Hindgut development US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Hindgut development. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Hindgut development US Medical PG Question 1: 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
Hindgut 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.
Hindgut development US Medical PG Question 2: A 2-year-old boy is brought in to his pediatrician for a routine checkup. The parents mention that the child has been developing appropriately, although they have been noticing that the child appears to have chronic constipation. The parents report that their child does not routinely have daily bowel movements, and they have noticed that his abdomen has become more distended recently. In the past, they report that the patient was also delayed in passing meconium, but this was not further worked up. On exam, his temperature is 98.6°F (37.0°C), blood pressure is 110/68 mmHg, pulse is 74/min, and respirations are 14/min. The patient is noted to have a slightly distended abdomen that is nontender. Eventually, this patient undergoes a biopsy. Which of the following layers most likely reveals the causative pathologic finding of this disease?
- A. Submucosa
- B. Mucosa
- C. Lamina propria
- D. Muscularis mucosa
- E. Muscularis propria (between muscle layers) (Correct Answer)
Hindgut development Explanation: ***Muscularis propria (between muscle layers)***
- This patient's presentation with **chronic constipation**, **abdominal distention**, and **delayed meconium passage** is highly suggestive of **Hirschsprung disease**.
- The causative pathology in Hirschsprung disease is the **absence of ganglion cells** in the **myenteric (Auerbach's) and submucosal (Meissner's) plexuses**, which is definitively diagnosed by a rectal biopsy showing this lack of innervation.
- The **myenteric plexus** is located **between the inner circular and outer longitudinal layers** of the **muscularis propria**, making this the primary layer examined for diagnostic findings.
*Submucosa*
- While the **submucosal (Meissner's) plexus** is also affected in Hirschsprung disease and the submucosa can show absent ganglion cells, the **myenteric plexus** in the muscularis propria is the primary diagnostic target in rectal biopsies.
- Both plexuses are affected, but the muscularis propria is considered the most definitive layer for diagnosis.
*Mucosa*
- The **mucosa** is the innermost layer of the gastrointestinal tract, consisting of epithelium, lamina propria, and muscularis mucosa.
- This layer does **not** contain the enteric nervous system plexuses (myenteric or submucosal) responsible for gut motility, so biopsy of this layer alone would not reveal the absent ganglion cells characteristic of Hirschsprung disease.
*Lamina propria*
- The **lamina propria** is a thin layer of connective tissue found within the **mucosa**, beneath the epithelium.
- This layer primarily contains blood vessels, lymphatics, and immune cells, and it is **not** where the ganglion cells of the enteric nervous system are located or where the primary pathology of Hirschsprung disease is found.
*Muscularis mucosa*
- The **muscularis mucosa** is a thin layer of smooth muscle that forms the outermost layer of the **mucosa**.
- It does not contain the enteric plexuses (myenteric or submucosal) responsible for gut motility, so its biopsy would not reveal the absent ganglion cells characteristic of Hirschsprung disease.
Hindgut development US Medical PG Question 3: During embryological development, failure of the urorectal septum to completely separate the cloaca results in which of the following congenital anomalies?
- A. Imperforate anus
- B. Cloacal exstrophy
- C. Rectovaginal fistula
- D. Persistent cloaca (Correct Answer)
Hindgut development Explanation: During embryological development, failure of the urorectal septum to completely separate the cloaca results in which of the following congenital anomalies?
***Persistent cloaca***
- This condition occurs when the **urorectal septum** fails to fully descend and partition the cloaca into the urogenital sinus anteriorly and the anorectal canal posteriorly [1].
- As a result, the rectum, vagina, and urinary tract all drain into a **single common channel**, leading to various functional and anatomical complications [1].
*Imperforate anus*
- This anomaly involves the **absence or abnormal closure of the anal opening**, but it does not typically involve a shared channel with the urinary or reproductive tracts.
- It arises from abnormal development of the **hindgut's caudal portion** or failure of the anal membrane to rupture.
*Cloacal exstrophy*
- This is a more complex and severe malformation characterized by the **exposure of the bladder, bowel, and sometimes genitalia** to the outside of the body.
- While it involves cloacal derivatives, it's primarily a defect in the **closure of the ventral body wall** and does not directly result from incomplete septation in the same manner as a persistent cloaca.
*Rectovaginal fistula*
- This is an **abnormal connection between the rectum and the vagina**. While it involves a communication between two distinct structures, it is a localized defect.
- It typically arises from **incomplete separation of the rectum and vagina**, which can be a consequence of less severe septation defects, but it is not the complete persistence of a single common channel like persistent cloaca.
Hindgut development US Medical PG Question 4: Two days following the home birth of her son, a mother brings the infant to the pediatric emergency room because of bilious vomiting. He is unable to pass meconium and his abdomen is distended. Endoscopic biopsy of the distal rectum demonstrates an absence of Meissner's and Auerbach's plexi in the bowel wall. Which of the following is the most likely diagnosis?
- A. Juvenile polyposis syndrome
- B. Hirschsprung’s disease (Correct Answer)
- C. Ileocecal intussusception
- D. Volvulus of the sigmoid colon
- E. Meckel’s diverticulum
Hindgut development Explanation: **Hirschsprung’s disease**
- The classic presentation includes **bilious vomiting**, **abdominal distention**, and failure to pass **meconium** in a newborn, all indicative of a distal bowel obstruction.
- The definitive diagnosis is confirmed by a rectal biopsy showing the **absence of Meissner's (submucosal) and Auerbach's (myenteric) plexi**, which are essential for normal peristalsis.
*Juvenile polyposis syndrome*
- This is a condition characterized by the development of **multiple hamartomatous polyps** in the gastrointestinal tract, primarily in the colon.
- It typically presents with **rectal bleeding** and anemia, and less commonly with obstruction; it is not associated with the absence of ganglion cells.
*Ileocecal intussusception*
- This condition involves the **telescoping of one part of the intestine into another**, often presenting with sudden onset of intermittent abdominal pain, "currant jelly" stools, and a palpable "sausage-shaped" mass.
- It generally occurs in older infants and children and would not show an **absence of Meissner's and Auerbach's plexi**.
*Volvulus of the sigmoid colon*
- Sigmoid volvulus involves the **twisting of the sigmoid colon** around its mesentery, leading to obstruction and vascular compromise.
- It is rare in newborns and more common in older adults or individuals with chronic constipation, and typically presents with a rapidly distending abdomen and severe pain, without primary neural tissue anomalies.
*Meckel’s diverticulum*
- This is a **congenital outpouching of the small intestine** resulting from incomplete obliteration of the vitelline duct.
- While it can cause obstruction, bleeding, or inflammation (mimicking appendicitis), it usually presents with painless rectal bleeding or acute abdominal pain, and does not involve the absence of ganglion cells.
Hindgut development US Medical PG Question 5: A 62-year-old female presents to her primary care physician complaining of bloody stool. She reports several episodes of bloody stools over the past two months as well as a feeling of a mass near her anus. She has one to two non-painful bowel movements per day. She has a history of alcohol abuse and hypertension. Anoscopy reveals engorged vessels. Which of the following vessels most likely drains blood from the affected region?
- A. Internal pudendal vein
- B. Left colic vein
- C. Inferior rectal vein (Correct Answer)
- D. Middle rectal vein
- E. Superior rectal vein
Hindgut development Explanation: ***Inferior rectal vein***
- The patient's symptoms (bloody stool, anal mass, engorged vessels on anoscopy) are classic for **external hemorrhoids**.
- **External hemorrhoids** are distended veins located **below the dentate line** in the anal canal, which are drained by the **inferior rectal veins**.
- The inferior rectal veins drain into the **internal pudendal vein**, then to the **internal iliac vein** (part of the **systemic venous circulation**).
*Internal pudendal vein*
- The **internal pudendal vein** drains structures in the perineum and external genitalia, but it is not the **primary/direct drainage** for hemorrhoids.
- It receives blood from the inferior rectal veins but is one step removed from the hemorrhoidal plexus itself.
*Left colic vein*
- The **left colic vein** typically drains the distal transverse colon and descending colon.
- It is part of the **inferior mesenteric venous system** and is anatomically distant from the anorectal region, not involved in draining hemorrhoids.
*Middle rectal vein*
- The **middle rectal vein** drains the middle part of the rectum and connects both portal and systemic circulations.
- It drains the **muscularis layer** of the rectum but is not the primary drainage for the external hemorrhoidal plexus below the dentate line.
*Superior rectal vein*
- The **superior rectal vein** drains the upper part of the rectum and anal canal **above the dentate line**.
- Distention of these veins leads to **internal hemorrhoids**, which are typically painless unless prolapsed or thrombosed.
- It drains into the **inferior mesenteric vein** (part of the **portal venous circulation**).
Hindgut development US Medical PG Question 6: A 2-day-old newborn boy has failed to pass meconium after 48 hours. There is an absence of stool in the rectal vault. Family history is significant for MEN2A syndrome. Which of the following confirms the diagnosis?
- A. Barium enema demonstrating absence of a transition zone
- B. Atrophic nerve fibers and increased acetylcholinesterase activity
- C. Rectal manometry demonstrating relaxation of the internal anal sphincter with distension of the rectum
- D. Genetic testing confirming mutation in the RET oncogene
- E. Absence of ganglion cells demonstrated by rectal suction biopsy (Correct Answer)
Hindgut development Explanation: ***Absence of ganglion cells demonstrated by rectal suction biopsy***
- The **absence of ganglion cells** in the colorectum, particularly on a **rectal suction biopsy**, is the definitive diagnostic feature of **Hirschsprung disease**.
- This congenital condition is characterized by the **failure of neural crest cells to migrate** to the distal bowel, leading to an aganglionic segment that cannot relax, resulting in functional obstruction.
*Barium enema demonstrating absence of a transition zone*
- A **barium enema** is a useful initial imaging study for suspected **Hirschsprung disease**, often showing a **transition zone** between a constricted aganglionic segment and a dilated, normally innervated proximal bowel.
- The *absence* of a transition zone would make **Hirschsprung disease** *less likely* or could indicate **total colonic aganglionosis**, but it is not a direct confirmatory diagnostic finding and still requires biopsy.
*Atrophic nerve fibers and increased acetylcholinesterase activity*
- While increased **acetylcholinesterase activity** in hypertrophied nerve fibers is a characteristic finding in the muscularis mucosa and submucosa of aganglionic segments in **Hirschsprung disease**, the description of "*atrophic* nerve fibers" is incorrect.
- The abnormal nerve fibers are typically hypertrophic, and this finding from specialized staining on a biopsy supports the diagnosis but is not the primary confirmatory feature itself; the **absence of ganglion cells** is paramount.
*Rectal manometry demonstrating relaxation of the internal anal sphincter with distension of the rectum*
- **Rectal manometry** is used to assess the neuromuscular function of the rectum and anal sphincter. In **Hirschsprung disease**, there is a characteristic **failure of the internal anal sphincter to relax** when the rectum is distended.
- Demonstrating normal *relaxation* of the internal anal sphincter would effectively *rule out* **Hirschsprung disease**, as the **failure of relaxation** is a key physiological abnormality.
*Genetic testing confirming mutation in the RET oncogene*
- Mutations in the **RET oncogene** are associated with **Hirschsprung disease**, especially in familial cases and those associated with syndromic forms like **MEN2A**.
- While a positive genetic test can support the diagnosis and guide genetic counseling, it is **not sufficient for a definitive diagnosis** on its own, as penetrance is variable and the definitive diagnosis relies on histological confirmation of aganglionosis.
Hindgut development US Medical PG Question 7: 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
Hindgut 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.
Hindgut development US Medical PG Question 8: 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)
Hindgut development 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.
Hindgut development US Medical PG Question 9: 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
Hindgut development 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.
Hindgut development US Medical PG Question 10: A 45-year-old male is brought to the emergency department by emergency medical services after sustaining a gunshot wound to the abdomen. He is unresponsive. His temperature is 99.0°F (37.2°C), blood pressure is 95/58 mmHg, pulse is 115/min, and respirations are 20/min. Physical examination reveals an entry wound in the left abdominal quadrant just inferior to the left lateral costal border. Abdominal CT shows the bullet trajectory through the left abdominal cavity. Which of the following structures has the bullet most likely penetrated?
- A. Transverse colon
- B. Ascending colon
- C. Descending colon (Correct Answer)
- D. Sigmoid colon
- E. Superior duodenum
Hindgut development Explanation: ***Descending colon***
- The **descending colon** is located in the left abdominal cavity, specifically in the left upper quadrant and extending into the left lower quadrant, making it highly susceptible to injury from a gunshot wound in the **left abdominal quadrant** just inferior to the left lateral costal border.
- Its position aligns directly with the described entry point and bullet trajectory.
*Transverse colon*
- The **transverse colon** lies more centrally in the upper abdomen, spanning from the right to the left upper quadrants.
- While possible to be hit by a left-sided entry wound, the trajectory described as "inferior to the left lateral costal border" makes the descending colon a more direct and likely target.
*Ascending colon*
- The **ascending colon** is located in the **right abdominal cavity**, specifically in the right upper and lower quadrants.
- A wound inferior to the left lateral costal border would be on the opposite side of the abdomen and thus unlikely to penetrate the ascending colon.
*Sigmoid colon*
- The **sigmoid colon** is located more inferiorly in the **left lower quadrant** and pelvis.
- While on the left side, the entry wound described as "inferior to the left lateral costal border" is generally higher than the typical location of the sigmoid colon.
*Superior duodenum*
- The **superior duodenum** is located in the **right upper quadrant** of the abdomen, anterior to the head of the pancreas.
- Its position on the right side makes it highly unlikely to be penetrated by a gunshot wound to the left abdominal quadrant.
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