A 2-month-old infant boy is brought into the clinic for a well-child check. Mom reports a healthy pregnancy with no complications. Though she said the ultrasound technician saw “some white deposits in his brain” during a prenatal check, mom was not concerned. The baby was delivered at 38 weeks of gestation during a home birth. When asked if there were any problems with the birthing process, mom denied any difficulties except that “he was small and had these blue dots all over.” Physical exam was unremarkable except for the absence of object tracking. What other finding would you expect?
Q82
A 4-year-old girl is being followed by the pediatric oncology team after her pediatrician found a palpable abdominal mass towards the right flank 2 weeks ago. Abdominal ultrasonography detected a solid mass in the right kidney without infiltration of the renal vein and inferior vena cava. The contrast-enhanced computed tomography (CT) confirmed the presence of a solitary mass in the right kidney surrounded by a pseudocapsule consisting of a rim of normal tissue, displacing it medially, and distorting the collecting system. No nodal involvement was detected. In which of the following chromosomes would you expect a genetic abnormality?
Q83
A 3175-g (7-lb) female newborn is delivered at term. Initial examination shows a distended abdomen and a flat perineal region without an opening. A dark green discharge is coming out of the vulva. Which of the following is the most likely diagnosis?
Q84
A 7-year-old Caucasian girl with asthma presents to her pediatrician with recurrent sinusitis. The patient’s mother states that her asthma seems to be getting worse and notes that ‘lung problems run in the family’. The patient has had 2 episodes of pneumonia in the last year and continues to frequently have a cough. Her mother says that 1 of her nieces was recently diagnosed with cystic fibrosis. On physical examination, the child has clubbing of the nail beds on both hands. A chloride sweat test is performed on the patient, and the child’s sweat chloride concentration is found to be within normal limits. The physician is still suspicious for cystic fibrosis and believes the prior asthma diagnosis is incorrect. Which of the following diagnostic tests would aid in confirming this physician’s suspicions?
Q85
A 7-year-old boy is being evaluated in pediatric cardiology clinic. He appears grossly normal, but suddenly becomes tachypneic and cyanotic when his mom takes a toy away from him. These symptoms resolve somewhat when he drops into a squatting position. Transthoracic echocardiography reveals pulmonic stenosis, a ventricular septal defect, right ventricular hypertrophy, and an overriding aorta. Which of the following best predicts the degree of cyanosis and other hypoxemic symptoms in this patient?
Q86
A 3400-g (7-lb 8-oz) female newborn is delivered at term to a 28-year-old primigravid woman. Apgar scores are 7 and 8 at 1 and 5 minutes, respectively. Vital signs are within normal limits. Examination shows swelling of bilateral upper and lower extremities and low-set ears. The posterior hair line is low and the chest appears broad. There are skin folds running down the sides of the neck to the shoulders. A grade 2/6 systolic ejection murmur and systolic click is heard at the apex. Which of the following is the most likely cause of this patient's swelling?
Q87
A 2-hours-old neonate is found to have bluish discoloration throughout his body, including lips and tongue. The boy was born at 39 weeks gestation via spontaneous vaginal delivery with no prenatal care. Maternal history is positive for type 2 diabetes mellitus for 11 years. On physical examination, his blood pressure is 55/33 mm Hg, his heart rate is 150/min, respiratory rate is 45/min, temperature of 37°C (98.6°F), and oxygen saturation is 84% on room air. Appropriate measures are taken. Auscultation of the chest reveals a single second heart sound without murmurs. Chest X-ray is shown in the exhibit. Which of the following is the most likely diagnosis?
Q88
A 2-year-old boy is brought in to the pediatrician by his mother because she is concerned that he is not gaining weight. She reports that the patient has a good appetite, eats a varied diet of solid foods, and drinks 2 cups of milk a day. The patient's mother also reports that he has foul-smelling stools over 6 times a day. The patient has a history of recurrent bronchiectasis and chronic sinusitis. On physical examination, multiple nasal polyps are appreciated and scattered rhonchi are heard over both lung fields. The patient is below the 25th percentile in height and weight. Genetic testing is ordered to confirm the suspected diagnosis. Which of the following is the most common complication associated with the patient's most likely diagnosis?
Q89
A 6-year-old boy is brought to the physician by his mother who is concerned about his early sexual development. He has no history of serious illness and takes no medications. He is at the 99th percentile for height and 70th percentile for weight. His blood pressure is 115/78 mm Hg. Examination shows greasy facial skin and cystic acne on his forehead and back. There is coarse axillary and pubic hair. Serum studies show:
Cortisol (0800 h) 4 μg/dL
Deoxycorticosterone 2.5 ng/dL (N = 3.5–11.5)
Dehydroepiandrosterone sulfate 468 mcg/dL (N = 29–412)
Which of the following is the most likely underlying cause of this patient's symptoms?
Q90
An 8-year-old girl is brought to the physician because of a progressive swelling of her neck for the past 6 months. She has no pain, dyspnea, or dysphagia. She is at the 60th percentile for height and the 55th percentile for weight. Vital signs are within normal limits. Examination shows a 3-cm cystic, nontender swelling in the midline of the neck. The swelling moves upwards on protrusion of the tongue. There is no cervical lymphadenopathy. Her serum thyroid-stimulating hormone level is 2.1 μU/mL. Which of the following is the most appropriate next step in management?
Congenital defects US Medical PG Practice Questions and MCQs
Question 81: A 2-month-old infant boy is brought into the clinic for a well-child check. Mom reports a healthy pregnancy with no complications. Though she said the ultrasound technician saw “some white deposits in his brain” during a prenatal check, mom was not concerned. The baby was delivered at 38 weeks of gestation during a home birth. When asked if there were any problems with the birthing process, mom denied any difficulties except that “he was small and had these blue dots all over.” Physical exam was unremarkable except for the absence of object tracking. What other finding would you expect?
A. Continuous machine-like murmur
B. Skin vesicles
C. Sensorineural hearing loss (Correct Answer)
D. Hutchinson teeth
E. Limb hypoplasia
Explanation: ***Sensorineural hearing loss***
- The infant's symptoms, including **intracranial calcifications** (white deposits in the brain), **small for gestational age (SGA)**, and **petechiae** (blue dots), are classic signs of congenital cytomegalovirus (CMV) infection.
- **Sensorineural hearing loss** is the most common long-term sequela of congenital CMV, affecting a significant portion of symptomatic infants, and can be progressive.
*Continuous machine-like murmur*
- A **continuous machine-like murmur** is characteristic of a **patent ductus arteriosus (PDA)**, a common finding in congenital **rubella syndrome** and prematurity, but less specific to CMV.
- While CMV can cause various congenital anomalies, PDA is not a primary or defining feature of **congenital CMV infection**.
*Skin vesicles*
- **Skin vesicles**, especially in a dermatomal pattern, are characteristic of **congenital varicella syndrome** or **herpes simplex virus (HSV)** infection.
- CMV typically presents with **petechiae** or a **blueberry muffin rash** due to extramedullary hematopoiesis, not vesicles.
*Hutchinson teeth*
- **Hutchinson teeth** are a classic sign of **congenital syphilis**, along with interstitial keratitis and sensorineural hearing loss (the **Hutchinson triad**).
- The symptoms described do not align with other features of congenital syphilis.
*Limb hypoplasia*
- **Limb hypoplasia** is a hallmark finding of **congenital varicella syndrome**, often associated with cutaneous scarring and ocular defects.
- It is not a typical manifestation of congenital CMV infection, which primarily affects the central nervous system, hematopoietic system, and growth.
Question 82: A 4-year-old girl is being followed by the pediatric oncology team after her pediatrician found a palpable abdominal mass towards the right flank 2 weeks ago. Abdominal ultrasonography detected a solid mass in the right kidney without infiltration of the renal vein and inferior vena cava. The contrast-enhanced computed tomography (CT) confirmed the presence of a solitary mass in the right kidney surrounded by a pseudocapsule consisting of a rim of normal tissue, displacing it medially, and distorting the collecting system. No nodal involvement was detected. In which of the following chromosomes would you expect a genetic abnormality?
A. Chromosome 13
B. Chromosome 1
C. Chromosome 3
D. Chromosome 22
E. Chromosome 11 (Correct Answer)
Explanation: ***Chromosome 11***
- This clinical presentation, particularly the **solitary renal mass** in a 4-year-old and the imaging findings of a **pseudocapsule** and displacement of the collecting system, is highly suggestive of **Wilms tumor (nephroblastoma)**.
- **Wilms tumor** is associated with genetic abnormalities, most notably mutations in the **WT1 gene** located on **chromosome 11p13**, and the **WT2 locus** on **chromosome 11p15.5**.
*Chromosome 13*
- Abnormalities on **chromosome 13** are primarily associated with **retinoblastoma**, linked to mutations in the **RB1 gene**.
- While retinoblastoma is a childhood cancer, its presentation involves ocular tumors, not renal masses.
*Chromosome 1*
- Genetic abnormalities on **chromosome 1** are implicated in various cancers and conditions, but they are not the primary or most characteristic genetic defect associated with **Wilms tumor**.
- Specific translocations or deletions on chromosome 1 can be seen in certain leukemias and lymphomas, which do not fit the clinical picture.
*Chromosome 3*
- **Chromosome 3** abnormalities are well-known in various malignancies, most notably **renal cell carcinoma (RCC)**, particularly the **von Hippel-Lindau (VHL) gene** at 3p25-26.
- RCC is typically a cancer of adulthood, and VHL disease presents with multiple organ system involvement, differing from a solitary renal mass in a young child.
*Chromosome 22*
- Abnormalities on **chromosome 22** are frequently associated with conditions like **neurofibromatosis type 2** (NF2 gene) and **DiGeorge syndrome** (22q11 deletion).
- The presentation of a renal mass in a child is not characteristic of genetic defects on chromosome 22.
Question 83: A 3175-g (7-lb) female newborn is delivered at term. Initial examination shows a distended abdomen and a flat perineal region without an opening. A dark green discharge is coming out of the vulva. Which of the following is the most likely diagnosis?
A. Hirschsprung disease
B. Meconium plug syndrome
C. Imperforate anus (Correct Answer)
D. Meconium ileus
E. Colonic atresia
Explanation: ***Imperforate anus***
- The combination of a **distended abdomen**, **flat perineal region without an opening**, and **dark green discharge from the vulva** (indicating meconium passage through a rectovaginal fistula) is pathognomonic for imperforate anus.
- This congenital anomaly results from abnormal development of the **hindgut** and **urogenital sinus**, leading to a spectrum of anorectal malformations.
*Hirschsprung disease*
- Characterized by the absence of **ganglion cells** in the distal colon, leading to functional obstruction.
- While it can cause **abdominal distension** and delayed meconium passage, it typically presents with a **normal-appearing anus** and no meconium from the vulva.
*Meconium plug syndrome*
- This is a transient obstruction of the colon by a **mucous plug**, without an anatomical defect of the anus.
- The anus would be **patent**, and though abdominal distension might occur, meconium would not be seen exiting the vulva.
*Meconium ileus*
- This condition involves obstruction of the **small bowel** by thick, inspissated meconium, primarily associated with **cystic fibrosis**.
- It would cause abdominal distension and delayed meconium passage, but the anus would be **patent**, and meconium would not be expelled through the vulva.
*Colonic atresia*
- This is a congenital complete obstruction of the colon, causing abdominal distension and vomiting.
- However, the **perineum would appear normal**, and there would be no meconium discharge from the vulva.
Question 84: A 7-year-old Caucasian girl with asthma presents to her pediatrician with recurrent sinusitis. The patient’s mother states that her asthma seems to be getting worse and notes that ‘lung problems run in the family’. The patient has had 2 episodes of pneumonia in the last year and continues to frequently have a cough. Her mother says that 1 of her nieces was recently diagnosed with cystic fibrosis. On physical examination, the child has clubbing of the nail beds on both hands. A chloride sweat test is performed on the patient, and the child’s sweat chloride concentration is found to be within normal limits. The physician is still suspicious for cystic fibrosis and believes the prior asthma diagnosis is incorrect. Which of the following diagnostic tests would aid in confirming this physician’s suspicions?
A. A urinalysis
B. A chest radiograph
C. A chest CT scan
D. A nasal transepithelial potential difference (Correct Answer)
E. A complete blood count
Explanation: ***A nasal transepithelial potential difference***
- This test directly measures the **ion transport** across the nasal epithelium, which is abnormal in cystic fibrosis due to **CFTR protein dysfunction**.
- It specifically assesses the ability of chloride channels to transport chloride ions, which helps diagnose **cystic fibrosis** even when sweat chloride tests are equivocal or normal, as might occur in some CFTR mutations.
*A urinalysis*
- A urinalysis assesses **kidney function** and detects urinary tract infections or metabolic disorders, which are not directly related to chronic respiratory or digestive issues seen in cystic fibrosis.
- While cystic fibrosis can cause complications like **nephrolithiasis** (kidney stones), a urinalysis is not a primary diagnostic tool for the disease itself.
*A chest radiograph*
- A chest radiograph can show changes associated with chronic lung disease like **hyperinflation**, **bronchial cuffing**, and **infiltrates** in cystic fibrosis, but it is not specific for confirming the diagnosis.
- It is often used for initial assessment and monitoring of lung disease progression, but does not provide definitive evidence of CFTR dysfunction.
*A chest CT scan*
- A chest CT provides more detailed images of the lungs, revealing abnormalities like **bronchiectasis**, **mucus plugging**, which are characteristic of advanced cystic fibrosis lung disease.
- However, like a chest radiograph, it shows the **consequences** of the disease rather than directly diagnosing the underlying CFTR defect, and it is not a primary diagnostic test for CF.
*A complete blood count*
- A CBC evaluates **blood components** (red cells, white cells, platelets) and can indicate general conditions like anemia or infection, which can be present in cystic fibrosis.
- It is a **nonspecific test** and does not provide any diagnostic information about the CFTR gene mutation or the underlying pathophysiology of cystic fibrosis.
Question 85: A 7-year-old boy is being evaluated in pediatric cardiology clinic. He appears grossly normal, but suddenly becomes tachypneic and cyanotic when his mom takes a toy away from him. These symptoms resolve somewhat when he drops into a squatting position. Transthoracic echocardiography reveals pulmonic stenosis, a ventricular septal defect, right ventricular hypertrophy, and an overriding aorta. Which of the following best predicts the degree of cyanosis and other hypoxemic symptoms in this patient?
A. Size of ventricular septal defect (VSD)
B. Degree of pulmonic stenosis (Correct Answer)
C. Degree of right ventricular hypertrophy (RVH)
D. Degree to which aorta overrides right ventricle
E. Presence of S3
Explanation: ***Degree of pulmonic stenosis***
- The **degree of pulmonic stenosis** is the primary determinant of right ventricular outflow obstruction, which dictates the amount of right-to-left shunting through the VSD and, consequently, the severity of cyanosis.
- More severe stenosis leads to higher right ventricular pressure, forcing a larger volume of deoxygenated blood into the aorta, thus increasing **hypoxemia** and **cyanosis**.
*Size of ventricular septal defect (VSD)*
- While a VSD is necessary for right-to-left shunting, its size primarily affects the magnitude of the shunt, but the **resistance to outflow** from the right ventricle (pulmonic stenosis) is the critical factor for cyanosis in Tetralogy of Fallot.
- A very small VSD in the presence of severe pulmonic stenosis would still result in significant right-to-left shunting.
*Degree of right ventricular hypertrophy (RVH)*
- **Right ventricular hypertrophy** is a compensatory response to the increased pressure load caused by pulmonic stenosis, but it is not the direct cause or primary predictor of cyanosis.
- RVH is a *consequence* of the obstruction, not the fundamental variable determining the severity of right-to-left shunting.
*Degree to which aorta overrides right ventricle*
- The **overriding aorta** allows for the mixing of deoxygenated blood from the right ventricle into the systemic circulation, but its degree of override does not independently determine the amount of deoxygenated blood shunted.
- The amount of blood flowing into the aorta from the right ventricle is primarily controlled by the outflow obstruction, not the aorta's position itself.
*Presence of S3*
- An **S3 heart sound** is typically associated with volume overload or ventricular dysfunction (e.g., congestive heart failure) and is not a characteristic finding or predictor of cyanosis in Tetralogy of Fallot.
- The key signs in Tetralogy of Fallot relating to cyanosis are often related to the right ventricular outflow obstruction.
Question 86: A 3400-g (7-lb 8-oz) female newborn is delivered at term to a 28-year-old primigravid woman. Apgar scores are 7 and 8 at 1 and 5 minutes, respectively. Vital signs are within normal limits. Examination shows swelling of bilateral upper and lower extremities and low-set ears. The posterior hair line is low and the chest appears broad. There are skin folds running down the sides of the neck to the shoulders. A grade 2/6 systolic ejection murmur and systolic click is heard at the apex. Which of the following is the most likely cause of this patient's swelling?
A. Renal retention of sodium
B. Impaired protein synthesis
C. Dysfunctional lymphatic system (Correct Answer)
D. Increased capillary permeability
E. Urinary protein loss
Explanation: ***Dysfunctional lymphatic system***
- The combination of **swelling of extremities**, **low-set ears**, **low posterior hairline**, **broad chest**, and **nuchal folds** (skin folds running down the sides of the neck) in a female newborn strongly points towards **Turner syndrome**.
- In Turner syndrome, **lymphedema** is common due to **lymphatic dysplasia**, leading to fluid accumulation and swelling in the affected areas.
*Renal retention of sodium*
- This would typically present with more **generalized edema** and signs of fluid overload, which are not specifically described in this localized manner.
- While possible in some conditions, other classic dysmorphic features presented in the vignette make this less likely.
*Impaired protein synthesis*
- **Hypoproteinemia**, due to impaired synthesis, can cause generalized edema, but it would not explain the specific dysmorphic features like low-set ears or nuchal folds seen in this patient.
- Conditions causing impaired protein synthesis are often related to liver dysfunction or severe malnutrition.
*Increased capillary permeability*
- This can lead to edema, often seen in conditions like **sepsis** or **anaphylaxis**, causing a rapid and generalized fluid shift from capillaries into the interstitial space.
- It does not account for the characteristic dysmorphic features and chronic nature of the swelling often associated with the underlying genetic condition.
*Urinary protein loss*
- Significant urinary protein loss (e.g., in **nephrotic syndrome**) leads to **hypoalbuminemia** and subsequent generalized edema.
- Similar to impaired protein synthesis, this mechanism would not explain the specific dysmorphic features observed in the newborn.
Question 87: A 2-hours-old neonate is found to have bluish discoloration throughout his body, including lips and tongue. The boy was born at 39 weeks gestation via spontaneous vaginal delivery with no prenatal care. Maternal history is positive for type 2 diabetes mellitus for 11 years. On physical examination, his blood pressure is 55/33 mm Hg, his heart rate is 150/min, respiratory rate is 45/min, temperature of 37°C (98.6°F), and oxygen saturation is 84% on room air. Appropriate measures are taken. Auscultation of the chest reveals a single second heart sound without murmurs. Chest X-ray is shown in the exhibit. Which of the following is the most likely diagnosis?
A. Esophageal atresia
B. Arteriovenous malformation
C. Tetralogy of Fallot
D. Transposition of great vessels (Correct Answer)
E. Congenital diaphragmatic hernia
Explanation: ***Transposition of great vessels***
- This condition presents with **severe cyanosis** that is unresponsive to oxygen, a **single S2**, and no murmur (often due to lack of significant shunting). The **chest X-ray findings** of an "egg-on-a-string" heart with a narrow mediastinum are characteristic due to the abnormal great artery positions.
- **Maternal diabetes** is a known risk factor for congenital heart defects, including transposition of the great arteries (TGA).
*Esophageal atresia*
- This condition presents with **feeding difficulties**, **choking**, and **respiratory distress** due to aspiration, not primarily severe cyanosis from cardiac causes.
- While it can manifest early, there are no specific cardiac findings or X-ray features of TGA.
*Arteriovenous malformation*
- An arteriovenous malformation would typically cause **high-output cardiac failure** or localized symptoms depending on its location, rather than generalized severe cyanosis like in this case.
- It does not present with the characteristic cardiac findings or X-ray features seen here.
*Tetralogy of Fallot*
- While Tetralogy of Fallot also causes **cyanosis**, it usually presents with a **harsh systolic murmur** due to pulmonary stenosis and a "boot-shaped" heart on X-ray, which are absent in this presentation.
- Cyanosis in Tetralogy of Fallot can worsen with crying or feeding, but the immediate severe cyanosis with a single S2 and no murmur points away from this diagnosis.
*Congenital diaphragmatic hernia*
- This condition presents with **severe respiratory distress** and **scaphoid abdomen** due to abdominal contents displacing lung tissue.
- While it can cause cyanosis due to pulmonary hypoplasia, it would not typically present with the specific cardiac findings (single S2, no murmur) or the X-ray appearance of an "egg-on-a-string" heart.
Question 88: A 2-year-old boy is brought in to the pediatrician by his mother because she is concerned that he is not gaining weight. She reports that the patient has a good appetite, eats a varied diet of solid foods, and drinks 2 cups of milk a day. The patient's mother also reports that he has foul-smelling stools over 6 times a day. The patient has a history of recurrent bronchiectasis and chronic sinusitis. On physical examination, multiple nasal polyps are appreciated and scattered rhonchi are heard over both lung fields. The patient is below the 25th percentile in height and weight. Genetic testing is ordered to confirm the suspected diagnosis. Which of the following is the most common complication associated with the patient's most likely diagnosis?
A. Inferior lens dislocation
B. Lymphoma
C. Meconium ileus
D. Infertility (Correct Answer)
E. Asthma
Explanation: ***Infertility***
- **Infertility** is the **most common long-term complication** in patients with **cystic fibrosis**, affecting **95-98% of males** due to **congenital bilateral absence of the vas deferens (CBAVD)**.
- Approximately **20% of females** with CF also experience reduced fertility due to thick cervical mucus.
- While not immediately evident in a 2-year-old, it is the most statistically prevalent complication when considering the lifetime course of the disease.
*Inferior lens dislocation*
- **Inferior lens dislocation** is characteristic of **homocystinuria**, a disorder of methionine metabolism, and is not associated with cystic fibrosis.
- Other features of homocystinuria include skeletal abnormalities (Marfanoid habitus), intellectual disability, and thrombotic events.
*Lymphoma*
- **Lymphoma** is a malignancy of the **lymphatic system** and is not a common complication directly associated with cystic fibrosis.
- While chronic inflammation found in CF could theoretically increase cancer risk, lymphoma is not a characteristic or common CF-related malignancy.
*Meconium ileus*
- **Meconium ileus** occurs in approximately **15-20% of CF patients** and presents **at birth or in the neonatal period** due to thickened meconium obstructing the intestines.
- While it is an important CF-related complication, it is **less common than infertility** (which affects 95%+ of patients) and would have already occurred in this 2-year-old patient if present.
- The question asks for the "most common complication," making infertility the correct answer based on prevalence.
*Asthma*
- While **asthma** can cause respiratory symptoms, CF-related lung disease is distinct, involving chronic infection, inflammation, and bronchiectasis due to thick mucus, rather than reversible airway hyperreactivity characteristic of asthma.
- The severe, progressive nature of the respiratory disease (recurrent bronchiectasis, chronic sinusitis, nasal polyps, rhonchi) and the malabsorption point specifically to **cystic fibrosis**, not typical asthma.
Question 89: A 6-year-old boy is brought to the physician by his mother who is concerned about his early sexual development. He has no history of serious illness and takes no medications. He is at the 99th percentile for height and 70th percentile for weight. His blood pressure is 115/78 mm Hg. Examination shows greasy facial skin and cystic acne on his forehead and back. There is coarse axillary and pubic hair. Serum studies show:
Cortisol (0800 h) 4 μg/dL
Deoxycorticosterone 2.5 ng/dL (N = 3.5–11.5)
Dehydroepiandrosterone sulfate 468 mcg/dL (N = 29–412)
Which of the following is the most likely underlying cause of this patient's symptoms?
A. Deficiency of 21β-hydroxylase (Correct Answer)
B. Idiopathic overproduction of GnRH
C. Constitutive activation of adenylyl cyclase
D. Deficiency of 11β-hydroxylase
E. Deficiency of 17α-hydroxylase
Explanation: ***Deficiency of 21β-hydroxylase***
- The combination of **precocious puberty** (early sexual development, acne, coarse hair), elevated **DHEA-S**, and low **cortisol** with **low-normal DOC** confirms 21β-hydroxylase deficiency, causing **congenital adrenal hyperplasia (CAH)**.
- This enzyme deficiency blocks cortisol and aldosterone synthesis, shunting precursors towards **androgen production**, causing **adrenal androgen excess** and virilization.
- The **low DOC level (2.5 ng/dL, below normal 3.5-11.5)** is the key finding that distinguishes this from 11β-hydroxylase deficiency.
- The mild hypertension may be due to increased androgen-mediated effects or represents an atypical presentation.
*Idiopathic overproduction of GnRH*
- This would cause **central precocious puberty**, characterized by activation of the **hypothalamic-pituitary-gonadal axis** (HPGA).
- While it causes precocious puberty, it would not typically lead to isolated elevation of **adrenal androgens** like DHEA-S with concurrent low cortisol, which points to an adrenal rather than central cause.
- Laboratory findings would show elevated LH, FSH, and gonadal sex steroids rather than adrenal androgens.
*Constitutive activation of adenylyl cyclase*
- This is linked to conditions like **McCune-Albright syndrome**, which can cause peripheral precocious puberty but typically presents with the classic triad: **café-au-lait spots**, **fibrous dysplasia of bone**, and **autonomous endocrine hyperfunction**.
- The hormonal profile reflects the specific endocrine gland involved (often gonadal), not the pattern of **adrenal androgen excess** with low cortisol and low DOC seen here.
*Deficiency of 11β-hydroxylase*
- This is the second most common cause of CAH and also causes adrenal androgen excess leading to virilization and precocious puberty.
- However, 11β-hydroxylase deficiency results in **accumulation of deoxycorticosterone (DOC)**, which causes **hypertension** and **hypokalemia**.
- This patient's **DOC is LOW (2.5 ng/dL, below normal range 3.5-11.5)**, which definitively rules out this diagnosis despite the presence of hypertension.
*Deficiency of 17α-hydroxylase*
- This deficiency impairs synthesis of **cortisol** and **sex steroids**, but increases production of mineralocorticoids (DOC and corticosterone).
- Patients present with **hypertension**, **hypokalemia**, sexual infantilism, and in XY individuals, **female external genitalia** due to lack of androgens.
- This is the opposite of the **virilization and elevated DHEA-S** seen in this patient.
Question 90: An 8-year-old girl is brought to the physician because of a progressive swelling of her neck for the past 6 months. She has no pain, dyspnea, or dysphagia. She is at the 60th percentile for height and the 55th percentile for weight. Vital signs are within normal limits. Examination shows a 3-cm cystic, nontender swelling in the midline of the neck. The swelling moves upwards on protrusion of the tongue. There is no cervical lymphadenopathy. Her serum thyroid-stimulating hormone level is 2.1 μU/mL. Which of the following is the most appropriate next step in management?
A. Excision of the cyst
B. Excision of the cyst, track and hyoid bone
C. Thyroid scintigraphy
D. Ultrasonography of the neck (Correct Answer)
E. CT scan of the neck
Explanation: ***Ultrasonography of the neck***
- The presentation of a **midline cystic neck mass** in a child that moves with **tongue protrusion** is classic for a **thyroglossal duct cyst**.
- **Ultrasonography** is the preferred initial imaging modality to confirm the cystic nature, rule out other neck masses, and importantly, verify the presence of a **normally located thyroid gland** to ensure the cyst is not the only functional thyroid tissue.
*Excision of the cyst*
- While ultimately surgical excision is the definitive treatment for a thyroglossal duct cyst, it is not the most appropriate *next step in management* before imaging is performed.
- **Pre-operative imaging** (especially ultrasound) is crucial to differentiate the cyst from other neck masses and confirm the presence of a normally located thyroid gland, which influences surgical planning.
*Excision of the cyst, track, and hyoid bone*
- This describes the **Sistrunk procedure**, which is the definitive surgical management for a thyroglossal duct cyst and has a lower recurrence rate.
- However, performing this procedure without prior imaging to confirm the diagnosis and the presence of a functional thyroid gland would be premature and potentially unsafe.
*Thyroid scintigraphy*
- **Thyroid scintigraphy** would be considered if there is suspicion that the cyst contains ectopic thyroid tissue or if ultrasonography fails to identify a normally located thyroid gland.
- It is not typically the first-line imaging study but may be used when there are concerns about the functional status or location of the thyroid gland.
*CT scan of the neck*
- A **CT scan of the neck** would involve radiation exposure and is generally reserved for cases where the diagnosis is unclear after ultrasound, or if there's suspicion of malignancy or involvement of deeper structures.
- For a suspected thyroglossal duct cyst, **ultrasound** is sufficient and safer as the initial imaging choice.
