Frequency and Characteristics of Nodal and Deltoid FDG and 11C-Choline Uptake on PET Imaging Performed After COVID-19 Vaccination.

Abstract

Background: COVID-19 vaccination may trigger reactive lymphadenopathy, confounding imaging interpretation. There has been limited systematic analysis of PET findings after COVID-19 vaccination. Objective: To evaluate the frequency and characteristics of abnormal FDG and 11C-choline uptake on PET imaging performed after COVID-19 vaccination. Methods: This retrospective study included 67 patients (mean age 75.6±9.2 years; 43 men, 24 women) who underwent PET examination (PET/CT in 66, PET/MRI in 1; FDG in 54, 11C-choline in 13) between December 14th 2020 and March 10th 2021 following COVID-19 vaccination (Pfizer-BioNTech vaccine in 52, Moderna vaccine in 15) and who had undergone pre-vaccination PET without visible axillary node uptake. PET was performed a median of 13 and 10 days after vaccination in patients who had received one (n = 44) and two (n = 23) doses, respectively. Two nuclear medicine physicians independently reviewed images, blinded to injection laterality and days since vaccination. Lymph node or deltoid SUVmax greater than blood pool SUVmax was considered positive. Interreader agreement was assessed, and the more experienced physician s measurements were used for subsequent analysis. Results: Positive axillary lymph node uptake was observed in 10.4% (7/67) of patients [7.4% (4/54) of FDG examinations, 23.1% (3/13) of 11C-choline examinations]; four and three patients with positive axillary lymph nodes had received Pfizer and Moderna vaccines, respectively. Injection laterality was documented in five of seven patients with positive axillary lymph nodes and was ipsilateral to the positive node in all five patients. PET was performed within 24 days of vaccination in all patients with a positive node. One patient exhibited extra-axillary lymph node uptake (ipsilateral supraclavicular uptake on FDG PET). Ipsilateral deltoid uptake was present in 14.5% (8/55) of patients with documented injection laterality, including in 42.9% (3/7) of patients with positive axillary lymph nodes. Interreader agreement for SUV measurements ranged from intraclass correlation coefficient of 0.600 to 0.988. Conclusion: Increased axillary lymph node or ipsilateral deltoid uptake is occasionally observed on FDG or 11C-choline PET performed after Pfizer-BioNTech or Moderna COVID-19 vaccination. Clinical impact: Interpreting physicians should recognize characteristics of abnormal uptake on PET after COVID-19 vaccination to guide optimal follow-up management and reduce unnecessary biopsies.