From the Guidelines
Reactive lymphadenopathy typically involves multiple lymph nodes under 1.5 cm in diameter, while malignant lymphadenopathy often involves nodes larger than 2 cm. The distinction between reactive and malignant lymphadenopathy is crucial for determining the appropriate course of treatment and management. According to the study by Evison et al, cited in 1, lymph node size is a strong predictor of etiology, with nodes 15 mm or less in short axis typically being reactive, and those greater than 25 mm being pathologic.
Key Characteristics of Reactive and Malignant Lymphadenopathy
- Reactive lymphadenopathy:
- Typically involves multiple lymph nodes
- Nodes are usually under 1.5 cm in diameter
- Nodes are tender, mobile, and soft
- Distribution pattern is typically in the expected drainage area of an infection
- Malignant lymphadenopathy:
- Often involves nodes larger than 2 cm
- Nodes are frequently firm or hard, fixed to surrounding tissues, and painless
- Distribution pattern may be unusual or widespread
Importance of Lymph Node Size and Distribution
The size and distribution of lymph nodes are critical factors in determining the likelihood of malignancy. As noted in 1, a short-axis size threshold of 15 mm can guide the decision process, with nodes larger than this threshold warranting further investigation. Additionally, the presence of pulmonary findings and clinical history can also influence management decisions.
Clinical Implications
In clinical practice, it is essential to consider the size and distribution of lymph nodes, as well as other factors such as clinical history and pulmonary findings, when evaluating patients with lymphadenopathy. By doing so, healthcare providers can make informed decisions about the need for further testing, treatment, and management, ultimately improving patient outcomes. As stated in 1, a widely accepted definition of normal-sized mediastinal lymph nodes is a short-axis diameter of < 1 cm on a transverse CT scan image, highlighting the importance of accurate imaging and measurement in diagnosing and managing lymphadenopathy.
From the Research
Lymph Node Characteristics
- The size of lymph nodes in reactive lymphadenopathy is typically smaller, with a longest diameter of 13.5 mm +/- 6.0, whereas in malignant lymphadenopathy, the size is larger, with a longest diameter of 19.2 mm +/- 8.8 for nodal metastases and 23.2 mm +/- 10.5 for malignant lymphomas 2.
- The shape of lymph nodes on ultrasonography (US) can also be used to differentiate between reactive and malignant lymphadenopathy, with flat shapes more commonly seen in reactive lymphadenopathy and round shapes more commonly seen in malignant lymphadenopathy 3.
Diagnostic Criteria
- A lymph node size of ≥19.5 mm at an axial section on computed tomography (CT) image can be used as a cut-off value to differentiate malignant lymphadenopathy from other pathologies, offering 90.9% sensitivity and 87.5% specificity 3.
- Color Doppler US findings of intranodal blood vessels, such as focal perfusion defects, aberrant course of central vessels, displacement of intranodal vessels, and subcapsular vessels, can also be used to differentiate between reactive and malignant lymphadenopathy, with a specificity of 77% and a sensitivity of 96% 2.
- Ancillary studies, such as immunocytochemistry, in situ hybridisation, and polymerase chain reaction (PCR), can be applied to cytological samples and contribute to the diagnosis of lymphadenopathy, although occasional misleading results can occur 4.
Clinical Correlation
- Older age and higher levels of lactate dehydrogenase (LDH), soluble interleukin-2 receptor (sIL-2R), and maximum standardized uptake value (SUVmax) are more associated with lymphoproliferative disorders (LPD) than reactive lymph node hyperplasia (RLH) in patients with rheumatoid arthritis 5.
- Fine needle aspiration (FNA) cytology can accurately distinguish reactive lymphoid hyperplasia from malignant lymphoma in 97% of cases, although occasional wrong diagnoses can occur due to sampling error or misinterpretation 4.