Case report

A 48-year-old man has been suffering from cervical lymphadenopathy, increased sweating, and weakness since September 2020, when he recovered from bilateral pneumonia (not associated with COVID-19 infection). After two non-diagnostic biopsies of the cervical and axillary lymph nodes (September and October 2020), the patient was eventually diagnosed with marginal zone lymphoma (MZL) based on a surgical biopsy of the right axillary lymph node on February 2021.

The [18F]FDG PET/CT scan was performed on 12th March 2021 for MZL staging before the treatment initiation. The reference mediastinum blood pool SUVmax was 1.8, and the liver background SUVmax was 2.6.

Coronal and axial CT scans demonstrated pathological lymph nodes located on both sides of the neck, both axillae, anterior mediastinum, and both inguinal regions. The [18F]FDG PET/CT (Fig. 1) presented mild uptake in a nodal mass of the neck, right axillary fossa, anterior mediastinum, and both inguinal regions with the SUVmax up to 2.0.

In the enlarged lymph nodes of the left axilla, the diffuse [18F]FDG uptake was also slightly increased (SUVmax 2.3), but one axillary lymph node with the size of 13 × 9 mm had higher, focal uptake of the tracer with SUVmax reaching 4.1. Furthermore, an area of mild increased [18F]FDG uptake was found in the left triceps brachii muscle (SUVmax 2.2).

Correlating it with the patient’s medical history, it was established that the second dose of the Pfizer BioNTech COVID-19 vaccination had been performed two days before the scan. We hypothesize that the significantly higher focal uptake of [18F]FDG tracer in the region of the left axilla, compared with the remaining enlarged lymph nodes was associated with an overlapping inflammatory reaction to the recent vaccine injection and MZL.

Due to the low glucose metabolism in the baseline examination (typical for MZL), PET/CT scan will not be useful for assessing the response to treatment in this case.

Conclusions

This case shows a new PET/CT image pitfall interpretation associated with the current COVID-19 pandemic vaccination program. To avoid incorrect image interpretation and inadvertent upstaging of the disease we recommend paying special attention to the recent vaccination in the patient’s medical history and taking it into account while interpreting the images. We recommend also rescheduling PET/CT scan, i.e. delaying it by several days after vaccination as long as the clinical status and management protocol allows it.

Conflict of interest

There is no conflict of interest to declare.