How should an infant with a newly discovered intra‑abdominal mass be evaluated and managed?

Evaluation and Management of Intra-Abdominal Mass in an Infant

Ultrasonography is the optimal initial imaging modality for any infant with a newly discovered intra-abdominal mass, and should be performed immediately to characterize the lesion and guide further management. 1

Initial Diagnostic Approach

Immediate Imaging

• Perform abdominal ultrasonography first in all infants with a palpable or suspected intra-abdominal mass—it provides high sensitivity without ionizing radiation or sedation, making it ideal for this age group 2, 1
• Doppler ultrasonography should be included to assess vascular characteristics and flow patterns, which helps differentiate between vascular tumors (infantile hemangiomas), malformations, and solid masses 2
• The ultrasound examination must evaluate mass location (retroperitoneal vs. intraperitoneal), size, echogenicity (solid, cystic, or mixed), and relationship to surrounding organs 1, 3

Critical Clinical Features to Assess

• Age at presentation is the single most important clinical factor—neuroblastoma peaks in infancy, Wilms' tumor in ages 2-5 years, hepatoblastoma in children under 3 years, and lymphomas in older children 3, 4
• Document associated symptoms: abdominal distension, pain, vomiting, constipation, or painless lymphadenopathy (suggesting lymphoma) 1, 3
• Examine for cutaneous findings: ≥5 cutaneous infantile hemangiomas mandate screening for hepatic hemangiomas 2
• Palpate for mass characteristics: location (upper vs. lower abdomen, crosses midline), consistency, mobility, and tenderness 3, 4

Essential Laboratory Studies

• Obtain serum alpha-fetoprotein (AFP) immediately using age-specific reference ranges—elevated AFP suggests hepatoblastoma or germ cell tumors 1, 3
• Complete blood count with differential to assess for anemia, thrombocytopenia, or leukocytosis 1
• Urinary catecholamines (vanillylmandelic acid and homovanillic acid) if neuroblastoma is suspected based on imaging 3, 4

Advanced Imaging Indications

When to Proceed to MRI

• MRI without and with IV contrast is indicated when ultrasound findings are indeterminate, when characterizing complex masses, or when associated structural abnormalities are suspected 1, 2
• MRI provides superior soft-tissue characterization for retroperitoneal masses, hepatic lesions, and evaluation of vascular invasion or spinal extension 1, 4
• For infants under 6 months, MRI may require sedation; however, feed-and-swaddle techniques can often achieve adequate imaging without anesthesia 2

Role of CT Imaging

• CT with IV contrast should be reserved for situations where MRI is unavailable, contraindicated, or when rapid imaging is required in an unstable patient 1
• CT exposes infants to ionizing radiation and should be avoided when ultrasonography or MRI can provide equivalent diagnostic information 2, 1
• Chest CT is indicated for staging when malignancy is confirmed, particularly for neuroblastoma, Wilms' tumor, or lymphoma 1

Differential Diagnosis by Age and Location

Most Common Malignant Masses in Infancy

• Neuroblastoma (most common malignant abdominal mass in infants)—typically retroperitoneal, crosses midline, calcifications on imaging, elevated urinary catecholamines 3, 4
• Wilms' tumor (nephroblastoma)—intrarenal mass, does not cross midline, peak age 2-5 years but can occur in infancy 1, 3
• Hepatoblastoma—right upper quadrant mass, elevated AFP, most common in children under 3 years 1, 3

Benign Cystic Lesions

• Mesenteric cysts and cystic lymphangiomas present with abdominal pain, distension, or palpable mass; ultrasound shows multiloculated cystic lesions 5, 6
• Hepatic cysts (including hepatobiliary cystadenoma and benign hamartoma) appear as well-defined cystic structures on ultrasound 5
• Even asymptomatic benign cysts require surgical excision due to risk of volvulus, intestinal gangrene, or progressive growth 7, 6

Infantile Hemangiomas

• Multifocal or diffuse infantile hepatic hemangiomas occur in infants with ≥5 cutaneous hemangiomas; Doppler ultrasound is the screening modality of choice 2
• Hepatic hemangiomas appear as hypoechoic or mixed-echogenicity lesions with high-flow vascular characteristics on Doppler 2

Management Principles

Urgent Referral Criteria

• All infants with suspected malignant abdominal masses must be referred immediately to a specialized pediatric oncology center with multidisciplinary expertise 1
• Symptomatic masses causing pain, vomiting, or signs of intestinal obstruction require urgent surgical consultation 5, 6
• Large masses (>4-5 cm) or those with imaging features suggesting malignancy warrant expedited evaluation within 24-48 hours 1, 3

Tissue Diagnosis

• Obtain tissue diagnosis before initiating definitive therapy whenever feasible—this may be via percutaneous biopsy, bone marrow aspirate (for suspected lymphoma or metastatic neuroblastoma), or surgical excision 1, 3
• In critically ill infants with oncologic emergencies (tumor lysis syndrome, respiratory compromise from mass effect), treatment may need to begin before definitive histologic diagnosis 1

Surgical Considerations

• Complete surgical excision is curative for benign cystic lesions and provides definitive histologic diagnosis 5, 6
• For malignant tumors, surgical approach depends on tumor type, stage, and resectability—many require neoadjuvant chemotherapy before attempted resection 4
• Nephron-sparing surgery should be considered for Wilms' tumor in syndromic patients (e.g., WAGR syndrome, Denys-Drash syndrome) 1

Critical Pitfalls to Avoid

• Never delay imaging in an infant with a palpable abdominal mass—early diagnosis facilitates treatment and prevents catastrophic complications such as volvulus or tumor rupture 6, 4
• Do not assume benign etiology based on clinical presentation alone; even asymptomatic masses can represent malignancy or develop life-threatening complications 7, 6
• Avoid CT as first-line imaging in stable infants—ultrasonography provides excellent diagnostic information without radiation exposure 2, 1
• Do not obtain MRI without first performing ultrasonography unless there is a specific indication for immediate advanced imaging 2
• Never initiate empiric chemotherapy without tissue diagnosis except in true oncologic emergencies where delay would be life-threatening 1