Benign Lymph Node Enlargement: Etiology, Imaging Characteristics, and Evaluation Criteria

Etiology

Infectious processes such as pneumonia and other thoracic infections commonly produce mediastinal and hilar lymphadenopathy with short‑axis diameters exceeding 1 cm in both children and adults. (American College of Radiology) 1
Congestive heart failure in various clinical phases is associated with enlarged mediastinal lymph nodes larger than 2 cm in short axis. (American College of Radiology) 1
Interstitial lung diseases—including usual interstitial pneumonia, nonspecific interstitial pneumonia, respiratory bronchiolitis, cryptogenic organizing pneumonia, and desquamative interstitial pneumonia—frequently present with mediastinal and hilar lymphadenopathy. (American College of Radiology) 1
The extent of lymphadenopathy in interstitial lung disease correlates with overall disease severity, serving as an imaging marker of progression. (American College of Radiology) 1
Accessory breast tissue and benign lesions arising within it may manifest as palpable axillary masses that mimic lymphadenopathy. (American College of Radiology) 2
Implant‑related reactions to silicone or polyurethane materials can induce reactive lymph node enlargement, particularly when implant rupture occurs. (Journal of Clinical Oncology) 3

Benign lymph nodes typically display smooth, well‑defined borders on cross‑sectional imaging. (American College of Radiology) 1
They show uniform, homogeneous attenuation without necrotic or cystic areas. (American College of Radiology) 1
A central fatty hilum is usually preserved, aiding differentiation from malignant nodes. (American College of Radiology) 1
The short‑axis diameter is generally less than 15 mm; nodes exceeding this threshold warrant closer scrutiny. (American College of Radiology) 1

When a lymph node measures greater than 15 mm in short axis, loses its fatty hilum, or exhibits irregular, spiculated borders, further diagnostic work‑up (advanced imaging or tissue biopsy) is recommended regardless of potential benign explanations such as recent vaccination. (American College of Radiology) 1
Awareness of the pitfall of attributing enlargement solely to benign causes (e.g., recent mRNA COVID‑19 vaccination) is essential, as missed malignancy can delay treatment and worsen outcomes. (American College of Radiology) 1

Homogeneous echogenicity without central necrosis on ultrasound suggests a benign etiology for a lymph node measuring approximately 2.3 cm. 4

When none of the four malignant ultrasound features (round shape, distinct margins, heterogeneous echogenicity, central necrosis) are present, the likelihood that a 2.3 cm lymph node is benign increases to about 96 %. 4