How do I order a high‑frequency (10‑15 MHz) linear‑array ultrasound of the inguinal and femoral region for a patient with palpable groin lymphadenopathy or suspected metastatic inguinal nodes?

How to Order Ultrasound for Groin Lymph Nodes

Order a high-frequency ultrasound (10-15 MHz linear array transducer) of the inguinal and femoral regions, specifying bilateral examination even if unilateral disease is suspected, with documentation of node size, cortical thickness, hilum presence, L/T ratio, and vascular pattern. 1, 2

Specific Ordering Instructions

Technical Specifications Required

• Use high-frequency linear array transducer (10-15 MHz) for optimal resolution of superficial lymph node architecture 3, 2
• Specify examination of both inguinal and femoral regions bilaterally, as crossover lymphatic drainage occurs even with unilateral presentation 1
• Request gray-scale imaging with color-power Doppler evaluation of nodal vascularity 2

Critical Features to Document in Order

The radiologist must assess and report the following parameters:

Nodal Morphology:

• Longitudinal/transverse (L/T) diameter ratio (L/T <2 suggests malignancy with 81% sensitivity) 2
• Presence or absence of echogenic fatty hilum (absent hilum has 95% specificity for metastasis) 2
• Cortical appearance: thickness, homogeneity, and whether eccentric (eccentric cortex has 96% specificity for malignancy) 2
• Node size and number in each anatomic zone 1, 4

Vascular Pattern:

• Characterization of blood flow distribution (peripheral vs. hilar) 2
• Assessment of vascular architecture disruption 2

Clinical Context to Provide

Essential History for Radiologist

Include on the requisition:

• Primary malignancy risk factors: penile lesions, melanoma, anal cancer, vulvar cancer, lower extremity sarcoma, or gynecologic malignancy 1, 5
• HPV status, HIV status, and history of sexually transmitted infections 1
• Previous groin surgery, radiation, or chemotherapy 1
• Whether nodes are palpable on examination and their characteristics (size, mobility, consistency) 6, 7

Specify Clinical Question

State whether ultrasound is for:

• Initial staging of known malignancy with clinically negative groins 6
• Evaluation of palpable lymphadenopathy to guide fine-needle aspiration 6, 5
• Surveillance after sentinel node biopsy or primary tumor treatment 8

When to Add Ultrasound-Guided FNA to Order

Simultaneously order ultrasound-guided fine-needle aspiration if:

• Nodes are palpable and >1.5 cm 5, 7
• Ultrasound shows any suspicious features (L/T <2, absent hilum, eccentric cortex) 2
• Patient has known primary malignancy with enlarged inguinal nodes 6, 5

The combination of ultrasound with FNA increases diagnostic yield for metastases >2 mm in diameter and achieves 91.7% sensitivity and 98.2% specificity for malignancy 6, 5

Critical Pitfalls to Avoid

Do not assume palpable nodes are malignant without imaging confirmation - 30-50% of palpable inguinal lymphadenopathy represents inflammatory changes rather than metastatic disease 6, 1

Do not order unilateral examination only - bilateral assessment is mandatory due to crossover lymphatic drainage patterns, even when clinical disease appears unilateral 1

Do not rely on ultrasound alone for definitive exclusion of metastasis - sensitivity is 76-87% for detecting metastatic disease, so negative ultrasound in high-risk patients requires either FNA confirmation or close surveillance 4, 8

Recognize that structural alterations (moderate cortical thickening, slight loss of hilar curvature) may be benign variants - these findings alone without other suspicious features do not mandate biopsy, as they frequently remain stable without progression to malignancy 9

Follow-Up Imaging Protocol

For surveillance after negative initial staging:

• Repeat ultrasound every 3 months for the first 2 years 5
• Ultrasound-guided FNA detects 80% of nonpalpable recurrences during follow-up 8
• Any enlarging nodes or new suspicious features warrant immediate FNA 5, 8