Widespread Reactive Lymphatic and Splenic FDG Avidity After mRNA COVID Vaccination

A 75-year-old woman with history of metastatic lung adenocarcinoma in remission develops new widespread FDG-avid lymphadenopathy in the neck, chest, abdomen, and pelvis on surveillance PET/CT, as well as intense FDG uptake in the spleen, without evidence of local recurrence. Short-term follow-up PET demonstrates near-complete resolution of FDG-avid lymphatic and splenic FDG avidity without interval change in management. Further history reveals that the patient received her fifth dose of COVID mRNA vaccine 6 days before the abnormal PET. Although unilateral axillary adenopathy after COVID vaccination is well-recognized, this widespread symmetric lymphatic and splenic FDG avidity is a significantly rarer phenomenon.