Rhabdomyosarcoma US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Rhabdomyosarcoma. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Rhabdomyosarcoma US Medical PG Question 1: A 33-year-old woman comes to the physician 1 week after noticing a lump in her right breast. Fifteen years ago, she was diagnosed with osteosarcoma of her left distal femur. Her father died of an adrenocortical carcinoma at the age of 41 years. Examination shows a 2-cm, firm, immobile mass in the lower outer quadrant of the right breast. A core needle biopsy of the mass shows adenocarcinoma. Genetic analysis in this patient is most likely to show a defect in which of the following genes?
- A. BRCA1
- B. KRAS
- C. TP53 (Correct Answer)
- D. Rb
- E. PTEN
Rhabdomyosarcoma Explanation: ***TP53***
- This patient's presentation with **early-onset breast cancer**, a history of **osteosarcoma** at a young age, and a father's death from **adrenocortical carcinoma** at 41 years strongly suggests **Li-Fraumeni syndrome**.
- Li-Fraumeni syndrome is an autosomal dominant disorder caused by a germline mutation in the **tumor suppressor gene TP53**, increasing the risk for multiple primary cancers at a young age.
*BRCA1*
- While **BRCA1 mutations** are associated with an increased risk of breast and ovarian cancer, they are not typically linked to osteosarcoma or adrenocortical carcinoma.
- The constellation of cancers in this patient is more indicative of Li-Fraumeni syndrome than solely a BRCA1-related cancer syndrome.
*KRAS*
- **KRAS** is an oncogene commonly mutated in several cancers, including pancreatic, colorectal, and lung cancer, but is not primarily associated with either Li-Fraumeni syndrome or the specific tumors seen in this family history.
- Mutations in KRAS are typically somatic mutations acquired during a person's lifetime, not germline mutations causing inherited cancer syndromes like the one suggested here.
*Rb*
- Mutations in the **retinoblastoma (Rb) gene** are associated with retinoblastoma and an increased risk of osteosarcoma, but not typically with adrenocortical carcinoma or breast cancer as part of a classic inherited syndrome.
- The combination of breast cancer, osteosarcoma, and adrenocortical carcinoma points more specifically to TP53.
*PTEN*
- **PTEN mutations** are associated with Cowden syndrome, which increases the risk for breast cancer, thyroid cancer, and endometrial cancer, along with benign growths.
- However, Cowden syndrome does not typically include osteosarcoma or adrenocortical carcinoma as prominent features, making PTEN less likely than TP53 for this specific family history.
Rhabdomyosarcoma US Medical PG Question 2: An 82-year-old woman presents to the emergency department because of excruciating right flank pain and fever for the past 2 days. She states that she is having trouble urinating. Her past medical history is unremarkable. A urinalysis is performed and comes back positive for leukocytes and gram-negative bacilli. A contrast computed tomography of the abdomen is performed and reveals a large retroperitoneal mass compressing the right ureter, leading to hydronephrosis of the right kidney. The mass is excised. Histopathologic evaluation of the mass is shown in the image below, and it is determined to be malignant. Which of the following is the most likely diagnosis in this patient?
- A. Rhabdomyosarcoma
- B. Leiomyosarcoma
- C. Lipoma
- D. Teratoma
- E. Liposarcoma (Correct Answer)
Rhabdomyosarcoma Explanation: ***Liposarcoma***
- The **most common primary malignant retroperitoneal tumor** in adults, particularly in elderly patients
- Characteristically presents as a **large retroperitoneal mass** causing compressive symptoms such as hydronephrosis
- **Histopathological features** include pleomorphic lipoblasts with varying degrees of differentiation (well-differentiated, dedifferentiated, myxoid, or pleomorphic subtypes)
- The clinical presentation of an elderly patient with a malignant retroperitoneal mass strongly suggests this diagnosis
*Rhabdomyosarcoma*
- Primarily a **pediatric malignancy**, most common in children and young adults under 20 years old
- Most frequently arises in the **head and neck, genitourinary tract, or extremities**, not typically retroperitoneal
- Histologically shows skeletal muscle differentiation with rhabdomyoblasts, not lipoblastic features
*Leiomyosarcoma*
- More commonly found in the **uterus, gastrointestinal tract, or blood vessels**
- While it can occur in the retroperitoneum, it is **less common** than liposarcoma in this location
- Histologically demonstrates **smooth muscle differentiation** with spindle cells, not the lipoblastic features characteristic of the described mass
*Lipoma*
- A **benign tumor** composed of mature adipose tissue without cellular atypia
- Would not present as a **malignant mass** on histopathologic evaluation
- Generally asymptomatic and slow-growing; unlikely to cause severe symptoms like excruciating pain or obstructive hydronephrosis
*Teratoma*
- Contains tissue derived from **all three germ layers** (ectoderm, mesoderm, endoderm)
- More commonly associated with **gonadal or midline structures** (ovaries, testes, mediastinum)
- Rare in the retroperitoneum in elderly patients; histology would show diverse tissue types rather than predominantly lipoblastic features
Rhabdomyosarcoma US Medical PG Question 3: A 67-year-old man is referred to a dermatologist after a reddish mole appears on his nose. The mole’s size has changed over the last 2 years, and occasional bleeding is noted. The man’s medical history is unremarkable, and he does not take any medications. He retired from his construction job 15 years ago. Physical examination of his nose reveals a 2-cm pink papule with a pearly appearance and overlying telangiectasia on the ala of the nose (see image). Which of the following would be the best treatment modality if surgery is not an option?
- A. Radiation therapy (Correct Answer)
- B. Imiquimod
- C. Interferon
- D. 5-fluorouracil
- E. Photodynamic therapy
Rhabdomyosarcoma Explanation: ***Radiation therapy***
- This patient's presentation is highly suggestive of **basal cell carcinoma (BCC)**, given the reddish, pearly papule with telangiectasias on a sun-exposed area, a history of growth over two years, bleeding, and his prior occupation as a construction worker. **Radiation therapy** is an excellent option for **localized BCC** when surgery is contraindicated or not feasible due to patient preferences, tumor location (e.g., cosmetic areas), or medical comorbidities.
- **Definitive radiation therapy** can achieve high cure rates for BCC, comparable to Mohs surgery for appropriately selected superficial and nodular types, and is particularly useful in older patients.
*Imiquimod*
- **Imiquimod** is an **immune-response modifier** used topically for superficial BCCs, actinic keratoses, and external genital warts.
- While effective for **superficial BCCs**, its efficacy is lower for nodular or infiltrative BCCs, which appears more likely given the size (2 cm) and depth implied by chronic bleeding and growth over 2 years.
*Interferon*
- **Interferon** has been explored as an intralesional treatment for BCC, but it is **not a first-line or standard treatment option** due to variable response rates and the availability of more effective and reliable modalities.
- Its use is generally reserved for more advanced or difficult-to-treat cases, typically as part of clinical trials or for very specific indications, not as a primary treatment for a localized BCC where surgery or radiation is an option.
*5-fluorouracil*
- **5-fluorouracil (5-FU)** is a **topical chemotherapeutic agent** used primarily for **actinic keratoses** and **superficial BCCs**.
- Similar to imiquimod, its efficacy is limited to **superficial lesions** and is less effective for nodular, infiltrative, or larger BCCs due to insufficient penetration and risk of recurrence.
*Photodynamic therapy*
- **Photodynamic therapy (PDT)** involves applying a photosensitizing agent followed by exposure to specific wavelengths of light, primarily used for **actinic keratoses** and **superficial BCCs**.
- While effective for superficial lesions, its efficacy significantly decreases for **nodular BCCs** or those with deeper invasion, making it less suitable for a 2 cm lesion that has been growing and bleeding.
Rhabdomyosarcoma US Medical PG Question 4: A 70-year-old man comes to the physician because of progressive fatigue and lower back pain for the past 4 months. The back pain worsened significantly after he had a minor fall while doing yard work the previous day. For the past year, he has had a feeling of incomplete emptying of his bladder after voiding. His vital signs are within normal limits. Examination shows bilateral paravertebral muscle spasm, severe tenderness over the second lumbar vertebra, and mild tenderness over the lower thoracic vertebrae. Neurologic examination shows no abnormalities. His hemoglobin is 10.5 g/dl, alkaline phosphatase is 110 U/L, and serum calcium is 11.1 mg/dl. An x-ray of the skull is shown. Which of the following is the most appropriate next step in diagnosis?
- A. Bone marrow biopsy
- B. Bone scan
- C. Serum vitamin D levels
- D. Prostate biopsy
- E. Serum protein electrophoresis (Correct Answer)
Rhabdomyosarcoma Explanation: ***Serum protein electrophoresis***
- The patient's symptoms (fatigue, back pain with minor fall causing vertebral tenderness), laboratory findings (**anemia**, **hypercalcemia**), and especially the skull X-ray showing **numerous lytic lesions** (also known as "punched-out" lesions) are highly suggestive of **multiple myeloma**.
- **Serum protein electrophoresis** (SPEP) is the most appropriate next step as it is crucial for identifying and quantifying the **monoclonal protein (M-spike)** produced by plasma cells, which is diagnostic for multiple myeloma.
*Bone marrow biopsy*
- While a bone marrow biopsy is used to confirm the diagnosis of multiple myeloma by identifying **clonal plasma cells**, it is typically done after initial screening tests like SPEP strongly suggest the diagnosis.
- SPEP is a less invasive and often the first definitive diagnostic step before proceeding to bone marrow biopsy.
*Bone scan*
- **Bone scans (technetium-99m scintigraphy)** are generally not useful for detecting the purely **lytic lesions** characteristic of multiple myeloma, as these lesions do not involve increased osteoblastic activity (bone formation) which is necessary for tracer uptake.
- X-rays and MRI are more effective for visualizing lytic lesions in multiple myeloma.
*Serum vitamin D levels*
- While vitamin D levels are important for bone health, measuring them is not a primary diagnostic step in a suspected case of multiple myeloma.
- The patient's symptoms and signs point strongly towards a neoplastic process, not a primary vitamin D deficiency.
*Prostate biopsy*
- The patient's age and urinary symptoms (incomplete bladder emptying) could raise suspicion for **prostatic enlargement** (benign prostatic hyperplasia or prostate cancer). However, the prominent lytic bone lesions, hypercalcemia, and anemia point more definitively towards a systemic hematologic malignancy like multiple myeloma rather than metastatic prostate cancer.
- While prostate cancer can cause blastic bone metastases, the X-ray shows classic lytic lesions, which are less typical of prostate cancer metastases and more characteristic of multiple myeloma.
Rhabdomyosarcoma US Medical PG Question 5: An investigator studying the molecular characteristics of various malignant cell lines collects tissue samples from several families with a known mutation in the TP53 tumor suppressor gene. Immunohistochemical testing performed on one of the cell samples stains positive for desmin. This sample was most likely obtained from which of the following neoplasms?
- A. Squamous cell carcinoma
- B. Rhabdomyosarcoma (Correct Answer)
- C. Prostate cancer
- D. Endometrial carcinoma
- E. Melanoma
Rhabdomyosarcoma Explanation: ***Rhabdomyosarcoma***
- **Desmin** is an intermediate filament present in **muscle cells**, and its positive staining is a definitive marker for tumors of muscle origin
- A **rhabdomyosarcoma** is a malignant tumor of **skeletal muscle** differentiation, thus explaining the positive desmin staining.
*Squamous cell carcinoma*
- **Squamous cell carcinomas** are epithelial tumors that typically stain positive for **cytokeratin**, not desmin, as they originate from epithelial cells.
- They are characterized by features such as **intercellular bridges** and **keratinization**.
*Prostate cancer*
- **Prostate cancer** is an adenocarcinoma, meaning it's derived from glandular epithelial cells, and would stain positive for markers like **PSA (prostate-specific antigen)**, not desmin.
- This tumor type is characterized by glandular differentiation.
*Endometrial carcinoma*
- **Endometrial carcinomas** are adenocarcinomas of the uterine lining, derived from glandular epithelial cells, and would express **cytokeratins**, not desmin.
- Histologically, they show glandular structures and atypical endometrial cells.
*Melanoma*
- **Melanomas** are malignant tumors of melanocytes and would stain positive for markers such as **S-100**, **HMB-45**, and **Mart-1**, not desmin.
- These tumors originate from neural crest cells and are not muscle-derived.
Rhabdomyosarcoma US Medical PG Question 6: A 19-month-old girl is brought by her mother to the local walk-in clinic after noticing a mass protruding from her vagina. The mass had the appearance of "a bunch of grapes". She also says that she has been having a vaginal discharge for the past 6 months. Her family and personal history are not significant for malignancies or inherited disorders. The physical examination is unremarkable except for the presence of soft nodules protruding from the vaginal canal. A tissue sample is obtained for histologic evaluation. Several weeks later the patient returns to the walk-in clinic for a scheduled follow-up visit. The pathology report describes a polypoid mass beneath an epithelial surface with atypical stromal cells positive for polyclonal desmin. What is the most likely diagnosis in this patient?
- A. Squamous cell carcinoma (SCC)
- B. Verrucous carcinoma
- C. Sarcoma (Correct Answer)
- D. Adenocarcinoma
- E. Melanoma
Rhabdomyosarcoma Explanation: ***Sarcoma***
- The description of a **"bunch of grapes"** mass in a young girl, along with **atypical stromal cells** positive for **polyclonal desmin**, is highly characteristic of **embryonal rhabdomyosarcoma** (a type of sarcoma botryoides).
- **Desmin positivity** indicates a muscle cell origin, and the **polypoid mass** is consistent with the gross appearance of this aggressive childhood tumor.
*Squamous cell carcinoma (SCC)*
- SCC of the vagina is extremely rare in a **19-month-old girl** and typically affects older women.
- Histologically, SCC would show **dysplastic squamous epithelial cells** with **keratinization** or intercellular bridges, not atypical stromal cells positive for desmin.
*Verrucous carcinoma*
- This is a rare, well-differentiated variant of SCC, also typically occurring in **older individuals** and associated with HPV infection.
- It presents as a **warty, exophytic lesion** with minimal cellular atypia, distinct from a "bunch of grapes" mass and desmin positivity.
*Adenocarcinoma*
- Vaginal adenocarcinoma can occur in young girls, particularly **clear cell adenocarcinoma** associated with **diethylstilbestrol (DES) exposure**; however, this patient has no such history.
- Histology would show glandular differentiation and mucin production, not atypical stromal cells expressing desmin.
*Melanoma*
- Vaginal melanoma is very rare, typically presenting as a **pigmented lesion** in postmenopausal women.
- Histopathology would reveal malignant melanocytes with **positive S-100 and HMB-45 staining**, not atypical stromal cells positive for desmin.
Rhabdomyosarcoma US Medical PG Question 7: An 8-year-old boy is brought to the physician by his mother because of a 3-week history of irritability and frequent bed wetting. She also reports that he has been unable to look upward without tilting his head back for the past 2 months. He is at the 50th percentile for height and weight. His vital signs are within normal limits. Ophthalmological examination shows dilated pupils that are not reactive to light and bilateral optic disc swelling. Pubic hair development is Tanner stage 2. The most likely cause of this patient's condition is a tumor in which of the following locations?
- A. Fourth ventricle
- B. Sella turcica
- C. Cerebellar vermis
- D. Cerebral falx
- E. Dorsal midbrain (Correct Answer)
Rhabdomyosarcoma Explanation: ***Dorsal midbrain***
- The inability to look upward (**Parinaud's syndrome**), dilated pupils with poor light reflex, and **optic disc swelling** (indicating increased intracranial pressure) are classic signs of a mass lesion compressing the **dorsal midbrain**, specifically the **tectal plate**.
- **Irritability and bedwetting** are nonspecific symptoms, but in this context, they could be related to **hydrocephalus** due to **aqueductal compression** by the tumor.
*Fourth ventricle*
- Tumors of the fourth ventricle typically present with symptoms related to **hydrocephalus** (headache, nausea, vomiting, papilledema) and **ataxia** due to cerebellar involvement, but not specifically with **Parinaud's syndrome**.
- **Truncal ataxia** and **gait instability** are common with posterior fossa tumors affecting the cerebellum.
*Sella turcica*
- Tumors in the sella turcica primarily affect the **pituitary gland** and **optic chiasm**, leading to **endocrine dysfunction** (e.g., growth retardation, precocious puberty, hypogonadism) and **bitemporal hemianopsia**.
- **Parinaud's syndrome** and **dilated, unreactive pupils** are not typical presentations for sellar tumors.
*Cerebral falx*
- Tumors associated with the cerebral falx (e.g., meningiomas) are often located **supratentorially** and can cause focal neurological deficits like **seizures** or **hemiparesis**, depending on their location and size.
- They do not typically cause the specific eye movement disorders or pupillary abnormalities seen in this patient.
*Cerebellar vermis*
- Cerebellar vermis tumors often lead to **truncal ataxia**, **gait disturbance**, and **hydrocephalus** due to compression of the aqueduct or fourth ventricle outflow.
- While they can cause increased intracranial pressure, they do not directly cause **Parinaud's syndrome** or isolated deficits of upward gaze.
Rhabdomyosarcoma US Medical PG Question 8: A 45-year-old man with HIV comes to the physician because of multiple lesions on his chest and lower extremities. The lesions have progressively increased in size and are not painful or pruritic. Current medications include abacavir, dolutegravir, and lamivudine. A photograph of the lesions is shown. His CD4+ T-lymphocyte count is 450/mm3 (normal ≥ 500/mm3). A skin biopsy shows multiple spindle-shaped cells and lymphocytic infiltrate. Which of the following is the most appropriate pharmacotherapy?
- A. Ganciclovir
- B. Amphotericin B
- C. Alpha-interferon (Correct Answer)
- D. Doxycycline
- E. Nitazoxanide
Rhabdomyosarcoma Explanation: ***Alpha-interferon***
- This patient's presentation with **multiple skin lesions** in the setting of **HIV infection** and a **CD4+ count of 450/mm3** is highly suggestive of **Kaposi's sarcoma (KS)**. The biopsy findings of **spindle-shaped cells** and **lymphocytic infiltrate** further support this diagnosis. Though chemotherapy regimens are common for widespread KS, **alpha-interferon** is an appropriate treatment for **localized or less aggressive KS**, especially given his relatively preserved immune status (CD4+ count).
- Alpha-interferon exerts **antineoplastic effects** by inhibiting cell proliferation and stimulating host immune responses against tumor cells, making it suitable for managing KS.
*Ganciclovir*
- **Ganciclovir** is an antiviral agent primarily used for the treatment of **cytomegalovirus (CMV) infections**, such as retinitis or colitis, especially in immunocompromised patients.
- The patient's symptoms are not consistent with CMV disease, and the biopsy findings point away from a viral infection typically treated by ganciclovir.
*Amphotericin B*
- **Amphotericin B** is a broad-spectrum antifungal medication used to treat severe, **invasive fungal infections** like candidiasis, aspergillosis, or cryptococcosis.
- The clinical presentation and biopsy results (spindle cells, lymphocytic infiltrate) do not indicate a fungal etiology.
*Doxycycline*
- **Doxycycline** is a tetracycline antibiotic with broad antibacterial activity, used for infections like Lyme disease, chlamydia, or acne. It also has anti-inflammatory properties but is not a primary treatment for Kaposi's sarcoma.
- While some research explores its potential in KS due to its anti-angiogenic properties, it is not considered first-line pharmacotherapy for established Kaposi's sarcoma at this stage.
*Nitazoxanide*
- **Nitazoxanide** is an antiparasitic medication used to treat certain parasitic infections, such as cryptosporidiosis and giardiasis.
- The patient's symptoms and biopsy findings are not indicative of a parasitic infection.
Rhabdomyosarcoma US Medical PG Question 9: An 18-month-old boy is brought to the doctor’s office for evaluation of abdominal pain. The boy looks emaciated and he is now significantly below his growth chart predicted weight. The family history is non-contributory. The vital signs are unremarkable. On physical examination, a non-tender mass is felt in the upper part of the abdomen. A magnetic resonance image (MRI) scan of his abdomen demonstrates a mass in his right adrenal gland. Biopsy of the mass demonstrates an abundance of small round blue cells. With this biopsy result, which 1 of the following findings would confirm the diagnosis?
- A. Elevation of vanillylmandelic acid in the urine (Correct Answer)
- B. MRI showing the intrarenal origin of the mass
- C. Increased lactic dehydrogenase
- D. Increased alpha-fetoprotein
- E. Radiograph of the bone showing the presence of lytic bone lesion with periosteal reaction
Rhabdomyosarcoma Explanation: ***Elevation of vanillylmandelic acid in the urine***
- The clinical presentation (abdominal mass, emaciation, age) and biopsy finding of **small round blue cells** in the adrenal gland are highly suggestive of **neuroblastoma**.
- **Neuroblastomas** arise from neural crest cells and characteristically produce **catecholamines**, leading to elevated urinary levels of their metabolites like **vanillylmandelic acid (VMA)** and **homovanillic acid (HVA)**.
*MRI showing the intrarenal origin of the mass*
- An **intrarenal origin** of the mass would suggest a **Wilms tumor** (nephroblastoma), which is another common pediatric abdominal malignancy.
- However, the mass is described as being in the **adrenal gland**, and the biopsy shows small round blue cells, which are characteristic of neuroblastoma rather than Wilms tumor.
*Increased lactic dehydrogenase*
- Elevated **lactic dehydrogenase (LDH)** is a non-specific tumor marker often associated with a high tumor burden and rapid cell turnover in various malignancies, including neuroblastoma.
- While it can be elevated in neuroblastoma, it is not a specific diagnostic marker and would not confirm the diagnosis over other pediatric cancers.
*Increased alpha-fetoprotein*
- Elevated **alpha-fetoprotein (AFP)** is primarily associated with **hepatoblastoma** and **germ cell tumors**.
- It is not typically elevated in neuroblastoma and would therefore not confirm this diagnosis.
*Radiograph of the bone showing the presence of lytic bone lesion with periosteal reaction*
- While **neuroblastoma** can metastasize to bones, causing **lytic bone lesions** and a periosteal reaction, these findings indicate metastatic disease rather than confirming the primary diagnosis.
- A bone radiograph showing such lesions points to advanced disease but doesn't specifically confirm neuroblastoma as the primary tumor type.
Rhabdomyosarcoma US Medical PG Question 10: A 1-month-old boy is brought to the physician because of a 5-day history of generalized fatigue and multiple episodes of vomiting which is most pronounced after formula feeding. His vomiting progressed from 2–3 episodes on the first day to 6–8 episodes at present. The vomitus is whitish in color. The mother reports that he has been very hungry after each episode of vomiting. The patient was born at 38 weeks' gestation and weighed 3100 g (6 lb 13 oz); he currently weighs 3500 g (7 lb 11 oz). He appears irritable. His temperature is 37.1°C (98.8°F), pulse is 130/min, respirations are 43/min, and blood pressure is 74/36 mm Hg. Examination shows dry mucous membranes. The abdomen is soft and not distended. There is a round mass palpable in the epigastric region. The liver is palpated 1 cm below the right costal margin. Laboratory studies show:
Hemoglobin 15.3 g/dL
Leukocyte count 6300/mm3
Platelet count 230,000/mm3
Serum
Na+ 133 mEq/L
K+ 3.4 mEq/L
Cl- 92 mEq/L
Glucose 77 mg/dL
Creatinine 1.0 mg/dL
A urinalysis shows a decreased pH. Which of the following is the most appropriate next step in the management of this patient?
- A. Measure serum cortisol levels
- B. Perform upper GI endoscopy
- C. Administer IV 0.9% NaCl and replace electrolytes (Correct Answer)
- D. Perform emergency pyloromyotomy
- E. Obtain CT scan of the abdomen with contrast
Rhabdomyosarcoma Explanation: ***Administer IV 0.9% NaCl and replace electrolytes***
- The patient exhibits signs of **dehydration** (dry mucous membranes, irritability) and **hypochloremic metabolic alkalosis** (low Na+ 133, K+ 3.4, Cl- 92) secondary to persistent vomiting.
- The clinical presentation strongly suggests **pyloric stenosis** (progressive non-bilious vomiting, palpable epigastric mass, hungry after vomiting), but the patient's **electrolyte imbalances and dehydration must be corrected before any surgical intervention** to minimize operative risks.
- The paradoxical aciduria (decreased urine pH) occurs because severe volume depletion triggers aldosterone secretion, leading to preferential H+ excretion over HCO3- despite metabolic alkalosis.
*Measure serum cortisol levels*
- While adrenal insufficiency can cause vomiting and electrolyte abnormalities, the specific presentation of **non-bilious vomiting** with an **epigastric mass** and **hunger after vomiting** strongly points to **pyloric stenosis**.
- There are no other clear signs of adrenal insufficiency such as **hyperpigmentation**, **significant hypoglycemia**, or **hyperkalemia** that would make this the immediate priority over correcting dehydration and electrolytes.
*Perform upper GI endoscopy*
- Upper GI endoscopy is primarily used to visualize the upper digestive tract for conditions like **esophagitis**, **gastritis**, or **ulcers**.
- It is not the initial diagnostic test for **pyloric stenosis**; an **abdominal ultrasound** is preferred for confirming the diagnosis (showing pyloric wall thickness >3mm and channel length >15mm).
- Correcting the patient's severe dehydration and electrolyte imbalances takes precedence over diagnostic procedures.
*Perform emergency pyloromyotomy*
- Although pyloric stenosis is strongly suspected and **pyloromyotomy** is the definitive treatment, it is an elective surgical procedure.
- The patient is currently **dehydrated** with **electrolyte abnormalities** (hypochloremic, hypokalemic metabolic alkalosis), which must be corrected *before* surgery to minimize anesthetic and surgical risks and improve outcomes.
- Pyloric stenosis is **not a surgical emergency**; stabilization always precedes surgery.
*Obtain CT scan of the abdomen with contrast*
- A CT scan uses **ionizing radiation** and **contrast agents**, which are generally avoided in infants unless absolutely necessary.
- An **abdominal ultrasound** is the diagnostic study of choice for **pyloric stenosis** due to its non-invasiveness, lack of radiation exposure, and effectiveness in identifying the characteristic hypertrophied pylorus ("olive" or "target sign").
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