What is the differential diagnosis for a 2‑year‑old Somali girl with a 3‑ to 4‑day history of a rapidly enlarging, tender inguinal mass presumed to be a lymph node?

Differential Diagnosis of Inguinal Mass in a 2-Year-Old Somali Girl

Primary Diagnostic Consideration

In a 2-year-old child presenting with a rapidly enlarging inguinal mass over 3–4 days, the most likely diagnosis is reactive lymphadenitis secondary to a local infection of the lower extremity, perineum, or genital region. 1

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Systematic Approach to Differential Diagnosis

Infectious/Inflammatory Causes (Most Common in This Age Group)

• Reactive lymphadenitis from local infection – Inspect the ipsilateral lower extremity for cuts, abrasions, insect bites, cellulitis, or fungal infection between the toes; examine the perineal, genital, and perianal regions for lesions, trauma, or dermatologic conditions. 1

• Viral lymphadenitis – A preceding viral prodrome or minor superficial infection can explain tender, mobile inguinal nodes without requiring antimicrobial therapy. 1

• Bacterial lymphadenitis – Staphylococcus or Streptococcus species from skin breaks can cause acute, tender, unilateral inguinal adenopathy. 1

• Sexually transmitted infections (STIs) – Although extremely rare in pre-pubertal children, HSV or syphilis should be considered only if genital lesions, ulcers, or concerning social history are present. 1 Lymphogranuloma venereum (LGV) is relevant only in sexually active adolescents with tender unilateral inguinal lymphadenopathy and is treated with doxycycline 100 mg orally twice daily for 21 days. 2, 1

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Non-Infectious Masses Mimicking Lymphadenopathy

• Inguinal hernia – The most common "mass" in the inguinal canal in children; however, irreducible masses should always receive appropriate preoperative diagnosis to exclude other pathologies. 3, 4

• Cystic lymphangioma – A soft, partly reducible groin mass can represent a cystic lymphangioma within the inguinal canal. 5

• Epidermal inclusion cyst – An irreducible groin mass may prove to be an inguinal canal epidermal inclusion cyst. 5

• Incarcerated ovarian cyst – In females, a painful groin swelling can represent an incarcerated hemorrhagic ovarian cyst. 5

• Lipoma or myopericytoma – Rare mesenchymal soft tissue tumors can present as inguinal masses; myopericytoma is typically painless but can cause dull aching pain. 6

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Malignant Etiologies (Rare but Critical to Exclude)

• Neuroblastoma metastasis – An irreducible inguinal mass in a young child can represent metastatic neuroblastoma to the groin. 5

• Lymphoma – Should be considered if systemic "B" symptoms (fever, night sweats, weight loss) are present, though uncommon in this age group. 7, 2

• Soft-tissue sarcoma – Retroperitoneal or lower extremity sarcomas can present as groin masses. 7, 8

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Diagnostic Algorithm

Step 1: Clinical Examination

• Document node size (short-axis and maximal dimension), number, mobility versus fixation, and associated edema or skin changes. 7

• Perform a systematic examination of the ipsilateral lower extremity, perineum, genitalia, and perianal region for infection sources or primary lesions. 1

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Step 2: Initial Management Based on Clinical Findings

• If small, mobile, tender nodes without systemic symptoms or overlying skin changes are present – Schedule clinical reassessment in 2–4 weeks; nodes should decrease in size within 4–6 weeks. 1

• If a clear viral cause or minor superficial infection is identified – Observation without antimicrobial therapy is appropriate. 1

• If nodes are ≥3 cm, fixed, non-tender, or associated with systemic symptoms – Proceed immediately to imaging and tissue diagnosis. 7, 2

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Step 3: Imaging When Indicated

• Obtain ultrasound of the groin – First-line imaging in children to differentiate lymph nodes from other masses (hernia, cyst, solid tumor). 3, 5

• Consider CT abdomen and pelvis with IV contrast – If malignancy is suspected, to assess for deeper pelvic, retroperitoneal involvement, or a primary tumor. 7, 2

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Step 4: Tissue Diagnosis

• Fine-needle aspiration (FNA) – Demonstrates 91.7% sensitivity and 98.2% specificity for malignancy in adults; however, when malignancy or granulomatous disease is suspected in children, excisional biopsy is preferred over FNA. 1

• Excisional biopsy – Recommended for persistent, enlarging, or suspicious nodes to exclude malignancy or atypical infection. 7, 1

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Critical Pitfalls to Avoid

• Do not assume all inguinal masses in children are hernias – Irreducible masses require appropriate preoperative diagnosis to exclude neoplasms or other rare lesions. 3, 4

• Do not delay tissue diagnosis for persistent or enlarging nodes – Lack of improvement within 4–6 weeks should prompt reconsideration of diagnosis or escalation of care. 1

• Do not overlook a thorough skin and perineal examination – Most pediatric inguinal lymphadenitis is reactive to local infection, which can be identified on careful inspection. 1

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Summary of Most Likely Diagnoses in This Case

1. Reactive lymphadenitis from local infection (most common). 1
2. Inguinal hernia (most common groin mass overall). 3, 4
3. Cystic lymphangioma or epidermal inclusion cyst (rare but reported). 5
4. Neuroblastoma metastasis or lymphoma (rare but must be excluded if nodes persist or systemic symptoms develop). 5, 7