What is the appropriate evaluation and work‑up for a 24‑year‑old with an enlarged inguinal lymph node?

Work-Up for Swollen Inguinal Lymph Node in a 24-Year-Old

Begin with high-frequency ultrasound (>10 MHz) as the first-line imaging modality, followed immediately by ultrasound-guided fine-needle aspiration (FNA) if the node appears abnormal, as this combination achieves 91.7% sensitivity and 98.2% specificity for detecting malignancy. 1

Initial Clinical Assessment

Document the following specific characteristics during physical examination:

• Node characteristics: Size (measure diameter in centimeters), consistency (soft vs. firm), mobility versus fixation to surrounding structures, and relationship to skin and Cooper ligaments 1, 2
• Laterality: Unilateral versus bilateral presentation—examine both groins even if only one side appears involved due to crossover lymphatic drainage 1
• Associated findings: Presence of edema in the penis, scrotum, or lower extremities 2
• Location specificity: Whether the mass is above or below the inguinal ligament, medial versus lateral positioning 1

Search for Primary Source

Perform a systematic examination of potential primary sites:

• Genital examination: Inspect the penis, scrotum, and perineum for lesions, ulcers, or masses that could represent penile squamous cell carcinoma 3, 2
• Lower extremity skin: Examine for melanoma, wounds, or signs of infection 2
• Digital rectal examination: Assess for anal lesions and perirectal nodal involvement 1
• Risk factor assessment: Document history of HPV infection, HIV status, tobacco use, poor hygiene, and presence of any penile lesions 1

Diagnostic Imaging Algorithm

First-Line: Ultrasound with FNA

• Order high-frequency ultrasound (>10 MHz) to differentiate between hernia, lymphadenopathy, testicular masses, and vascular abnormalities 1
• Simultaneously request ultrasound-guided FNA if the node is enlarged or has abnormal characteristics on ultrasound 1, 2
• The combined approach raises diagnostic yield for metastases larger than 2 mm and provides definitive tissue diagnosis 1

If FNA is Negative

• Proceed with excisional biopsy if the node has heterogeneous appearance or remains clinically suspicious, as 20-25% of clinically node-negative patients harbor occult metastases 1, 2
• Do not assume a negative FNA excludes malignancy in a persistently abnormal node 2

If FNA is Positive for Malignancy

• Immediately initiate disease-specific oncologic management based on the primary malignancy identified 2
• Order CT abdomen and pelvis with contrast to assess for additional pelvic or retroperitoneal lymphadenopathy and to evaluate the extent of disease 1, 2

Additional Imaging Considerations

• MRI pelvis: Consider when ultrasound findings are inconclusive or when detailed soft tissue characterization is needed 1
• PET/CT: Reserve for cases where inflammatory markers (ESR/CRP) are elevated and diagnosis remains uncertain after initial imaging, as it provides high accuracy for detecting occult malignancy 2

Critical Differential Diagnoses in a 24-Year-Old

Malignant Etiologies (Require Urgent Evaluation)

• Testicular cancer with metastatic spread: Check serum tumor markers (AFP, hCG, LDH) and perform testicular examination 1
• Melanoma of lower extremity: Examine skin thoroughly 2
• Lymphoma: Consider if constitutional symptoms (fever, night sweats, weight loss) are present 2
• Penile squamous cell carcinoma: Less common in this age group but must be excluded 3, 2

Infectious/Inflammatory Causes

• Reactive lymphadenopathy: From skin or soft tissue infection of lower extremity or perineum—30-50% of palpable inguinal nodes are inflammatory rather than malignant 1, 2
• Sexually transmitted infections: Consider in sexually active young adults 1

Common Pitfalls to Avoid

• Do not assume all palpable lymphadenopathy is malignant: Up to 50% of palpable inguinal nodes are enlarged due to inflammatory changes 1, 2
• Do not proceed to immediate surgical excision without FNA: This leads to unnecessary morbidity and delays diagnosis 2
• Do not overlook bilateral examination: Even when the mass appears unilateral, examine both groins due to crossover lymphatic drainage 1
• Do not skip the search for a primary lesion: Inguinal lymphadenopathy is rarely an isolated finding in malignancy 3, 1

Follow-Up Strategy

If Confirmed Reactive Lymphadenopathy

• Address the underlying infectious or inflammatory cause 2
• Monitor node size and characteristics clinically 2
• Reevaluate if swelling persists beyond several weeks of appropriate treatment, as this suggests chronic lymphedema or underlying malignancy requiring further workup 2, 4

If Malignancy is Confirmed

• Follow disease-specific oncologic protocols 2
• Consider repeat imaging to assess treatment response 2