FIGURE 2.

FDG PET/CT performed 3 months later and 4 days after the second dose of mRNA COVID-19 vaccination shows expected postvaccination changes of FDG uptake at the injection site in the right deltoid (arrowhead) and ipsilateral FDG-avid axillary and subpectoral lymph nodes (curved arrows). However, newly FDG-avid mediastinal lymph nodes (thin arrow) were also noted, as well as new FDG-avid ground-glass and interlobular septal thickening in the right upper lobe, superior segment right lower lobe, and left upper lobes (thick arrows). The differential diagnosis for the lung parenchymal findings included recurrent disease manifesting as lymphangitis carcinomatosis; however, given the atypical pattern of spread and the well-demarcated field of involvement, a diagnosis of radiation recall triggered by COVID-19 vaccination was proposed. The patient remained asymptomatic, and further investigation with bronchoscopy was therefore deferred.