Timeline for Resolution of Incidentally Detected Sonographic Lymphadenopathy Reactive to mRNA COVID-19 Vaccination

Purpose: COVID-19 vaccination with the Pfizer-BioNTech mRNA is associated with post-vaccination lymphadenopathy, but the timeline for its resolution remains unclear. This study describes the resolution pattern of incidentally detected post-vaccination lymphadenopathy in women referred for routine breast ultrasound examinations.

Methods: Between Jan-March 2021 women referred for breast ultrasound, if demonstrating axillary lymphadenopathy of ≥3 mm cortical thickness, were questioned whether they underwent a recent COVID-19 vaccination. If vaccinated in the ipsilateral arm within 6 weeks, serial follow-up axillary ultrasound was performed every 3 weeks until lymphadenopathy resolved. Data was collected and analyzed retrospectively.

Results: Forty-one women were included in the study. Time from the second COVID-19 vaccine injection ranged from 1 day to 6 weeks (mean 2.2; median 2). Cortical thickness at presentation ranged between 3-9 mm (mean 4.4). At 3-5 weeks of follow-up (n=38) lymphadenopathy resolved in 17/38 (45%), and persisted in 21/38 (55%) with cortical thickness between 3-7 mm. At 6-8 weeks (n=13), lymphadenopathy resolved in 7/13 (54%) and persisted in 6/13 (46%) with cortical thickness ranging between 3-5 mm. By 9 weeks (n=5) lymphadenopathy persisted in 3/5 (60%) women, consequently biopsied at 12 weeks, with benign pathology and documented resolution by 21 weeks. Overall, lymphadenopathy persisted ≥6 weeks in 32% and ≥9 weeks in 12%.

Conclusion: Post COVID-19 vaccination related sonographically detected axillary lymphadenopathy, persisted in one of three women for ≥6 weeks, and in 12% for ≥9 weeks. This timeline should be considered in guiding management.