Abdominal wall development US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Abdominal wall development. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Abdominal wall development US Medical PG Question 1: A 34-year-old woman comes to the emergency department because of a 2-hour history of abdominal pain, nausea, and vomiting that began an hour after she finished lunch. Examination shows abdominal guarding and rigidity; bowel sounds are reduced. Magnetic resonance cholangiopancreatography shows the dorsal pancreatic duct draining into the minor papilla and a separate smaller duct draining into the major papilla. The spleen is located anterior to the left kidney. A disruption of which of the following embryological processes is the most likely cause of this patient's imaging findings?
- A. Proliferation of mesenchyme in the dorsal mesentery
- B. Differentiation of the proximal hepatic diverticulum
- C. Fusion of the pancreatic buds (Correct Answer)
- D. Rotation of the midgut
- E. Rotation of the dorsal mesogastrium
Abdominal wall development Explanation: ***Fusion of the pancreatic buds***
- The imaging findings describe **pancreas divisum**, a congenital anomaly where the **dorsal and ventral pancreatic buds fail to fuse** completely.
- This leads to the dorsal pancreatic duct (containing most of the gland volume) draining through the **minor papilla**, which is functionally insufficient and can cause recurrent pancreatitis as seen in this patient with signs of peritonitis.
*Proliferation of mesenchyme in the dorsal mesentery*
- This process is primarily associated with the development of the **spleen**, which is derived from mesenchymal cells in the dorsal mesogastrium.
- While the spleen's position is mentioned, its development or abnormal position is not the cause of the pancreatic ductal anomaly described.
*Differentiation of the proximal hepatic diverticulum*
- The **hepatic diverticulum** gives rise to the liver, gallbladder, and biliary tree.
- Abnormalities in this process would lead to issues with these organs, not with the pancreatic ductal system.
*Rotation of the dorsal mesogastrium*
- The **dorsal mesogastrium** rotates during embryological development and gives rise to structures including the spleen and the greater omentum.
- While abnormal rotation could explain splenic malposition, it does not directly explain the pancreatic ductal anomaly (pancreas divisum) described in the imaging.
*Rotation of the midgut*
- The **midgut rotation** is a complex embryological process involving the looping and rotation of the intestines around the superior mesenteric artery.
- Errors in this process can lead to malrotation, volvulus, or intestinal atresia, but not pancreatic ductal anomalies.
Abdominal wall development US Medical PG Question 2: During a surgical procedure to repair an abdominal aortic aneurysm, the surgeon must be careful to avoid injury to which of the following arterial structures that originates near the level of the renal vessels?
- A. Left renal artery (Correct Answer)
- B. Celiac trunk
- C. Right renal artery
- D. Superior mesenteric artery
Abdominal wall development Explanation: ***Left renal artery***
- The **left renal artery** arises from the aorta usually just below the superior mesenteric artery, making it susceptible to injury during an **abdominal aortic aneurysm (AAA) repair** if the aneurysm extends proximally.
- Its proximity to the typical location of AAA, often near or involving the **infrarenal aorta**, necessitates careful identification and protection during clamping or graft placement.
*Celiac trunk*
- The **celiac trunk** originates higher up from the aorta, typically at the level of **T12-L1 vertebrae**, well above the common infrarenal AAA repair site.
- While important, it is generally less directly threatened during a typical infrarenal AAA repair compared to arteries immediately adjacent to or within the aneurysm sac.
*Right renal artery*
- The **right renal artery** also originates from the aorta near the level of the renal veins, but it is typically located more posteriorly and usually passes behind the inferior vena cava.
- Although it can be at risk, the left renal artery's course is often more anterior and directly in the field of dissection for the **aortic neck** during AAA repair.
*Superior mesenteric artery*
- The **superior mesenteric artery (SMA)** originates from the aorta proximal to the renal arteries, typically around the L1 vertebral level.
- While crucial, its origin is usually cephalad to the infrarenal aneurysm neck, making it generally less prone to direct injury during infrarenal AAA repair, though flow must be monitored.
Abdominal wall development US Medical PG Question 3: A 52-year-old woman sees you in your office with a complaint of new-onset headaches over the past few weeks. On exam, you find a 2 x 2 cm dark, irregularly shaped, pigmented lesion on her back. She is concerned because her father recently passed away from skin cancer. What tissue type most directly gives rise to the lesion this patient is experiencing?
- A. Neural crest cells (Correct Answer)
- B. Endoderm
- C. Mesoderm
- D. Ectoderm
- E. Neuroectoderm
Abdominal wall development Explanation: ***Neural crest cells***
- The suspected lesion, given its description and the patient's family history of skin cancer, is likely a **melanoma**.
- Melanoma originates from **melanocytes**, which are derived from **neural crest cells** during embryonic development.
*Endoderm*
- The endoderm gives rise to the **lining of the gastrointestinal and respiratory tracts**, as well as organs such as the liver and pancreas.
- It is not involved in the formation of melanocytes or skin lesions like melanoma.
*Mesoderm*
- The mesoderm forms tissues such as **muscle, bone, cartilage, connective tissue**, and the circulatory system.
- It does not directly give rise to melanocytes, which are the cells of origin for melanoma.
*Ectoderm*
- The ectoderm gives rise to the **epidermis, nervous system**, and sensory organs.
- While melanocytes are found in the epidermis, they are specifically derived from the **neural crest (a sub-population of ectoderm)**, not the general ectoderm.
*Neuroectoderm*
- Neuroectoderm specifically refers to the ectoderm that develops into the **nervous system**.
- While neural crest cells originate from the neuroectoderm, "neural crest cells" is a more precise answer for the origin of melanocytes.
Abdominal wall development US Medical PG Question 4: A child is in the nursery one day after birth. A nurse notices a urine-like discharge being expressed through the umbilical stump. What two structures in the embryo are connected by the structure that failed to obliterate during the embryologic development of this child?
- A. Kidney - large bowel
- B. Liver - umbilical vein
- C. Bladder - small bowel
- D. Pulmonary artery - aorta
- E. Bladder - umbilicus (Correct Answer)
Abdominal wall development Explanation: ***Bladder - umbilicus***
- A **urine-like discharge** from the umbilical stump indicates a **patent urachus**, which is the embryonic remnant of the allantois.
- The **allantois** (which becomes the urachus) is an embryonic structure that connects the **fetal bladder** to the **umbilicus** during development.
- Normally, the allantois obliterates after birth to form the **median umbilical ligament**, but failure to obliterate results in a patent urachus allowing urine to discharge through the umbilicus.
*Kidney - large bowel*
- These two structures are not directly connected by an obliterating embryonic structure relevant to urine discharge from an umbilical stump.
- The kidneys form urine, and the large bowel is part of the digestive tract, with no direct embryonic communication to the umbilicus for urine expression.
*Liver - umbilical vein*
- The umbilical vein connects the **placenta to the fetal liver** (and ductus venosus) to transport oxygenated blood, not urine.
- Failure of the umbilical vein to obliterate would result in a patent umbilical vein, typically presenting as a vascular anomaly, not urine discharge.
*Pulmonary artery - aorta*
- These structures are connected by the **ductus arteriosus** in fetal circulation, bypassing the pulmonary circulation.
- While important for fetal development, a patent ductus arteriosus (PDA) is a cardiovascular anomaly and would not manifest as urine discharge from the umbilical stump.
*Bladder - small bowel*
- While both structures are involved in waste elimination, there is no normal embryonic structure directly connecting the bladder and small bowel that obliterates to prevent urine discharge from the umbilicus.
- An abnormal connection between the bladder and bowel would typically involve a **fistula** and present with stool in urine or urine in stool, not umbilical discharge.
Abdominal wall development US Medical PG Question 5: A 23-year-old woman, gravida 2, para 1, at 26 weeks gestation comes to the physician for a routine prenatal visit. Physical examination shows a uterus consistent in size with a 26-week gestation. Fetal ultrasonography shows a male fetus with a thick band constricting the right lower arm; the limb distal to the constrictive band cannot be visualized. The most likely condition is an example of which of the following embryological abnormalities?
- A. Agenesis
- B. Disruption (Correct Answer)
- C. Aplasia
- D. Deformation
- E. Malformation
Abdominal wall development Explanation: ***Disruption***
- A **disruption** is a morphological defect of an organ or a larger body region resulting from an **extrinsic breakdown** of a previously normal developmental process.
- The **amniotic band syndrome**, causing the constricting band and absent distal limb, is a classic example of disruption due to **amniotic bands** entrapping fetal parts.
*Agenesis*
- **Agenesis** refers to the complete **absence of an organ** due to the absence of the primordial tissue from which it develops.
- In this case, the limb was initially present but was subsequently damaged, which is not agenesis.
*Aplasia*
- **Aplasia** refers to the complete **absence of an organ** when the primordial tissue was present but failed to develop.
- This differs from the scenario where a previously normally developing structure is destroyed by an extrinsic factor (disruption).
*Deformation*
- A **deformation** is an abnormality in form or position of a body part caused by **mechanical forces**, usually occurring in later fetal stages.
- Examples include clubfoot due to intrauterine compression, but it does not involve the intrinsic destruction of tissue observed here.
*Malformation*
- A **malformation** is a **primary defect** in the development of an organ or tissue due to an intrinsic abnormal developmental process.
- Examples include **cleft lip** or congenital heart defects; it is not due to an external disruptive force.
Abdominal wall development US Medical PG Question 6: A 4700-g (10.3-lb) male newborn is delivered at 37 weeks' gestation to a 30-year-old woman, gravida 2, para 1. Apgar scores are 7 and 8 at 1 and 5 minutes, respectively. The newborn appears pale. Temperature is 37°C (98.6°F), pulse is 180/min, and blood pressure is 90/60 mm Hg. Examination in the delivery room shows midfacial hypoplasia, infraorbital creases, and a large tongue. The right side of the body is larger than the left. Abdominal examination shows that the abdominal viscera protrudes through the abdominal wall at the umbilicus; the viscera are covered by the amniotic membrane and the peritoneum. The liver is palpated 2–3 cm below the right costal margin. Fingerstick blood glucose concentration is 60 mg/dL. Ultrasonography of the abdomen shows enlarged kidneys bilaterally. In addition to surgical closure of the abdominal wall, which of the following is the most appropriate next step in management?
- A. Serum 17-hydroxyprogesterone measurement
- B. Serum TSH measurement
- C. Serum IGF-1 measurement
- D. Cranial MRI
- E. Serial abdominal ultrasonography (Correct Answer)
Abdominal wall development Explanation: ***Serial abdominal ultrasonography***
- The combination of **macrosomia**, **omphalocele**, **hemihyperplasia**, **visceromegaly** (large kidneys and liver), **macroglossia** (large tongue), and **facial anomalies** is highly suggestive of **Beckwith-Wiedemann Syndrome (BWS)**.
- Children with BWS have an increased risk of developing specific **embryonal tumors**, including **Wilms tumor** and **hepatoblastoma**, making regular abdominal ultrasonography crucial for early detection.
- **Current guidelines recommend abdominal ultrasound every 3 months until age 8** for tumor surveillance.
- Note: The mild hypoglycemia (60 mg/dL) should be monitored, as neonatal hypoglycemia is common in BWS, but tumor surveillance is the critical long-term management priority.
*Serum 17-hydroxyprogesterone measurement*
- This test is used to screen for **congenital adrenal hyperplasia (CAH)**.
- The clinical presentation does not suggest CAH, as there are no signs of **ambiguous genitalia** or **salt-wasting crisis**.
*Serum TSH measurement*
- **Thyroid-stimulating hormone (TSH)** is measured to screen for **congenital hypothyroidism**.
- While lethargy and feeding difficulties can occur in hypothyroidism, the described constellation of anomalies, especially macrosomia and omphalocele, is not characteristic of this condition.
*Serum IGF-1 measurement*
- **Insulin-like growth factor 1 (IGF-1)** levels are primarily evaluated in cases of suspected **growth hormone deficiency** or **excess (gigantism/acromegaly)**.
- While BWS involves overgrowth, the initial diagnostic and screening approach for associated tumor risk does not involve IGF-1 measurement.
*Cranial MRI*
- **Cranial MRI** is indicated for neurological symptoms or suspected brain anomalies.
- The patient's presentation does not include any neurological deficits or signs suggesting intracranial pathology as the primary concern.
Abdominal wall development US Medical PG Question 7: During development, a fetus is found to have incomplete fusion of the neural tube. Which of the following structures would most likely be affected by this developmental defect?
- A. Notochord
- B. Somites
- C. Vertebral bodies
- D. Spinal cord and meninges (Correct Answer)
Abdominal wall development Explanation: ***Spinal cord and meninges***
- Incomplete fusion of the neural tube directly results in defects of the **neural tube closure**, which include the formation of the **spinal cord** and its protective coverings, the **meninges**. [1, 2]
- Conditions like **spina bifida** (meningocele, myelomeningocele) are direct consequences of these fusion failures, exposing or abnormally developing the spinal cord and meninges. [1, 2]
*Notochord*
- The **notochord** is a transient embryonic structure that induces the formation of the neural tube by signaling to the overlying ectoderm; it is not directly formed by the neural tube itself.
- While it plays a critical role in neural tube development, its own structural integrity is typically not primarily affected by neural tube fusion defects.
*Somites*
- **Somites** are blocks of paraxial mesoderm that differentiate into sclerotome (vertebrae and ribs), myotome (skeletal muscle), and dermatome (dermis of the skin).
- While somite development is closely coordinated with neural tube formation, incomplete neural tube fusion primarily affects the neural structures themselves, not the somites directly.
*Vertebral bodies*
- **Vertebral bodies** develop from the sclerotome portion of the somites, which migrate to surround the neural tube and notochord.
- While vertebral defects can be associated with severe neural tube defects (e.g., in spina bifida, the vertebral arches may fail to close), the primary defect of incomplete neural tube fusion directly impacts the neural tissue (spinal cord and meninges), with skeletal defects being secondary or associated. [1, 2]
Abdominal wall development US Medical PG Question 8: A newborn boy born vaginally to a healthy 37-year-old G3P1 from a pregnancy complicated by hydramnios fails to pass meconium after 24 hours of life. The vital signs are within normal limits for his age. The abdomen is distended, the anus is patent, and the rectal examination reveals pale mucous with non-pigmented meconium. Based on a barium enema, the boy is diagnosed with sigmoid colonic atresia. Disruption of which structure during fetal development could lead to this anomaly?
- A. Inferior mesenteric artery (Correct Answer)
- B. Superior mesenteric artery
- C. Vitelline duct
- D. Cloaca
- E. Celiac artery
Abdominal wall development Explanation: ***Inferior mesenteric artery***
- **Sigmoid colonic atresia**, as observed in this case, results from an ischemic event affecting the segment of the bowel supplied by the **inferior mesenteric artery** during fetal development.
- Interruption of blood flow to this region can lead to subsequent **atresia** as the affected part of the intestine necroses and is reabsorbed.
*Superior mesenteric artery*
- The **superior mesenteric artery** primarily supplies the midgut structures, including the small intestine and parts of the large intestine up to the transverse colon.
- Disruption of the superior mesenteric artery would typically lead to atresias higher up in the **gastrointestinal tract**, such as jejunal or ileal atresias, not sigmoid colonic atresia.
*Vitelline duct*
- The **vitelline duct** (also known as the omphalomesenteric duct) connects the midgut to the yolk sac during early fetal development.
- Persistent patency or partial obliteration of the vitelline duct can lead to anomalies like **Meckel's diverticulum** or vitelline cysts, which are distinct from colonic atresia.
*Cloaca*
- The **cloaca** is a common cavity for the digestive, urinary, and reproductive tracts during early embryonic development.
- Defects in cloacal development lead to complex malformations involving these systems, such as **imperforate anus** or persistent cloaca, rather than isolated colonic atresia with a patent anus.
*Celiac artery*
- The **celiac artery** supplies the foregut structures, including the stomach, duodenum, liver, and spleen.
- Disruption of the celiac artery during fetal development would result in malformations of these upper gastrointestinal organs, not the sigmoid colon.
Abdominal wall development US Medical PG Question 9: A male newborn is born at 37 weeks' gestation after spontaneous vaginal delivery. The mother had no prenatal care. Physical examination shows a urethral opening on the dorsal aspect of the penis, 4 mm proximal to the glans. There is a 3-cm defect in the midline abdominal wall superior to the pubic symphysis with exposure of moist, erythematous mucosa. Which of the following is the most likely underlying cause of this patient's findings?
- A. Abnormal development of the gubernaculum
- B. Persistence of the urogenital membrane
- C. Failed fusion of the urethral folds
- D. Incomplete union of the labioscrotal swellings
- E. Malpositioning of the genital tubercle (Correct Answer)
Abdominal wall development Explanation: ***Malpositioning of the genital tubercle***
- This condition describes **epispadias** (urethral opening on the dorsal aspect) and **bladder exstrophy** (abdominal wall defect with exposed bladder mucosa), which are frequently co-occurring and caused by a **ventral displacement of the genital tubercle**.
- A defect in the **abdominal wall closure** allows the bladder to remain exposed, and the abnormal positioning of the genital tubercle leads to an improperly formed urethra.
*Abnormal development of the gubernaculum*
- The gubernaculum is crucial for **testicular descent**; abnormal development would typically lead to **cryptorchidism** (undescended testes).
- It does not explain the urethral opening on the dorsal penis or the abdominal wall defect.
*Persistence of the urogenital membrane*
- Persistent urogenital membrane typically results in conditions like an **imperforate hymen** in females or **urogenital sinus anomalies**, but not epispadias or bladder exstrophy.
- This membrane normally ruptures, creating the definitive openings for the urethra and vagina.
*Failed fusion of the urethral folds*
- Failed fusion of the urethral folds in males can lead to **hypospadias**, where the urethral opening is on the **ventral** aspect of the penis.
- It does not account for the **dorsal urethral opening (epispadias)** described or the associated bladder exstrophy.
*Incomplete union of the labioscrotal swellings*
- Incomplete union of the labioscrotal swellings in males results in **bifid scrotum** or **hypospadias**.
- This doesn't explain the characteristic dorsal urethral defect of epispadias or the large abdominal wall defect associated with bladder exstrophy.
Abdominal wall development US Medical PG Question 10: A 26-year-old woman comes to the physician because she has not had a menstrual period for 5 weeks. Menarche was at the age of 14 years and menses occurred at regular 30-day intervals. She reports having unprotected sexual intercourse 3 weeks ago. A urine pregnancy test is positive. Which of the following best describes the stage of development of the embryo at this time?
- A. Fetal heart is beating, but cardiac activity is not yet visible on ultrasound
- B. Limb buds have formed, but fetal movements have not begun
- C. Sexual differentiation has begun, but fetal movement has not started
- D. Neural crest has formed, but limb buds have not yet formed (Correct Answer)
- E. Implantation has occurred, but notochord has not yet formed
Abdominal wall development Explanation: ***Neural crest has formed, but limb buds have not yet formed***
- At **5 weeks gestational age (3 weeks post-fertilization)**, neurulation is completing or recently completed
- **Neural crest cells** migrate from the neural folds during weeks 3-4 post-fertilization and are definitely present by this time
- **Limb buds** appear later, around week 4-5 post-fertilization (week 6-7 gestational age), making this the most accurate description for the current developmental stage
*Fetal heart is beating, but cardiac activity is not yet visible on ultrasound*
- The primitive heart tube begins contracting around day 22-23 post-fertilization (early week 4)
- At 3 weeks post-fertilization (5 weeks gestational age), the heart may just be starting to beat, but this timing is less precise
- Cardiac activity becomes visible on transvaginal ultrasound around 5.5-6 weeks gestational age, so this option is close but less precise than the correct answer
*Limb buds have formed, but fetal movements have not begun*
- **Limb buds** typically appear around week 4-5 post-fertilization (week 6-7 gestational age)
- This is **too advanced** for 3 weeks post-fertilization
- While fetal movements aren't perceptible to the mother until 16-20 weeks, they begin much later than the current stage
*Sexual differentiation has begun, but fetal movement has not started*
- **Sexual differentiation** of the gonads begins around week 7 post-fertilization (week 9 gestational age)
- External genitalia differentiation occurs even later (weeks 9-12 post-fertilization)
- This stage is **far too advanced** for the current 3-week post-fertilization timeframe
*Implantation has occurred, but notochord has not yet formed*
- **Implantation** occurs 6-12 days after fertilization, which is approximately 2-3 weeks before a positive pregnancy test
- The **notochord** forms during gastrulation in the **3rd week post-fertilization** (5th week gestational age)
- By the time of this positive pregnancy test (5 weeks gestational age), the notochord has **already formed**, making this statement incorrect
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