What does

Understanding "Reactive" on Ultrasound

In ultrasound imaging, "reactive" typically refers to a physiological response to inflammation, infection, or other stimuli that causes changes in tissue appearance without necessarily indicating malignancy.

Reactive Lymph Nodes

• Reactive lymph nodes on ultrasound show specific characteristics that differentiate them from malignant nodes:

  • Diffuse, uniform cortical thickening (typically less than 5.4 mm) 1
  • Preserved fatty hilum 1
  • Oval or reniform (kidney-shaped) appearance 1
  • Normal to slightly increased vascularity 2

• Cortical thickness is a key distinguishing feature:

  • Benign reactive nodes average 5.1 mm ± 2.8 mm in cortical thickness
  • Malignant nodes average 8.9 mm ± 4.5 mm in cortical thickness 1
  • A cortical thickness ≥5.4 mm has 74% sensitivity and 69% specificity for malignancy 1

Causes of Reactive Changes

• Inflammatory processes:

  • Infection (bacterial, viral) 3
  • Autoimmune conditions 2
  • Post-vaccination responses (e.g., COVID-19 vaccine) 1
  • Trauma or tissue injury 4

• In lymphoma assessment, reactive changes may be seen in:

  • Bone marrow following chemotherapy or myeloid colony-stimulating factors 5
  • Spleen during treatment 5
  • Lymph nodes responding to therapy 5

Clinical Significance

• Reactive changes on ultrasound often represent a normal immune response rather than pathology 2
• In lymphoma assessment, diffuse uptake compatible with reactive changes from chemotherapy is considered part of normal response 5
• Distinguishing reactive from malignant changes:
  • Nodal morphology (uniform vs. focal lobulation) is highly predictive 1
  • Nodes with focal cortical lobulation have 123 times higher odds of malignancy compared to those with diffuse, uniform thickening 1

Monitoring Reactive Changes

• In lymphoma follow-up, reactive changes should be monitored but may not require immediate intervention 5
• If uncertain about the etiology of reactive changes:
  • Consider follow-up imaging in 4-12 weeks 1
  • Biopsy may be necessary if changes persist or worsen 5
  • Correlation with inflammatory markers (CRP, MMP-3) may be helpful 2, 3

Pitfalls and Caveats

• Reactive changes can sometimes mimic pathological conditions 1
• Timing matters - recent vaccination, infection, or treatment can cause temporary reactive changes 1
• Context is crucial - patient history and clinical presentation should always be considered when interpreting "reactive" findings 2
• In post-treatment assessment of lymphoma, residual uptake higher than normal marrow but reduced from baseline may represent reactive changes rather than residual disease 5