The Day after Mass COVID-19 Vaccination: Higher Hypermetabolic Lymphadenopathy Detection on PET/CT and Impact on Oncologic Patients Management

SIMPLE SUMMARY: The mass COVID-19 vaccination led to unexpected PET findings. Notably, axillary and interpectoral lymphadenopathies ipsilateral to the vaccine inoculation were observed, but could be wrongly interpreted, complicating cancer patients’ management. Our study aimed to assess the hypermetabolic lymphadenopathy detection rate on PET/CT and investigated factors that might help in lymphadenopathy interpretation. A significantly higher vaccine-related lymphadenopathy detection rate resulted in the vaccinated population, as well as in younger and vaccinated patients within 20 days before PET. SUVmax significantly changed during different time intervals, with the lowest values beyond 20 days. To minimize misdiagnosis, a detailed vaccination anamnesis must be recorded and should take into account the appropriate PET schedule, preferable to be performed 20 days after vaccine. Since this health emergency situation will probably continue in the near future, with the need for a strong vaccination campaign for the whole population, it is essential to keep in mind these considerations in order to better manage and take care of oncologic patients. ABSTRACT: The widespread COVID-19 vaccination led to unexpected PET findings. Notably, axillary and interpectoral lymphadenopathies ipsilateral to the vaccine inoculation were observed. We aimed to assess the hypermetabolic lymphadenopathy (HLN) detection rate on PET/CT. Secondly, we investigated factors that might help in HLN differential diagnosis. A retrospective analysis on 1196 consecutive patients referred for a PET/CT was performed. All patients were asked about the date, type and site of vaccine injections. HLNs were recorded and categorized according to risk classes and SUVmax grades. A statistical analysis was performed to assess the correlation between HLN detection and different clinical/vaccine data. HLN detection rate was 15% and 27% in the No Vac- and vac-groups (p < 0.001), respectively. In the Vac-group, age (p < 0.001) and time interval from vaccine-to-PET (p = 0.010) were inversely correlated with HLN detection. Furthermore, SUVmax significantly changed during time intervals, with lower values beyond 20 days (p < 0.001). In the era of mass COVID-19 vaccination, a higher axillary and interpectoral lymphadenopathies detection ipsilateral to vaccine injection was observed. These PET findings can be wrongly interpreted, complicating cancer patients’ management. To minimize these pitfalls, a detailed vaccination anamnesis must be recorded and should take into account the appropriate PET schedule.