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

Neuroblastoma is the Most Likely Diagnosis

In a child presenting with a painless abdominal mass, neuroblastoma is the most likely diagnosis, particularly when considering the classic presentation pattern and epidemiologic data showing it is one of the three most common pediatric abdominal malignancies. 1, 2

Age-Specific Differential Diagnosis

The age of the child is critical for narrowing the differential:

• Neuroblastoma typically presents in the first decade of life, most commonly in infants and young children under 5 years, arising from sympathetic nervous tissue anywhere in the body but most often developing in the abdomen 3, 2
• Wilms tumor also presents in early childhood, typically between ages 2-5 years, and represents the most common renal malignancy in children 4, 5, 2
• Hepatoblastoma occurs predominantly in children under 4 years of age, with peak incidence in infancy 6, 2

Key Clinical Features to Distinguish Diagnoses

Neuroblastoma-Specific Findings:

• Hypertension is a classic associated finding due to catecholamine excess or renal artery compression 1
• Additional supportive features include fever, weight loss, irritability, bone pain, periorbital ecchymosis ("raccoon eyes"), or opsoclonus-myoclonus-ataxia syndrome 1, 6
• Elevated urinary catecholamines (VMA and HVA) are present in the majority of patients 1
• Metastatic disease to bone or bone marrow is more characteristic of neuroblastoma than other pediatric abdominal tumors 4

Wilms Tumor-Specific Findings:

• Hypertension is less characteristic compared to neuroblastoma 1
• May present with renal signs including hematuria and abdominal pain 3
• Ultrasound confirms renal origin of the mass 4

Hepatoblastoma-Specific Findings:

• Hypertension is NOT a characteristic feature 1
• Elevated AFP levels are characteristic 4
• Hepatic mass on ultrasound 4

Diagnostic Workup Algorithm

Initial Laboratory Studies:

• Urinary catecholamines (VMA and HVA) - essential for neuroblastoma diagnosis 1
• Complete blood count with differential 1
• Comprehensive metabolic panel 1
• AFP levels if hepatoblastoma is suspected 4

Initial Imaging:

• Abdominal ultrasound is the optimal first-line imaging modality - widely available, lacks ionizing radiation, can be performed without sedation 4, 7, 5
• Ultrasound has excellent diagnostic performance: for neuroblastoma (sensitivity 83.3%, specificity 98.0%), for Wilms tumor (sensitivity 100%, specificity 90.6%), and for hepatoblastoma (sensitivity and specificity both 100%) 5

Advanced Imaging:

• CT or MRI to characterize the mass, assess for renal artery compression, and stage disease extent 1, 2
• MIBG scan may be helpful for neuroblastoma diagnosis, particularly in opsoclonus-myoclonus-ataxia syndrome 6

Tissue Diagnosis:

• Multiple core biopsies or surgical resection required for definitive diagnosis of neuroblastoma, with adequate tissue for histologic and molecular evaluation (MYCN amplification, ALK mutations) 1
• Fine-needle aspiration is NOT recommended for neuroblastoma diagnosis 1

Critical Pitfalls to Avoid

• Do not dismiss the absence of hypertension - while characteristic of neuroblastoma, it is not universally present 1
• Do not rely solely on imaging - tissue diagnosis with molecular characterization is essential for neuroblastoma management 1
• Consider genetic predisposition syndromes - if Beckwith-Wiedemann syndrome features are identified (macroglossia, omphalocele/umbilical hernia, hemihyperplasia), implement standardized tumor surveillance protocols 1, 8