Midgut development and rotation US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Midgut development and rotation. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Midgut development and rotation US Medical PG Question 1: A 14-month-old boy has iron-deficiency anemia refractory to iron therapy. His stool is repeatedly positive for occult blood. The parents bring the child to the emergency room after they notice some blood in his stool. Which of the following is the diagnostic gold standard for this patient's most likely condition?
- A. Colonoscopy
- B. Technetium-99m pertechnetate scan (Correct Answer)
- C. Capsule endoscopy
- D. Abdominal CT with contrast
- E. Tagged red blood cell study
Midgut development and rotation Explanation: ***Technetium-99m pertechnetate scan***
- The clinical picture of **iron-deficiency anemia refractory to iron therapy**, **occult blood in the stool**, and visible blood in a 14-month-old strongly suggests a **Meckel's diverticulum** that contains ectopic gastric mucosa.
- This scan specifically detects **ectopic gastric mucosa**, which is the most common cause of bleeding from a Meckel's diverticulum, making it the **diagnostic gold standard**.
*Colonoscopy*
- While useful for evaluating the colon and rectum, **colonoscopy** is unlikely to identify a Meckel's diverticulum, which is located in the **small intestine**.
- It's primarily used for conditions like colonic polyps, inflammatory bowel disease, or lower gastrointestinal bleeding from the large bowel.
*Capsule endoscopy*
- **Capsule endoscopy** can visualize the small bowel mucosa and detect bleeding, but it does not specifically identify **ectopic gastric mucosa** and may miss a Meckel's diverticulum, especially if it's not actively bleeding at the time of the study.
- It is also less commonly used in very young children due to issues with capsule passage and retention.
*Abdominal CT with contrast*
- An **abdominal CT with contrast** can identify some structural abnormalities and inflammation but is generally not the primary diagnostic tool for a Meckel's diverticulum.
- It has **limited sensitivity** for detecting ectopic gastric mucosa or the diverticulum itself, particularly if it's small or not inflamed.
*Tagged red blood cell study*
- A **tagged red blood cell study** can detect the site of active gastrointestinal bleeding, but it does not identify the **underlying cause** of the bleeding, such as a Meckel's diverticulum.
- It requires active bleeding at a rate of at least 0.1 mL/min to be positive, and may be less specific than a Meckel's scan for this particular pathology.
Midgut development and rotation 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
Midgut development and rotation 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.
Midgut development and rotation US Medical PG Question 3: A 2-year-old male is brought to his pediatrician by his mother because of abdominal pain and blood in the stool. Scintigraphy reveals uptake in the right lower quadrant of the abdomen. Persistence of which of the following structures is the most likely cause of this patient's symptoms?
- A. Ureteric bud
- B. Urachus
- C. Paramesonephric duct
- D. Omphalomesenteric duct (Correct Answer)
- E. Allantois
Midgut development and rotation Explanation: ***Omphalomesenteric duct***
- Persistence of the **omphalomesenteric duct** (vitelline duct) can lead to a **Meckel's diverticulum**, which often contains **ectopic gastric or pancreatic tissue**.
- This ectopic tissue can cause **ulceration and bleeding**, leading to abdominal pain and **melena** (blood in stool), and will show uptake on a Technetium-99m pertechnetate scan (scintigraphy) for ectopic gastric mucosa.
*Ureteric bud*
- The ureteric bud forms the **ureter, renal pelvis, calyces**, and **collecting ducts** of the kidney.
- Anomalies of the ureteric bud typically present with **urinary tract issues**, such as hydronephrosis or renal agenesis, not abdominal pain and bloody stools from GI bleeding.
*Urachus*
- The urachus is a remnant of the **allantois** connecting the fetal bladder to the umbilicus.
- Persistent urachal remnants can cause urine leakage from the umbilicus, cysts, or infections, but generally not abdominal pain and bloody stools.
*Paramesonephric duct*
- The paramesonephric (Müllerian) ducts form the **female reproductive organs** (fallopian tubes, uterus, cervix, upper vagina).
- Persistence or anomalies of these ducts are relevant to **gynecological issues** and infertility in females, not the GI symptoms described in a male child.
*Allantois*
- The allantois contributes to the formation of the **urachus** and is involved in early blood formation and bladder development.
- While related to the urachus, its direct persistence or anomalies typically don't cause the specific presentation of abdominal pain and bloody stools due to ectopic gastric mucosa.
Midgut development and rotation US Medical PG Question 4: A mother brings her 1-week-old son to the pediatrician because she is concerned about the child’s umbilicus. She notes that there appears to be fluid draining from the child’s umbilicus several times a day. The child has been breastfeeding normally. On exam, a small amount of clear light yellow fluid drains from the child’s umbilical stump when pressure is applied to the child’s lower abdomen. No bilious or feculent drainage is noted. Which of the following embryologic structures is associated with this patient’s condition?
- A. Paramesonephric duct
- B. Urachus (Correct Answer)
- C. Umbilical vein
- D. Ductus venosus
- E. Omphalomesenteric duct
Midgut development and rotation Explanation: ***Urachus***
- The draining of clear, light yellow fluid from the umbilical stump on abdominal pressure is characteristic of a **patent urachus**, which is a remnant of the **allantois**.
- A patent urachus connects the **umbilical cord** to the **bladder**, allowing urine to leak through the umbilicus.
*Paramesonephric duct*
- The paramesonephric (Müllerian) duct develops into female reproductive structures like the **fallopian tubes**, **uterus**, and **upper vagina**.
- It is not associated with umbilical drainage or the urinary system.
*Umbilical vein*
- The umbilical vein carries **oxygenated blood** from the placenta to the fetus and typically obliterates to form the **ligamentum teres hepatis**.
- Its patency would lead to vascular issues, not fluid drainage from the umbilicus.
*Ductus venosus*
- The ductus venosus shunts **oxygenated blood** from the umbilical vein directly to the inferior vena cava, bypassing the liver.
- It obliterates to form the **ligamentum venosum** and is not involved in umbilical fluid leakage.
*Omphalomesenteric duct*
- The omphalomesenteric (vitelline) duct connects the **fetal midgut** to the **yolk sac** during early development.
- A patent omphalomesenteric duct would typically present with **feculent** or **bilious drainage** from the umbilicus, not clear, light yellow fluid, as it is connected to the digestive tract.
Midgut development and rotation US Medical PG Question 5: A 5-year-old girl is brought to a medical office for evaluation of persistent abdominal pain that has worsened over the past 24 hours. The mother states that the girl often has constipation which has worsened over the last 3 days. The mother denies that the girl has had bloody stools. The girl has not had a bowel movement or passed flatulence in 72 hours. She has vomited 3 times since last night and refuses to eat. She has no significant medical history, including no history of surgeries. On exam, there are no abdominal masses; however, the upper abdomen is distended and tympanic. What is the most likely underlying cause of the girl’s symptoms?
- A. Duodenal atresia
- B. Malrotation of the gut (Correct Answer)
- C. Pyloric stenosis
- D. Meckel’s diverticulum
- E. Volvulus
Midgut development and rotation Explanation: ***Malrotation of the gut***
- The question asks for the **underlying cause** of symptoms in a 5-year-old presenting with her **first episode** of acute bowel obstruction and **no prior surgical history**. **Malrotation** is the congenital anatomical abnormality that predisposes to **midgut volvulus**.
- **Malrotation** occurs when the bowel fails to rotate properly during fetal development, leaving the mesentery on a narrow pedicle. This anatomical defect is the underlying cause that makes volvulus possible.
- While volvulus (twisting) is the acute mechanical event causing obstruction, **malrotation is the underlying anatomical defect** being asked for in the question.
- The presentation of **abdominal pain**, **vomiting**, **abdominal distension**, inability to pass **flatus or stool** for 72 hours, and **tympanic upper abdomen** indicates acute bowel obstruction from midgut volvulus occurring on the background of malrotation.
*Volvulus*
- **Volvulus** (twisting of the bowel) is the **acute complication** that occurs, not the underlying cause.
- Volvulus is the mechanism of obstruction, but it occurs because of the underlying anatomical defect (malrotation).
- The question specifically asks for "underlying cause" - volvulus is the acute event, while malrotation is the predisposing anatomical abnormality.
*Duodenal atresia*
- **Duodenal atresia** is a congenital complete obstruction that presents in the **neonatal period** with vomiting (bilious), the classic "double bubble" sign, and feeding intolerance.
- This would have been diagnosed much earlier than 5 years of age and is not compatible with this presentation.
*Pyloric stenosis*
- **Pyloric stenosis** presents with **non-bilious projectile vomiting** in infants between **2 to 6 weeks of age**, not in a 5-year-old child.
- Physical exam classically reveals an **olive-shaped mass** in the epigastrium and visible gastric peristaltic waves.
*Meckel's diverticulum*
- **Meckel's diverticulum** most commonly presents with **painless rectal bleeding** (from ectopic gastric mucosa causing ulceration) following the "rule of 2s."
- While it can cause obstruction via intussusception or serve as a lead point, it is not the most likely underlying cause of this presentation in a 5-year-old with acute complete bowel obstruction and no prior symptoms.
Midgut development and rotation US Medical PG Question 6: An 18-month-old boy is brought to the physician by his parents for the evaluation of passing large amounts of dark red blood from his rectum for 2 days. His parents noticed that he has also had several episodes of dark stools over the past 3 weeks. The parents report that their child has been sleeping more and has been more pale than usual over the past 24 hours. The boy's appetite has been normal and he has not vomited. He is at the 50th percentile for height and 50th percentile for weight. His temperature is 37°C (98.6°F), pulse is 135/min, respirations are 38/min, and blood pressure is 90/50 mm Hg. Examination shows pale conjunctivae. The abdomen is soft and nontender. There is a small amount of dark red blood in the diaper. Laboratory studies show:
Hemoglobin 9.5 g/dL
Hematocrit 30%
Mean corpuscular volume 68 μm3
Leukocyte count 7,200/mm3
Platelet count 300,000/mm3
Which of the following is most likely to confirm the diagnosis?
- A. Colonoscopy
- B. Water-soluble contrast enema
- C. Technetium-99m pertechnetate scan (Correct Answer)
- D. Esophagogastroduodenoscopy
- E. Plain abdominal x-ray
Midgut development and rotation Explanation: **Technetium-99m pertechnetate scan**
- The presentation of painless **dark red rectal bleeding** in a toddler, coupled with signs of **anemia** (pale conjunctivae, hemoglobin 9.5 g/dL, MCV 68 μm³), strongly suggests a **Meckel's diverticulum** with ectopic gastric mucosa.
- A **Technetium-99m pertechnetate scan** specifically detects **ectopic gastric mucosa**, which is the most common cause of bleeding in a Meckel's diverticulum, making it the definitive diagnostic test.
*Colonoscopy*
- While useful for evaluating lower gastrointestinal bleeding, a **colonoscopy** is less likely to detect a Meckel's diverticulum, which often lies beyond the reach of a standard colonoscope.
- It involves more invasive preparation and carries higher risks for a young child compared to a nuclear scan for this specific suspicion.
*Water-soluble contrast enema*
- A **water-soluble contrast enema** is primarily used to diagnose conditions like intussusception or colonic obstructions by visualizing the bowel lumen.
- It is unlikely to visualize a Meckel's diverticulum or identify the bleeding source directly, especially one involving ectopic gastric mucosa.
*Esophagogastroduodenoscopy*
- An **esophagogastroduodenoscopy (EGD)** evaluates the upper gastrointestinal tract (esophagus, stomach, duodenum).
- The symptom of **dark red rectal bleeding** indicates a lower GI source, making an EGD a less appropriate initial diagnostic step.
*Plain abdominal x-ray*
- A **plain abdominal x-ray** is useful for identifying bowel obstruction, perforation, or foreign bodies, but it does not directly visualize or diagnose causes of GI bleeding like a Meckel's diverticulum.
- It provides limited information regarding the source of internal bleeding or the presence of anomalous tissue.
Midgut development and rotation US Medical PG Question 7: An 8-month-old boy is brought to a medical office by his mother. The mother states that the boy has been very fussy and has not been feeding recently. The mother thinks the baby has been gaining weight despite not feeding well. The boy was delivered vaginally at 39 weeks gestation without complications. On physical examination, the boy is noted to be crying in his mother’s arms. There is no evidence of cyanosis, and the cardiac examination is within normal limits. The crying intensifies when the abdomen is palpated. The abdomen is distended with tympany in the left lower quadrant. You suspect a condition caused by the failure of specialized cells to migrate. What is the most likely diagnosis?
- A. Duodenal atresia
- B. Hirschsprung disease (Correct Answer)
- C. Meckel diverticulum
- D. Pyloric stenosis
- E. DiGeorge syndrome
Midgut development and rotation Explanation: ***Correct: Hirschsprung disease***
- This diagnosis is characterized by the **failure of neural crest cells** to migrate, leading to an **aganglionic segment of the colon** that cannot relax.
- Symptoms like **abdominal distension**, **vomiting**, and **failure to thrive** in an 8-month-old are consistent with Hirschsprung disease.
*Incorrect: Duodenal atresia*
- **Duodenal atresia** typically presents in the **neonatal period** with **bilious vomiting** and a **double-bubble sign** on imaging.
- It is a congenital obstruction but does not involve the failed migration of specialized cells, and distension with tympany in the lower quadrant is not a primary feature.
*Incorrect: Meckel diverticulum*
- A **Meckel diverticulum** is a remnant of the **vitelline duct** and is often asymptomatic or can cause **painless rectal bleeding**.
- It does not present with the described symptoms of abdominal distention and fussiness related to an intestinal obstruction or motility disorder caused by cellular migration failure.
*Incorrect: Pyloric stenosis*
- **Pyloric stenosis** typically presents with **projectile non-bilious vomiting** and an **olive-shaped mass** in the epigastrium, usually between 2 and 8 weeks of age.
- The symptoms described, such as marked abdominal distention and crying intensifying with abdominal palpation, are not typical for pyloric stenosis.
*Incorrect: DiGeorge syndrome*
- **DiGeorge syndrome** is a genetic disorder associated with **thymic and parathyroid hypoplasia**, leading to **T-cell immunodeficiency** and **hypocalcemia**.
- While it involves developmental anomalies, it does not directly present with gastrointestinal obstruction or motility issues caused by failed cell migration as the primary symptom.
Midgut development and rotation 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
Midgut development and rotation 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.
Midgut development and rotation US Medical PG Question 9: A 60-year-old gentleman passes away after a car accident. On routine autopsy it is incidentally noted that he has both a ventral and dorsal pancreatic duct. This incidental finding observed by the pathologist is generated due to failure of which of the following embryological processes?
- A. Apoptosis
- B. Stem cell differentiation
- C. Notochord signaling
- D. Neural crest cell migration
- E. Fusion (Correct Answer)
Midgut development and rotation Explanation: ***Fusion***
- The pancreas develops from a **ventral and a dorsal bud** that typically **fuse** during development.
- Failure of these two pancreatic buds (and their associated ducts) to completely fuse can result in **pancreas divisum**, where two separate ductal systems persist, corresponding to the dorsal and ventral pancreatic ducts.
*Apoptosis*
- **Apoptosis** (programmed cell death) is crucial for the removal of unwanted cells and sculpting tissues during embryogenesis, such as the formation of digits or the regression of certain structures.
- It does not directly explain the persistence of two separate pancreatic ducts due to non-fusion of developmental buds.
*Stem cell differentiation*
- **Stem cell differentiation** is the process by which less specialized stem cells become more specialized cell types, which is fundamental to organ development and tissue formation.
- While essential for pancreatic development, it doesn't specifically account for the anatomical anomaly of two persistent ducts.
*Notochord signaling*
- **Notochord signaling** is vital for inducing the formation of the neural tube and defining the dorsal-ventral axis of the embryo, as well as influencing the development of other nearby structures.
- This process is not directly related to the fusion of pancreatic buds, which occurs later and is influenced by interactions between mesenchymal and endodermal tissues.
*Neural crest cell migration*
- **Neural crest cells** are multipotent cells that migrate extensively throughout the embryo to form a wide variety of tissues, including parts of the peripheral nervous system, melanocytes, and bone/cartilage of the face and skull.
- Their migratory pathways and derivatives are not directly involved in the development and fusion of the pancreatic ductal system.
Midgut development and rotation US Medical PG Question 10: A 4-year-old girl is brought to the physician because her mother is concerned that she has been talking to an imaginary friend for 2 months. The child calls her friend 'Lucy' and says “Lucy is my best friend”. The child has multiple conversation and plays with the 'Lucy' throughout the day. The girl attends preschool regularly. She can copy a circle, tells stories, and can hop on one foot. Her maternal uncle has schizophrenia. Her parents are currently divorcing. The child's father has a history of illicit drug use. Physical examination shows no abnormalities. The mother is concerned about whether the child is acting out because of the divorce. Which of the following is the most appropriate next best step in management?
- A. Reassure the mother (Correct Answer)
- B. Perform MRI of the brain
- C. Schedule psychiatry consult
- D. Inform Child Protective Services
- E. Screen urine for drugs
Midgut development and rotation Explanation: ***Reassure the mother***
- Imaginary friends are a **normal developmental phenomenon** in preschool-aged children, often associated with creativity and good social skills.
- The child's developmental milestones (copying a circle, hopping, telling stories) are appropriate for her age, indicating **healthy cognitive and motor development**.
*Perform MRI of the brain*
- There are **no neurological symptoms** or concerning signs in this case that would warrant an MRI of the brain.
- Imaginary friends are not indicative of a brain abnormality or neurological disorder.
*Schedule psychiatry consult*
- A psychiatry consult is **not indicated** as the child's behavior is developmentally appropriate.
- While there is a family history of schizophrenia and parental stress, the child is exhibiting typical childhood play and not symptoms of a mental health disorder.
*Inform Child Protective Services*
- There is **no evidence of child abuse or neglect** in the provided information.
- Although the parents are divorcing and the father has a history of drug use, there are no specific concerns raised about the child's safety or well-being that would require CPS involvement.
*Screen urine for drugs*
- A drug screen is **not relevant** to the child's behavior or a concern for drug use by the child.
- While the father has a history of illicit drug use, this does not automatically imply the child is being exposed to drugs, and the child's symptoms are unrelated to drug exposure.
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