[18F]FDG uptake of axillary lymph nodes after COVID-19 vaccination in oncological PET/CT: frequency, intensity, and potential clinical impact

Eur Radiol. 2022 Jan;32(1):508-516. doi: 10.1007/s00330-021-08122-2. Epub 2021 Jun 22.


Objectives: To assess the frequency, intensity, and clinical impact of [18F]FDG-avidity of axillary lymph nodes after vaccination with COVID-19 vaccines BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna) in patients referred for oncological FDG PET/CT.

Methods: One hundred forty patients referred for FDG PET/CT during February and March 2021 after first or second vaccination with Pfizer-BioNTech or Moderna were retrospectively included. FDG-avidity of ipsilateral axillary lymph nodes was measured and compared. Assuming no knowledge of prior vaccination, metastatic risk was analyzed by two readers and the clinical impact was evaluated.

Results: FDG PET/CT showed FDG-avid lymph nodes ipsilateral to the vaccine injection in 75/140 (54%) patients with a mean SUVmax of 5.1 (range 2.0 - 17.3). FDG-avid lymph nodes were more frequent in patients vaccinated with Moderna than Pfizer-BioNTech (36/50 [72%] vs. 39/90 [43%] cases, p < 0.001). Metastatic risk of unilateral FDG-avid axillary lymph nodes was rated unlikely in 52/140 (37%), potential in 15/140 (11%), and likely in 8/140 (6%) cases. Clinical management was affected in 17/140 (12%) cases.

Conclusions: FDG-avid axillary lymph nodes are common after COVID-19 vaccination. The avidity of lymph nodes is more frequent in Moderna compared to that in Pfizer-BioNTech vaccines. To avoid relatively frequent clinical dilemmas, we recommend carefully taking the history for prior vaccination in patients undergoing FDG PET/CT and administering the vaccine contralateral to primary cancer.

Key points: • PET/CT showed FDG-avid axillary lymph nodes ipsilateral to the vaccine injection site in 54% of 140 oncological patients after COVID-19 vaccination. • FDG-avid lymphadenopathy was observed significantly more frequently in Moderna compared to patients receiving Pfizer-BioNTech-vaccines. • Patients should be screened for prior COVID-19 vaccination before undergoing PET/CT to enable individually tailored recommendations for clinical management.

Keywords: COVID-19 vaccines; Fluorodeoxyglucose F18; Lymph nodes; Positron-emission tomography.

MeSH terms

  • 2019-nCoV Vaccine mRNA-1273
  • BNT162 Vaccine
  • COVID-19 Vaccines*
  • COVID-19*
  • Fluorodeoxyglucose F18
  • Humans
  • Lymph Nodes / diagnostic imaging
  • Positron Emission Tomography Computed Tomography
  • Retrospective Studies
  • SARS-CoV-2
  • Vaccination


  • COVID-19 Vaccines
  • Fluorodeoxyglucose F18
  • 2019-nCoV Vaccine mRNA-1273
  • BNT162 Vaccine