ABSTRACT
Background COVID-19 vaccination-related axillary lymphadenopathy has become an important problem in cancer imaging. Data is needed to update or support imaging guidelines for conducting appropriate follow-up. Purpose To investigate the prevalence, predisposing factors, and MRI characteristics of COVID-19 vaccination-related axillary lymphadenopathy. Materials and Methods Prospectively collected pre-vaccination and post-vaccination chest MRI scans were secondarily analyzed. Participants who underwent two doses of Pfizer-BioNtech or Moderna COVID-19 vaccine and chest MRI from June to October 2021 were included. Enlarged axillary lymph nodes were identified on post-vaccination MRI comparing with pre-vaccination MRI. Lymph node diameters, signal intensity on T2-weighted images (T2WIs) and apparent diffusion coefficient (ADC) of the largest enlarged lymph node were measured. These values were compared between pre-vaccination and post-vaccination MRI with the Wilcoxon signed-rank test. Results We evaluated 433 participants (mean age ± standard deviation, 65 years ± 11 years), 300 males and 133 females. The prevalence of axillary lymphadenopathy in participants 1-14 days after vaccination was 65% (30/46). Participants with lymphadenopathy were younger than those without lymphadenopathy (p < 0.001). Female sex and Moderna vaccine were predisposing factors (p = 0.005 and p = 0.003, respectively). Five or more enlarged lymph nodes were noted in 2% (8/433). Enlarged lymph nodes ≥ 10 mm in the short axis were noted in 1% (4/433). The median signal intensity relative to the muscle on T2WI was 4.0. Enlarged lymph nodes demonstrated a higher signal intensity on T2WI (p = 0.002). The median ADC of enlarged lymph nodes post vaccination was 1.1 × 10-3 mm2/sec with the range 0.6 - 2.0 × 10-3 mm2/sec in 90 participants, and thus ADC remained normal. Conclusion Axillary lymphadenopathy after the second dose of Pfizer-BioNtech or Moderna COVID-19 vaccination was frequent within two weeks after vaccination, was typically less than 10mm in size, and had normal ADC.