What is the most likely diagnosis for a patient with a painless abdominal mass?

Neuroblastoma is the Most Likely Diagnosis

In a patient presenting with a painless abdominal mass, neuroblastoma is the most likely diagnosis, particularly in the pediatric population where it represents the most common extracranial solid malignancy and characteristically presents as an abdominal mass or distension. 1, 2

Clinical Presentation Supporting Neuroblastoma

• Abdominal mass or distension is the most common presenting feature of neuroblastoma, occurring in the majority of cases 1
• The mass is typically painless initially, distinguishing it from inflammatory or infectious processes 3
• Neuroblastoma accounts for 7% of all childhood malignancies and is the most frequent abdominal malignancy in children after Wilms' tumor 4, 2
• The tumor arises from neural crest cells and most commonly occurs in the retroperitoneum and adrenal glands 5, 6

Why Not the Other Options

Wilms Tumor (Not Listed but Common Differential)

• While Wilms' tumor also presents as an abdominal mass, neuroblastoma is more likely to present with systemic symptoms and crosses the midline on imaging, whereas Wilms' tumor typically remains confined to one side 2

Hepatoblastoma

• Hepatoblastoma specifically presents as a hepatic mass with upper abdominal fullness 2
• It is less common than neuroblastoma overall and has a more specific anatomic location (liver) 2
• The question asks about a general "abdominal mass" without specifying hepatic origin, making neuroblastoma more likely

Diagnostic Approach

Initial imaging should include:

• Ultrasound as the first-line modality for initial detection and characterization 5
• CT abdomen and pelvis with IV contrast for definitive staging and surgical planning 1, 7
• MRI is recommended for staging the abdominal primary tumor and provides superior soft tissue characterization 5

Key imaging features of neuroblastoma:

• Heterogeneous mass with irregular capsule and visible calcifications (present in 85-90% of cases) 3
• Crosses the midline and encases vessels rather than displacing them 5, 6
• Retroperitoneal location most common 4, 6

Critical Diagnostic Steps

• Tissue sampling is mandatory for definitive diagnosis through either surgical resection or core biopsy 1
• Urinary catecholamine metabolites (vanillylmandelic acid and homovanillic acid) are elevated in 90% of cases and support the diagnosis 1
• Complete blood count, lactate dehydrogenase, and ferritin should be obtained as prognostic markers 1

Age-Related Considerations

• Age at diagnosis is the best predictor of survival, with infants under 1 year having nearly 100% cure rates 5
• While neuroblastoma is primarily a pediatric malignancy, adult cases are extremely rare (1 in 10 million adults/year) and have worse prognosis 4