From the Guidelines
Radiologists can often differentiate between reactive and malignant lymph nodes on ultrasound and mammogram, though with limitations, and the most recent and highest quality study 1 suggests that a combination of ultrasonographic features such as size, shape, margin, echogenicity, and presence of central hilar structure or necrosis can help predict malignancy. When evaluating lymph nodes on ultrasound, benign reactive nodes typically maintain an oval or reniform shape with a preserved fatty hilum and thin, regular cortex, whereas malignant nodes tend to appear more rounded, with loss of the fatty hilum, irregular cortical thickening, abnormal blood flow patterns, and sometimes extracapsular extension. On mammogram, reactive nodes usually show a radiolucent center (fatty hilum) with a thin rim of density, while malignant nodes may appear denser, rounder, and lack the fatty hilum. However, these imaging findings have considerable overlap, and no single feature is perfectly reliable. Size alone is not a definitive indicator, as reactive nodes can enlarge significantly during infection or inflammation. Some key ultrasonographic features that can help predict malignancy include:
- A round shape
- Distinct margins
- Heterogeneous echogenicity
- Presence of a central necrosis sign Ultimately, while imaging provides valuable information for initial assessment, definitive diagnosis of malignancy in lymph nodes often requires tissue sampling through fine needle aspiration or biopsy, especially in patients with known or suspected cancer 1. It is essential to consider the clinical context and use a combination of imaging features and clinical suspicion to guide the decision for tissue sampling. In clinical practice, the use of ultrasound-guided fine needle aspiration or core biopsy of suspicious lymph nodes can help establish a definitive diagnosis and guide further management 1.
From the Research
Differentiation of Reactive and Malignant Lymph Nodes
- The differentiation between reactive and malignant lymph nodes using ultrasound or mammogram can be challenging due to overlapping sonographic features 2, 3, 4.
- Studies have shown that ultrasound-guided fine-needle aspiration (FNA) of indeterminate or suspicious axillary lymph nodes can provide a more definitive diagnosis than ultrasound alone 3.
- The sensitivity, specificity, and diagnostic accuracy of ultrasound-guided FNA in detecting metastatic lymph nodes have been reported to be 86.4%, 100%, and 79.0%, respectively 3.
- However, the accuracy of FNA cytology in distinguishing reactive lymphoid hyperplasia from malignant lymphoma has been reported to be around 97%, with occasional false negative or false positive results 5.
- Vascular patterns detected by color Doppler flow imaging (CDFI) can also be used to differentiate benign from malignant lymphadenopathy, with certain patterns being suspicious of malignancy 6.
- The use of ancillary techniques such as immunocytochemistry, in situ hybridization, and polymerase chain reaction (PCR) can contribute to the diagnosis of lymph node lesions, but may also yield occasional misleading results 5.
Limitations and Challenges
- The overlap of sonographic features between benign and malignant lymph nodes can lead to diagnostic errors 2, 3, 4.
- Small-sized metastases and preoperative neoadjuvant chemotherapy can affect the accuracy of ultrasound-guided FNA 3.
- Sampling error or misinterpretation of FNA cytology results can also occur 5.
- The diagnostic accuracy of vascular patterns detected by CDFI may vary depending on the examiner and the specific criteria used 6.