What size is considered enlarged for a lymph node or mass?

Lymph Node Size Thresholds for Defining Enlargement

A lymph node is considered enlarged when its short-axis diameter exceeds 10 mm, with specific size thresholds varying by anatomical location. 1

Standardized Size Criteria by Location

General Lymph Node Size Thresholds:

• Mediastinal/Hilar lymph nodes: >10 mm in short axis 1
• Suspicious for pathology: >15 mm in short axis 1, 2
• Measurable node criteria: Long diameter >1.5 cm 1

Specific Anatomical Locations:

• Upper abdominal lymph nodes (vary by precise location) 3:
  • Retrocrural space: >6 mm
  • Paracardiac: >8 mm
  • Gastrohepatic ligament: >8 mm
  • Upper paraaortic: >9 mm
  • Portacaval space: >10 mm
  • Porta hepatis: >7 mm
  • Lower paraaortic: >11 mm

Clinical Significance and Measurement Techniques

Measurement Method:

• For nodal assessment: Measure the short axis diameter 1
• For response criteria: Use the longest diameter for non-nodal lesions and short axis for nodal lesions 1

Diagnostic Implications:

• Nodes >10 mm in short axis are considered abnormal, but this alone is not definitive for malignancy 1, 4
• Nodes >15 mm are more likely to be pathologic 1, 2
• Nodes >25 mm are almost always pathologic 1

Important Caveats:

• Size alone is an unreliable predictor of metastatic involvement 4
  • 44% of metastatic lymph nodes are <10 mm in diameter
  • 77% of patients without metastatic involvement have at least one lymph node >10 mm
• Normal-sized nodes may still contain malignancy, especially in lymphoma 1
• PET-CT is preferred for assessing metabolic activity in normal-sized nodes 1, 2

Specific Disease Considerations

Lymphoma:

• The Lugano Classification defines measurable nodes as those with long diameter >1.5 cm 1
• For response assessment, nodes with long axis 1.1-1.5 cm and short axis >1.0 cm before treatment must decrease to ≤1.0 cm in short axis after treatment to qualify as complete response 1

Solid Tumors (RECIL 2017 Criteria):

• Target lesions: Lymph nodes with long diameter ≥15 mm 1
• Nodes 10-14 mm are considered abnormal but not target lesions 1
• Nodes <10 mm are considered normal 1

When to Refer for Further Evaluation

• Lymph nodes >15 mm in short axis warrant specialist referral 1, 2
• Consider additional factors beyond size:
  • Distribution pattern
  • Internal characteristics (calcification, necrosis)
  • Clinical context (known malignancy, symptoms)
  • FDG avidity on PET-CT if available 1, 2

Remember that while size thresholds are important guidelines, they should be interpreted in clinical context, as size alone has limitations in determining malignant involvement.