Lessons Learned from Post-COVID-19 Vaccination PET/CT Studies.

Area of Science:

• Radiology and Nuclear Medicine
• Immunology
• Public Health

Background:

• COVID-19 vaccination has introduced new diagnostic challenges in medical imaging.
• Post-vaccination lymphadenopathy with increased PET/CT uptake can be misinterpreted as malignancy, leading to unnecessary investigations.

Purpose of the Study:

• To analyze PET/CT findings following Pfizer-BioNTech COVID-19 vaccination.
• To characterize the imaging appearance of lymphadenopathy and arm uptake using various PET tracers.
• To prevent misinterpretation of PET/CT studies in vaccinated individuals.

Main Methods:

• Retrospective analysis of 1,018 PET/CT studies performed between January 1, 2021, and February 15, 2021.
• Correlation of axillary-neck lymphadenopathy and arm uptake with vaccination dates and sites.
• Visual and semiquantitative assessment of PET tracer uptake.

Main Results:

• Unilateral axillary lymphadenopathy with increased uptake was observed in 66% of vaccinated patients.
• The "double sign" (DS), simultaneous increased uptake in the arm and ipsilateral axillary lymph nodes, was present in 20% of patients.
• DS demonstrated 100% specificity and 100% positive predictive value for post-vaccination lymphadenopathy, with no cases observed beyond 21 days after the second dose.

Conclusions:

• COVID-19 vaccination frequently induces nonspecific axillary lymphadenopathy with increased PET tracer activity.
• The "double sign" (DS) is a highly specific indicator of post-vaccination changes, aiding in the avoidance of unnecessary diagnostic procedures.
• Familiarity with these imaging findings is crucial for accurate interpretation of PET/CT scans in vaccinated populations.