoprosencephaly
C. Mayer Rokitansky syndrome
D. Gorlin syndrome

Explanation: ***Polysyndactyly*** - The **HOX gene** plays a critical role in limb development and is associated with the malformation of **polysyndactyly**, which is characterized by extra fingers or toes [1]. - This condition is due to the disruption of the normal **patterning** during limb formation, directly involving the action of HOX genes [1]. *Gorlin syndrome* - Gorlin syndrome is primarily caused by mutations in the **PTCH1 gene**, linked to **basal cell carcinoma** and other abnormalities. - It does not involve HOX gene mutations, hence is **not** related to limb malformations. *Holoprosencephaly* - Holoprosencephaly is a developmental condition often linked to **chromosomal anomalies** and abnormal embryonic development, **not specifically** HOX gene mutations. - It refers to the incomplete separation of the forebrain, distinct from the **limb malformations** associated with HOX genes. *Mayer Rokitansky syndrome* - Mayer-Rokitansky syndrome involves **agenesis** or **hypoplasia** of the uterus and upper two-thirds of the vagina, which is due to other genetic factors. - This condition is not related to the functions of the **HOX genes** in limb or skeletal development. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, p. 1186.

Question 8: Which tumor arises from embryonic neural cells?

A. Medulloblastoma (Correct Answer)
B. Fibrous astrocytoma
C. Neuroglioma
D. Ependymoma

Explanation: ***Medulloblastoma*** - This tumor arises from **embryonic neural cells** in the **cerebellum**. - It is a highly malignant **brain tumor** most commonly found in children [1]. *Fibrous astrocytoma* - This is a type of **glioma** that arises from **mature astrocytes**, not embryonic neural cells. - It typically occurs in adults and can be found in various locations within the brain. *Neuroglioma* - This is a broad term that refers to **tumors of neuroglial origin**, meaning they arise from glial cells. - It does not specifically refer to a tumor originating from embryonic neural cells. *Ependymoma* - This tumor arises from **ependymal cells**, which line the **ventricles** and **spinal canal**. - While these are technically neural cells, they are more differentiated than the embryonic neural cells that give rise to medulloblastoma. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1314-1315.

Question 9: A 25-year-old pregnant woman, at 18 weeks of gestation, undergoes a routine ultrasound scan. The ultrasound images provided show below. Based on the imaging findings, what is the most likely diagnosis?

A. Spina bifida (Correct Answer)
B. Anencephaly
C. Encephalocele
D. Holoprosencephaly
E. Iniencephaly

Explanation: ***Spina bifida*** - The ultrasound image shows a **defect in the posterior elements of the fetal spine**, with characteristic splaying or widening of the vertebral arches. - This is a **neural tube defect** resulting from incomplete closure of the spinal column during embryonic development. - Associated findings on prenatal ultrasound may include the **"lemon sign"** (scalloping of frontal bones) and **"banana sign"** (abnormal cerebellar shape). - Spina bifida is typically detected on **second-trimester anatomy scan** (18-20 weeks). *Anencephaly* - This condition involves the **absence of a major portion of the brain, skull, and scalp** due to failure of anterior neural tube closure. - On ultrasound, anencephaly presents with **absent calvarium above the orbits** and absent cerebral hemispheres, which is distinctly different from a spinal defect. - This would be a **cranial abnormality**, not a spinal column defect. *Encephalocele* - An **encephalocele** is a protrusion of brain tissue and meninges through a defect in the skull, most commonly at the **occipital region**. - On ultrasound, this appears as a **cranial mass** extending beyond the skull contour, not a spinal defect. *Holoprosencephaly* - This condition results from **failure of forebrain (prosencephalon) to divide properly** into two hemispheres. - Ultrasound findings include **single ventricle**, fused thalami, and absent midline structures, often with associated **facial anomalies**. - The imaging would show **brain abnormalities**, not spinal column defects. *Iniencephaly* - This is a rare **neural tube defect** characterized by extreme retroflexion of the head with severe spinal defects in the cervical and thoracic regions. - On ultrasound, iniencephaly shows the fetal head in extreme **hyperextension** with the face looking upward, creating a characteristic "stargazing" appearance. - This differs from the typical spinal defect pattern seen in spina bifida.

Question 10: All the following features are seen in neurons from dorsal root ganglia, EXCEPT:

A. They are multipolar (Correct Answer)
B. They are derived from neural crest cells
C. They have eccentrically located nuclei
D. They contain lipofuscin granules

Explanation: ***They are multipolar*** - Dorsal root ganglia (DRG) neurons are typically **pseudounipolar**, meaning they have a single process that branches into two (peripheral and central) rather than multiple dendrites and an axon [1]. - **Multipolar neurons** are characteristic of motor neurons and interneurons in the central nervous system, not DRG sensory neurons [1]. *They contain lipofuscin granules* - **Lipofuscin granules** are common in long-lived, post-mitotic cells like neurons and are considered "wear and tear" pigments, accumulating with age. - Their presence in DRG neurons is a normal finding and reflects the neuron's metabolic activity over time. *They have eccentrically located nuclei* - While not universally present in all DRG neurons, an **eccentrically located nucleus** is a common histological feature of certain types of DRG neurons, particularly larger ones. - This feature helps distinguish them from other neuron types and can be accentuated by the large amount of cytoplasm in these cells. *They are derived from neural crest cells* - All sensory neurons of the DRG, along with other components like Schwann cells and sympathetic ganglia, originate from **neural crest cells**. - This developmental origin is a fundamental characteristic of DRG neurons, distinguishing them from CNS neurons derived from the neural tube.

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