What are the typical characteristics of palpable popliteal lymph nodes?

Popliteal Lymph Nodes: Clinical Characteristics

Palpable popliteal lymph nodes are abnormal and warrant immediate investigation, as normal popliteal nodes are typically not palpable on routine physical examination. 1

What You Should Feel (or Not Feel)

Normal State

• Popliteal lymph nodes are generally NOT palpable in healthy individuals 1
• When they become palpable, this indicates pathology requiring further workup 1

When Palpable, Consider These Characteristics

Size and Texture:

• Lymph nodes ≥1.5 cm in diameter are particularly concerning 2
• Firm, irregular, clustered, or fixed nodes suggest malignancy 2
• Mobile nodes may indicate reactive/inflammatory changes 2

Location and Number:

• Assess whether unilateral or bilateral 2
• Document the number of palpable masses 2
• Evaluate relationship to surrounding structures (skin, vessels) 2

Critical Differential Diagnosis

A palpable mass in the popliteal fossa is most commonly NOT a lymph node: 1

• Baker's Cyst: Comma-shaped, fluctuant mass causing swelling and tenderness behind the knee that worsens with exercise 1
• Popliteal Aneurysm: Any palpable popliteal mass with a prominent popliteal pulse requires urgent ultrasound to exclude this life-threatening condition 1

If truly a lymph node, consider:

• Metastatic melanoma or squamous cell carcinoma from the lower leg 1
• Reactive lymphadenopathy from chronic skin wounds or infections 1
• Rheumatoid arthritis (multiple nodes, larger size, lack of central fatty change on imaging) 3

Examination Technique

Optimal positioning: 1

• Position the patient prone for best access to the posterior knee region 1
• Perform both longitudinal and transverse palpation 1

What to document:

• Palpability, dimensions, mobility versus fixation 2
• Relationship to skin and other structures 2
• Presence of edema in the leg, which may indicate lymphatic obstruction 2

Key Clinical Pitfall

Never assume a palpable popliteal mass is simply a lymph node without imaging. Failure to exclude popliteal aneurysm can result in thrombosis and limb loss 1. All patients with a palpable popliteal mass require ultrasound examination 1.

When Popliteal Nodes Are Detected on Imaging

Lymphoscintigraphy findings:

• Popliteal sentinel nodes are detected in only 9-36% of patients with lower leg melanomas 4, 5
• Visualization of popliteal nodes during routine pedal lymphoscintigraphy for limb swelling indicates impaired lymphatic drainage 6
• Popliteal nodes are seen in 43.4% of patients with clinical lymphedema and abnormal lymphoscintigraphy 6

If popliteal sentinel nodes are identified on lymphoscintigraphy, biopsy should be performed, as micrometastases can occur in popliteal nodes even when inguinal nodes are negative 4.

Management Algorithm for Palpable Popliteal Masses

1. First step: Ultrasound to exclude popliteal aneurysm 1
2. If cystic and communicates with joint: Baker's cyst 1
3. If solid and concerning for lymph node:
   • Fine-needle aspiration for nodes <4 cm 2, 7
   • Excisional biopsy if FNA negative but clinical suspicion remains 7
   • Immediate surgical management if FNA positive for malignancy 7

Clinical context matters: Evaluation may be difficult if significant scarring is present in the popliteal region 1.