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Difficulty: MediumPediatric Hematology and Oncology

A 24-month-old toddler is brought to the pediatric clinic by her parents, who noticed an unusual lump in her abdomen while dressing her. Over the past month, the child has been increasingly fussy, has experienced intermittent bone pain, and has lost a noticeable amount of weight. Vital signs show a temperature of 37.2°C (99.0°F), a heart rate of 115/min, and a blood pressure of 138/88 mmHg. Physical examination reveals a firm, irregular, nodular abdominal mass that extends across the anatomic midline. Additional findings include bilateral periorbital ecchymoses and a right-sided mild ptosis with miosis. Which of the following laboratory studies is most appropriate to help confirm this patient's most likely diagnosis?

  1. A
    Measurement of plasma free metanephrines
  2. B
    Serum alpha-fetoprotein level
  3. Measurement of urinary homovanillic acid and vanillylmandelic acidAnswer
  4. D
    Complete blood count with peripheral smear
  5. E
    Urinalysis for microscopic hematuria

Answer

The correct answer is the measurement of urinary homovanillic acid and vanillylmandelic acid, which confirms the diagnosis of neuroblastoma.
The correct answer identifies the measurement of urinary homovanillic acid (HVA) and vanillylmandelic acid (VMA). The patient's presentation—a firm, nodular abdominal mass crossing the midline, elevated blood pressure, periorbital ecchymoses ('raccoon eyes'), and Horner syndrome (ptosis and miosis)—is classic for neuroblastoma. This embryonal tumor of neural crest origin frequently secretes catecholamines. Detecting elevated levels of their urinary metabolites, HVA and VMA, is highly specific and represents the most appropriate initial biochemical test to confirm the diagnosis.

Step-by-Step Solution

1
Identify the clinical syndrome based on the physical exam findings.
The firm, nodular abdominal mass crossing the midline, combined with periorbital ecchymoses and Horner syndrome, strongly suggests neuroblastoma.
Wilms tumor typically does not cross the midline and lacks these specific metastatic and sympathetic chain signs.
2
Determine the biochemical signature of the suspected tumor.
Neuroblastomas are derived from primitive sympathetic ganglion cells and actively secrete catecholamines.
Identifying the metabolic byproducts of these catecholamines is the standard biochemical diagnostic step.
3
Select the appropriate laboratory test from the given options.
Measuring urinary homovanillic acid (HVA) and vanillylmandelic acid (VMA) is the best choice.
HVA and VMA are the primary breakdown products of dopamine and norepinephrine, respectively, which are secreted by neuroblastomas.

Key Concept

Diagnosis of pediatric neuroblastoma relies on identifying its unique clinical presentation (a firm abdominal mass often crossing the midline, sympathetic chain involvement, and orbital metastases) and confirming via elevated urinary catecholamine metabolites (HVA and VMA).
Estimated Time:1m 30s
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Topics

Pediatric Hematology and Oncology

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