Detection of Unilateral Axillary Nodal Uptake Both at 68Ga-DOTATOC and 18F-FDG PET/CT After 1 Week From COVID-19 Vaccine.

ABSTRACT: Recently, vaccination against COVID-19 has gained wide diffusion, especially among vulnerable individuals, such as cancer patients. At the same time, patients have been undergoing PET/CT examinations after vaccination in an increasing number, and cases of false-positive axillary nodal uptake have been described, mostly at 18F-FDG PET. Here, we describe the case of both 68Ga-DOTATOC and 18F-FDG axillary nodal uptake in a young woman affected by a metastatic retroperitoneal paraganglioma.

We describe the case of a 29-year-old woman with stage IV retroperitoneal paraganglioma and disseminated bone metastases, who underwent both 68Ga-DOTATOC and 18F-FDG PET/CT during her follow-up. After the injection of 101 MBq of 68Ga-DOTATOC, the PET/CT examination revealed a stable disease in the already known numerous bone and pulmonary metastases; furthermore, a mild uptake was demonstrated in some small left axillary nodes (white and black arrows; A, MIP; B, axial PET image; C, CT image; D, fused PET/CT image). The day after, she underwent 18F-FDG PET/CT confirming bone and lung lesions and a mild uptake (SUVmax, 3.80) in the left axillary region, corresponding to the small nodes with fatty hilus previously observed (white and black arrows; E, axial PET image; F, CT image; G, fused PET/CT image; H, MIP). A fade uptake was also detected within the subcutaneous soft tissues superficial to the left deltoid muscle. The patient presented a history of receiving the Pfizer-BioNTech COVID-19 vaccine in the left deltoid muscle 6 and 7 days before the 68Ga-DOTATOC and the 18F-FDG PET/CT, respectively. Tracer injection was via the right (contralateral) antecubital fossa in both examinations, hence not a potential cause. Clinical correlation and its morphological aspect supported the nodal uptake to be reactive, ascribed to the recent vaccination. Similar findings were described after COVID-19 vaccinations (both Pfizer-BioNTech and AZ) on 18F-FDG PET/CT[1-7] and, recently, also on 18F-choline PET/CT examination.[8] To the best of our knowledge, this is the first case of a COVID-19 vaccine–related nodal uptake on 68Ga-DOTATOC PET/CT, as very recently another case involving 68Ga-DOTATATE PET/CT had been reported.[9] This case highlights another potential pitfall associated with the current COVID-19 pandemic vaccination program, which may result in incorrect image interpretation and inadvertent disease upstaging.