key: cord-0710337-noykshif
authors: Smith, Mathew V.; Yang, Ming
title: Reactive Axillary Lymphadenopathy to COVID-19 Vaccination on (18)F-FDG PET/CT
date: 2021-09-03
journal: J Nucl Med Technol
DOI: 10.2967/jnmt.121.262008
sha: 16e17b4498254ba2e2484709fc35bbe4ce6442ea
doc_id: 710337
cord_uid: noykshif

In this report, we present (18)F-FDG PET/CT findings of reactive left axillary and supraclavicular hypermetabolic lymphadenopathy, as well as ipsilateral deltoid muscle injection site radiotracer uptake, related to recent coronavirus disease 2019 (COVID-19) vaccination in a patient with osteosarcoma. With the growing number of patients receiving COVID-19 vaccine, recognition of benign characteristic (18)F-FDG PET/CT image findings will ensure staging and restaging accuracy and avoid unnecessary biopsy.

React ive lymphadenopathy is a recognized side effect related to vaccination. With messenger RNA-based coronavirus disease 2019 (COVID-19) vaccines, efficacy depends on the activation of dendritic cells after administration. These activated antigen-presenting cells must then migrate to the draining lymph nodes and present the translated protein to the node-based B and T cells in order to create robust humoral and cell-mediated adaptive immunity (1) . As more oncologic patients start to receive COVID-19 vaccines, it is important to recognize the benign 18 F-FDG PET/CT imaging features immediately after vaccination to ensure staging accuracy and prevent unnecessary biopsy.

A 40-y-old woman with a history of metastatic left proximal tibia osteosarcoma underwent surveillant 18 F-FDG PET/ CT. There was no radiotracer uptake suggestive of tumor recurrence. However, multiple morphologically benignappearing hypermetabolic lymph nodes were visualized at the left axillary and supraclavicular regions, as well as focal uptake in the left deltoid muscle (Fig. 1) . On further interview, the patient revealed receiving her second dose of the BNT162b2 vaccine (Pfizer/BioNTech) against SARS-CoV-2 the day before the 18 F-FDG PET/CT scan. She also stated that she had experienced pain at the left-upper-arm injection site, intense body aches, headaches, and a slight fever. Combined with inoculation history and characteristic imaging features, as well as exclusion of tracer injection at ipsilateral arm, a diagnosis of reactive lymphadenopathy secondary to COVID-19 vaccination was achieved.

Reactive lymphadenopathy is one of the well-documented reactions after intramuscular injection of COVID-19 vaccine and is likely secondary to a robust vaccine-elicited immune response (2, 3) . The efficacy of messenger RNA COVID-19 vaccine depends on encoding dendritic cell migration to draining lymph nodes in order to kickstart the complex humoral and cell-mediated response and, ultimately, to establish immunity (2) . There are rich draining lymph nodes at the axillary region that may show an immediate response after vaccination (4, 5) . 18 F-FDG is a glucose analog and is nonspecifically trapped in metabolically active tumor cells and benign conditions such as infection and inflammation, potentially leading to false-positive interpretations on oncologic 18 F-FDG PET/CT scans (6) . Among the most common etiologies of hypermetabolic axillary lymph nodes on 18 F-FDG PET/CT scans are malignancies, reactive changes, and lymphatic drainage of radiotracer extravasation. 

Visualization of early events in mRNA vaccine delivery in non-human primates via PET-CT and near-infrared imaging

Safety and efficacy of the BNT162b2 MRNA Covid-19 vaccine

Efficacy and safety of the mRNA-1273 SARS-CoV-2 vaccine

Lymph node activation by PET/CT following vaccination with licensed vaccines for human papillomaviruses

Duration of 18 F-FDG avidity in lymph nodes after pandemic H1N1v and seasonal influenza vaccination

Infection imaging using whole-body FDG-PET

No potential conflict of interest relevant to this article was reported.