What are the potential causes and appropriate management for a 13-month-old child presenting with a lump in the stomach?

Abdominal Mass in a 13-Month-Old Infant

A palpable abdominal mass in a 13-month-old child requires urgent evaluation with ultrasound as the initial imaging modality to differentiate between benign and malignant causes, with the most common serious diagnoses being neuroblastoma, Wilms tumor, and intussusception. 1, 2

Immediate Clinical Assessment

Key Physical Examination Findings to Identify

• Palpate for mass characteristics: location (flank masses suggest renal origin like Wilms tumor; midline/paravertebral masses suggest neuroblastoma), size, mobility, and consistency 1
• Assess for signs of intestinal obstruction: abdominal distension, bilious vomiting, absence of bowel sounds, or bloody stools (suggesting intussusception) 3, 4
• Look for systemic signs: fever, weight loss, pallor, hypertension (can occur with Wilms tumor), or periorbital ecchymoses and proptosis (neuroblastoma metastases) 1
• Examine the lower back: inspect for cutaneous markers of spinal dysraphism (dimples, hair tufts, skin discoloration) that could indicate neurologic causes 5

Critical Red Flags Requiring Emergent Evaluation

• Bilious vomiting: suggests obstruction distal to the ampulla of Vater and requires immediate imaging to exclude malrotation with volvulus 3, 6
• Bloody stools with intermittent crampy pain and lethargy: classic triad for intussusception, though uncommon before 3 months, it occurs in this age group 3, 2
• Hemodynamic instability or peritoneal signs: may indicate perforation, volvulus, or tumor rupture requiring emergent surgical consultation 7

Initial Diagnostic Imaging Approach

First-Line Imaging: Abdominal Ultrasound

Ultrasound is the preferred initial imaging modality for evaluating an abdominal mass in infants because it avoids ionizing radiation, is widely available, does not require sedation, and allows dynamic assessment of the mass and surrounding structures. 2, 3

• For suspected solid organ masses: ultrasound can differentiate renal masses (Wilms tumor) from adrenal/retroperitoneal masses (neuroblastoma) and assess for hepatic involvement 3, 1
• For suspected intussusception: ultrasound demonstrates the classic "target sign" or "pseudokidney sign" and can guide therapeutic reduction 2, 4
• Doppler ultrasound: helps characterize vascular flow patterns to distinguish vascular anomalies from solid tumors 3

When to Obtain Plain Radiographs First

• If signs of bowel obstruction are present (distension, bilious vomiting, absence of stool): obtain abdominal radiograph to assess bowel gas pattern, looking for dilated loops, air-fluid levels, or absence of distal gas 3, 5
• Plain films are inadequate for characterizing solid masses and should not delay ultrasound evaluation 1

Differential Diagnosis by Age and Presentation

Most Common Malignant Abdominal Masses at 13 Months

1. Neuroblastoma: most common abdominal malignancy in this age group; typically presents as firm, irregular, fixed paravertebral or adrenal mass crossing midline 1
2. Wilms tumor: second most common; presents as smooth, unilateral flank mass that does not cross midline; peak incidence 2-5 years but can occur at 13 months 1
3. Hepatoblastoma: less common but important consideration; associated with elevated alpha-fetoprotein 3

Benign/Surgical Emergencies to Exclude

• Intussusception: intermittent colicky pain, "currant jelly" stools, palpable sausage-shaped mass in right upper quadrant 3, 2, 4
• Intestinal duplication cyst or mesenteric cyst: can present as palpable mass 4
• Hydronephrosis from ureteropelvic junction obstruction: presents as flank mass 1

Management Algorithm

If Ultrasound Confirms Solid Mass

1. Obtain urgent pediatric oncology and surgical consultation within 24 hours for biopsy planning and staging workup 1
2. Additional imaging: MRI with contrast is typically needed for surgical planning and to assess for metastases, though this should be coordinated with oncology 3
3. Laboratory workup: complete blood count, comprehensive metabolic panel, urinary catecholamines (for neuroblastoma), alpha-fetoprotein (for hepatoblastoma) 1

If Ultrasound Suggests Intussusception

• Proceed directly to therapeutic air or contrast enema reduction under fluoroscopic or ultrasound guidance if no signs of perforation 2, 4
• Surgical consultation should be obtained before attempted reduction in case of failure or perforation 4

If Ultrasound Shows Bowel Obstruction

• Obtain upper GI series if malrotation is suspected (though this is less common at 13 months than in neonates) 3, 4
• Surgical consultation for potential operative intervention 3

Common Pitfalls to Avoid

• Do not delay imaging for laboratory results in a child with a palpable abdominal mass, as timely diagnosis significantly impacts outcomes for malignancies 1
• Do not assume gastroenteritis in a child with vomiting and a palpable mass; always consider surgical and oncologic emergencies 8
• Do not start with CT scanning as the initial imaging modality; ultrasound provides excellent diagnostic information without radiation exposure in this age group 2
• Repeated examinations are valuable: children may appear playful between episodes of pain (as in intussusception), so serial assessments can reveal evolving pathology 8