In a 2‑year‑old girl with a large femoral mass, how should the femoral (inguinal) lymph node be assessed and managed?

Assessment and Management of Femoral Lymph Node in a 2-Year-Old Girl with Large Femoral Mass

In a 2-year-old child presenting with a large femoral mass, immediate ultrasound evaluation with fine-needle aspiration biopsy is the first-line diagnostic approach, as preserved fatty hilum on imaging significantly reduces malignancy probability, but tissue diagnosis is essential given that up to 25% of clinically negative lymph nodes harbor micrometastases. 1

Initial Diagnostic Workup

Clinical Examination Priorities

• Assess mass characteristics: size, consistency, mobility, relationship to femoral vessels, and presence of overlying skin changes 2
• Evaluate for systemic signs: fever, weight loss, night sweats suggesting lymphoma or infection 1
• Examine for primary tumor sites: skin lesions, extremity masses, or other lymphadenopathy that could indicate metastatic disease 3

First-Line Imaging

• Ultrasound is the initial imaging modality of choice to evaluate lymph node morphology, presence of fatty hilum, vascularity pattern, and relationship to femoral vessels 1
• A preserved fatty hilum is the single most important benign feature, with sensitivity 86-93% and specificity 96-100% for excluding metastatic involvement 1
• Hypervascularity alone is non-specific, as reactive lymphadenopathy from infection commonly demonstrates increased blood flow 1

Normative Size Data for Pediatric Inguinal Nodes

• Normal inguinal lymph nodes in children aged 0-17 years have mean maximum short-axis diameters ranging from 6.33-8.68 mm for superficial nodes and 3.62-5.83 mm for deep nodes 4
• Lymph nodes >15 mm short axis or with suspicious morphology warrant further investigation 5
• Normal pediatric inguinal nodes are typically multiple (mean 13.35 superficial nodes per patient), contain fat (86.6%), and are oval-shaped (99.2%) 4

Tissue Diagnosis Strategy

Biopsy Approach

• Ultrasound-guided fine-needle aspiration biopsy (US-FNAB) is recommended as the initial diagnostic procedure, with sensitivity 80-93% and specificity approaching 100% for detecting malignancy 1
• Core needle biopsy under imaging guidance is the next step if US-FNAB is non-diagnostic 1
• Excisional biopsy should only be performed at a specialized center by a surgeon who will perform definitive resection if malignancy is confirmed 1

Critical Laboratory Studies

• Complete blood count with differential to evaluate for leukemia or lymphoma 6
• Lactate dehydrogenase (LDH): elevated levels suggest lymphoma rather than solid tumor metastasis 6
• Consider tuberculin skin test or interferon-gamma release assay if tuberculous lymphadenitis is clinically suspected based on exposure history or endemic area 6

Differential Diagnosis Considerations

Malignant Etiologies

• Rhabdomyosarcoma: most common soft tissue sarcoma in children, with 24% having regional lymph node involvement at diagnosis in extremity cases 3
• Lymphoma: characterized by rapid onset, elevated LDH, and often multiple sites of lymphadenopathy 6, 1
• Metastatic disease: from occult primary tumors including neuroblastoma or other pediatric malignancies 3

Benign Etiologies

• Reactive lymphadenopathy: from lower extremity infection or inflammation, typically with preserved fatty hilum and hypervascularity 1
• Infectious causes: bacterial lymphadenitis, cat-scratch disease, or atypical mycobacterial infection 1

Advanced Imaging if Malignancy Suspected

Cross-Sectional Imaging

• CT pelvis with IV contrast if malignancy is confirmed on biopsy, to evaluate extent of disease and relationship to femoral vessels 6
• MRI pelvis and thigh for local staging if sarcoma is diagnosed, providing superior soft tissue characterization 1
• CT chest/abdomen/pelvis for metastatic evaluation if malignancy is confirmed 1

Functional Imaging

• FDG-PET/CT from skull base to mid-thigh for comprehensive staging if lymphoma is confirmed or aggressive histology is suspected 6, 1
• PET/CT has limited specificity for thymic masses and should not be used for routine assessment, but is valuable for lymphoma staging 6

Management Based on Diagnosis

If Reactive/Benign

• Observation and monitoring is the standard approach for reactive lymphadenopathy 1
• Trial of antibiotics may help differentiate reactive from malignant causes if infection is suspected 1
• Follow-up ultrasound in 4-6 weeks to document resolution or stability 1

If Malignant

• Immediate referral to specialized pediatric oncology center is mandatory 1
• For rhabdomyosarcoma of extremity: aggressive identification and treatment of regional lymph nodes is necessary, as regional involvement occurs in 24% of cases 3
• In-transit lymph node evaluation (popliteal for lower extremity) should be performed, as in-transit failures are as common as proximal nodal failures in distal extremity tumors 3
• Radiotherapy to involved nodal sites reduces in-transit failure rates from 15% to 0% when combined with appropriate lymph node sampling 3

Critical Pitfalls to Avoid

• Never assume benignity based solely on age: up to 25% of clinically negative lymph nodes harbor micrometastases, and delaying tissue diagnosis can lead to relapses that are rarely amenable to successful secondary treatment 1
• Do not administer corticosteroids before obtaining tissue diagnosis, as they can mask histologic features of lymphoma or malignancy 6
• Avoid relying on PET/CT alone for assessment, as it has limited specificity and reactive processes can show hypermetabolism 6
• Do not perform excisional biopsy at non-specialized centers, as inappropriate surgical approach can compromise subsequent definitive treatment 1
• Ensure adequate lymph node staging in extremity sarcomas, as incomplete regional evaluation is associated with higher failure rates 3